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Taller 2 Genética. Departamento de Biología Celular e Histología
1° Unidad Académica, FMED, UBA.
1
TALLER 2 DE GENÉTICA
Guía de actividades
PARTE 1. Las enfermedades monogénicas en la genética clínica
Andrés tiene 3 años y padece Hemofilia A (entidad monogénica que produce alteración en el
proceso de coagulación por ausencia de Factor 8), esto le provoca grandes sangrados a mínimos
roces. Andrés es el segundo hijo de Juan Cruz (34 años) y Lucía (28 años). El hermano de Andrés
se llama Axel (8 años) y es sano. Lucía le relata que en su familia hay varios afectados de
hemofilia: Gabriel (hermano de Lucia), Lionel (sobrino de Lucia; hijo de su hermana Marcela) y
Gustavo (tío materno de Lucia ya fallecido). Lucía no presenta hemofilia, pero le comenta que
solamente en los partos de sus hijos tuvo sangrados importantes que requirieron intervención
médica.
1.1 Dibuje el árbol genealógico de esta familia1.
1.2 Justifique a qué tipo de herencia preferentemente podría corresponder este caso. Marque
en el árbol los portadores obligados, si es que los hubiere.
1.3 La pareja le pregunta: ¿cómo puede explicarse que los individuos afectados de la familia de
Lucía son únicamente varones? ¿fue por azar? ¿Las grandes hemorragias de Lucía en los partos
pueden estar relacionadas con la hemofilia A de su familia? ¿Qué les responde? Justifique
1.4 Si tuvieran deseos de planificar un próximo embarazo ¿Qué riesgo de recurrencia de
afectación le informaría a esta pareja? Justifique.
PARTE 2. La investigación básica de los determinantes genéticos de enfermedades
monogénicas
El siguiente caso se encuentran basado en el trabajo de investigación “Mutaciones en el gen de
profilina 1 causan esclerosis lateral amiotrófica familiar” de Wu C.H. y colaboradores (Nature,
2012).
Introducción:
Le esclerosis lateral amiotrófica (ELA) es un trastorno neurodegenerativo caracterizado por la
muerte de neuronas motoras superiores (con somas en núcleos cerebrales) e inferiores (con
somas en la médula espinal). Los síntomas de la enfermedad, que suelen aparecer en la vida
adulta, involucran debilidad muscular y pérdida rápida y progresiva del control de los
movimientos voluntarios. La muerte de los individuos afectados suele estar asociada a fallas
respiratorias y ocurre, en promedio, tres años después de la aparición de los síntomas.
Las características patológicas típicas de la enfermedad incluyen palidez del tracto corticoespinal
debido a la muerte de neuronas motoras, la presencia de inclusiones citoplasmáticas positivas
1 Puede consultar las convenciones de la nomenclatura estándar para la construcción de árboles genealógicos o pedigrees en el siguiente trabajo, que figura como ANEXO al final de esta Guía de Actividades: Bennett, R. L., French, K. S., Resta, R. G., & Doyle, D. L. (2008). Standardized human pedigree nomenclature: Update and assessment of the recommendations of the National Society of Genetic Counselors. Journal of Genetic Counseling, 17(5), 424–433.
Taller 2 Genética. Departamento de Biología Celular e Histología
1° Unidad Académica, FMED, UBA.
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para ubiquitina dentro de las neuronas motoras sobrevivientes, y deposición de agregados
patológicos de la proteína TDP-43.
Aproximadamente el 10% de los casos son familiares (ELA familiar) y se transmiten con un patrón
de herencia monogénico. El resto de los casos son esporádicos (ELA esporádica). Al momento
del inicio de la investigación se habían reportado que SOD1, FUS y TDP-43 eran genes causantes
de ELA familiar en distintas familias. Sin embargo, hay otras familias con miembros afectados
con ELA que no poseen mutaciones en esos genes. La motivación para identificar nuevos genes
causantes de ELA familiar radica en que el descubrimiento de cada nuevo gen implicado en la
etiología de esta enfermedad permite comprender mejor la patogénesis de la degeneración de
las neuronas motoras y facilita el desarrollo de modelos experimentales. Además, aumenta las
probabilidades de generar terapias específicas exitosas.
2.1 De acuerdo con la información del párrafo anterior, puede afirmarse que la ELA familiar es
una entidad con heterogeneidad de locus. Defina este concepto.
Objetivo y metodología:
Con el objetivo de identificar nuevos genes causantes de ELA familiar, los autores del trabajo de
investigación seleccionaron dos familias con miembros afectados por ELA, sin mutaciones en los
genes SOD1, FUS y TDP-43. La familia 1 posee origen caucásico y la familia 2 origen judío sefaradí.
Los pedigrees de ambas familias se muestran en la Figura 1. Para preservar la identidad de las
familias se omitió indicar el sexo de los individuos allí representados.
Para identificar los genes causantes de ELA familiar, se escogieron dos miembros afectados de
cada una de esas familias para realizar una secuenciación de exoma completo (SEC) a partir de
una muestra de sangre de los mismos. La SEC es una de las variantes de la secuenciación de alto
rendimiento y se basa en la secuenciación en paralelo de millones de moléculas de ADN que
provienen del ∼1,5% del genoma que codifica para proteínas (exoma). La potencia de esta
técnica, en el contexto del presente trabajo de investigación, se basa en el hecho de que la gran
FAMILIA 1
FAMILIA 2
Figura 1. Pedigrees de las familias analizadas en el trabajo de investigación
Taller 2 Genética. Departamento de Biología Celular e Histología
1° Unidad Académica, FMED, UBA.
3
mayoría de variantes patogénicas conocidas (∼85%) surgen por mutaciones que se encuentran
dentro de la región codificadora de proteínas del genoma2.
2.2 Teniendo en cuenta los pedigrees de las familias 1 y 2. ¿Cuál es el patrón de herencia con el
que se transmite la ELA familiar? Justifique
2.3 Los investigadores utilizan la técnica de SEC para identificar los genes causantes de ELA
familiar. ¿Podría haberse utilizado, en forma alternativa, secuenciación de Sanger? ¿PCR?
¿Southern blot? Justifique su respuesta en cada caso.
Resultados:
La identificación de los fragmentos de ADN secuenciados implica determinar los loci del genoma
de los que ellos derivan. La identificación se llevó a cabo mediante la comparación de su
secuencia nucleotídica con una base de datos del genoma humano.
Para determinar cuáles de las secuencias identificadas podrían corresponder a la variante
patogénica causante de ELA familiar, las mismas fueron filtradas progresivamente utilizando los
criterios señalados en la Tabla 1. Notar que en cada paso de filtrado sólo se analizan las
secuencias que han superado el filtrado de los pasos anteriores.
Tabla 1: Descripción de los pasos de filtrado (=selección progresiva) de las secuencias
identificadas por medio de SEC.
2.4 Explique por qué el criterio utilizado en cada paso de filtrado (1 a 6) contribuye a identificar
la variante patogénica causante de la ELA familiar.
2 “Ten years of next-generation sequencing technology”. Van Dijk EL, et al.Trends Genet. 2014; 30: 418-426. 3 Bases de datos consultadas (disponibles online): Single Nucleotide Polymorphism database (dbSPN 132), 1000 Genomes Project (May 2011 release) y NHLBI Exome Sequencing Project (ESP) Exome Variant Server. 4 El paso de filtrado número 6 está basado en información adicional al de la secuenciación del exoma completo de los dos individuos por familia. Esa información adicional fue obtenida de otros miembros afectados de las familias en los que se analizaron los transcriptos-candidatos que surgen del paso 5 mediante secuenciación de Sanger.
Familia 1 Familia 2
Número total de secuencias identificadas en las dos muestras de cada familia 282.782 382.751
1- Número de secuencias pertenecientes a regiones codificantes
29.777 42.661
2- Número de secuencias comunes a ambas muestras de cada familia 9.045 10.669
3- Número de secuencias no reportadas como ‘no patogénicos’ en bases de datos relevantes consultadas3
18 178
4- Número de secuencias provenientes de genes en heterocigosis y que representen variantes no sinónimas
10 135
5- Número de secuencias confirmados por secuenciación de Sanger 2 6
6- Número de secuencias presentes en todos los miembros afectados de la familia4
2 3
Taller 2 Genética. Departamento de Biología Celular e Histología
1° Unidad Académica, FMED, UBA.
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El número resultante de candidatos identificados como potenciales mutaciones causales de ELA
familiar fueron dos para la familia 1 y tres para la familia 2 (ver Tabla 2).
Tabla 2: Genes candidatos obtenidos para cada familia
Gen Mutación Nombre completo del gen
Familia 1 PFN1 C71G Profilina-1
XPOT V139A Exportina de tARN
Familia 2 FMO2 T390I Dimetilalanina monooxigenasa 2
KIF1C I118L Proteína similar a la kinesina KIF1C
PFN1 M114T Profilina-1
Un hecho a destacar es que ambas familias contienen diferentes mutaciones (C71G y M114T)
para un mismo gen: PFN1 (gen de profilina 1), localizado en el cromosoma 17p13.2. La proteína
PFN1 posee 140 aminoácidos y es un regulador central del crecimiento de los filamentos de
actina mediante su unión a la actina monomérica.
En base al resultado obtenido mediante la secuenciación del exoma y los pasos de filtrado
posteriores los investigadores sugieren que mutaciones en el gen PFN1 pueden causar ELA
familiar.
2.5 Clasifique a las mutaciones encontradas en el gen PFN1 según los criterios señalados a
continuación. Justifique en cada caso su elección:
a- Mutaciones somáticas/ de línea germinal
b- Mutaciones puntuales/ de extensión variable
c- Mutaciones de sustitución/ inserción/ deleción
d- Mutaciones sinónimas /de cambio de sentido/ sin sentido
e- Mutaciones de pérdida/ ganancia de función
2.6 Los datos encontrados muestran que en los casos de ELA familiar en los que está implicado
PFN1 hay heterogeneidad alélica. Defina este concepto. Compárelo y diferéncielo del concepto
heterogeneidad de locus, definido en la pregunta 2.1.
Taller 2 Genética. Departamento de Biología Celular e Histología
1° Unidad Académica, FMED, UBA.
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La Figura 2 muestra el genotipo de aquellos miembros de las familias cuyo ADN estuvo
disponible para el análisis de secuenciación (de Sanger) del gen PFN1.
Los cuatro miembros afectados que fueron analizados de la familia 1 poseían la variante C71G
del gen PFN1. Un único portador obligado de la variante C71G (III:13), no desarrolló la
enfermedad; sin embargo, la muerte de este individuo ocurrió antes de los 50 años, que es la
edad promedio de aparición de síntomas en esta familia. Todos los miembros no afectados de
la familia 1 que fueron analizados poseen el genotipo wild type.
En familia 2, los ocho individuos afectados que fueron analizados poseían la variante M114T. Un
noveno individuo, cuyo ADN no estaba disponible, fue confirmado como poseedor de la variante
M114T (III:2) sobre la base de los genotipos de su compañero reproductivo y sus hijos (no
mostrados en el pedigree). De los 7 miembros no afectados que fueron analizados, 5 no poseen
la variante M11T. Uno de los individuos que no está afectado y es portador de la mutación tiene
45 años (III:15) y un segundo portador obligado (II:4) fue asintomático hasta su muerte, que
ocurrió a los 78 años.
En referencia al párrafo anterior:
2.7 El genotipo del individuo III:2 es inferido a partir del análisis del genotipo de otros individuos
¿Cuál debe ser el genotipo del compañero reproductivo y de los hijos para inferir que ese
individuo es heterocigota para la variante M114T?
2.8 ¿Qué conclusiones puede sacar respecto de la penetrancia de las mutaciones C71G y M114T
del gen de PFN1 sobre el fenotipo de ELA familiar?
FAMILIA 1
FAMILIA 2
Figura 2. Pedigrees de las familias analizadas en el trabajo de investigación indicando el genotipo para
el locus de PFN (sólo hay información de algunos miembros). w: wild type; m: mutante. Los asteriscos
indican los individuos seleccionados para SEC. +: Genotipo inferido (no secuenciado directamente).
Taller 2 Genética. Departamento de Biología Celular e Histología
1° Unidad Académica, FMED, UBA.
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Validaciones posteriores al análisis de SEC:
Para validar a las mutaciones C71G y M114T del gen PFN1 como causantes de ELA familiar son
necesarios ensayos de investigación básica. En ese contexto, dados los impedimentos éticos y
prácticos de la experimentación en humanos, el uso de modelos animales es una herramienta
particularmente informativa.
2.9 Considere la generación de un ratón genéticamente modificado con la técnica de
CRISPR/Cas:
a. Describa brevemente en qué consiste la técnica en su variante de generación de un ratón KO
(knock-out) para un gen y en su variante de generación de un KI (knock-in)
b. ¿Cuál de los dos abordajes de la técnica de CRISPR/Cas le parece más conveniente para
generar un modelo adecuado para estudiar el efecto de las mutaciones de PFN1 halladas
mediante SEC? Justifique.
Para seguir practicando:
Se sugiere realizar los ejercicios 2 y 3 de la “Guía complementaria de
actividades de práctica y autoevaluación”
PROFESSIONAL ISSUES
Standardized Human Pedigree Nomenclature: Updateand Assessment of the Recommendations of the NationalSociety of Genetic Counselors
Robin L. Bennett & Kathryn Steinhaus French &
Robert G. Resta & Debra Lochner Doyle
Received: 12 April 2008 /Accepted: 29 May 2008 /Published online: 16 September 2008# National Society of Genetic Counselors, Inc. 2008
Abstract In 1995, the Pedigree Standardization Task Force(PSTF) of the National Society of Genetic Counselors(NSGC) proposed a system of pedigree nomenclature.Recently, the PSTF (now called the Pedigree Standardiza-tion Work Group or PSWG) sought evidence that thepublished symbols met the needs of health professionals,were incorporated into health professional training andwere utilized in publications. We searched PubMed andreference lists of select publications, reviewed the Instruc-tions for Authors of several journals, searched the websitesof professional societies, sought comment from the mem-bership of the NSGC, and looked at recommendations andtraining practices of various health professional organiza-tions. Many journals still do not cite specific standards forpedigrees, but those found cited the PSTF nomenclature.We did not find significant objections or alternatives to the1995 nomenclature. Based on our review, we propose onlya few minor stylistic changes to the pedigree symbols. The
pedigree nomenclature of the NSGC is the only consistentlyacknowledged standard for drawing a family health history.We recommend regular and continued review of thesepedigree standards to determine if additional symbols areneeded to accommodate changes in clinical practice toensure that the symbols continue to meet the needs ofhealth professionals and researchers as well as adhere toevolving ethical and privacy standards. All health profes-sionals, trainees, and researchers should be made aware ofthe utility of using a common pedigree nomenclature inclinical practice and publication. This will become partic-ularly important as electronic medical records become morewidely utilized.
Keywords Electronic medical record . Family history .
Genetic counseling . National Society ofGenetic Counselors .
Pedigree symbols . Pedigree standardization
Introduction
A medical pedigree is a graphic presentation of a family’shealth history and genetic relationships and it has been apivotal tool in the practice of medical genetics for nearly acentury (Bennett 1999; Resta 1993). With the mapping ofthe human genome and the increasing role of genetics indaily medical practice, recording and interpreting a pedi-gree should be a standard competency of all healthprofessionals (Bennett 1999; Center for Disease Control2008; HHS 2008; NCHPEG 1995).
In the early 1990s, the National Society of GeneticCounselors Pedigree Standardization Task Force (NSGCPSTF) documented that even genetics professionals wereusing an inconsistent array of symbols and nomenclature torecord pedigrees (Bennett et al. 1993; Steinhaus et al. 1995).
J Genet Counsel (2008) 17:424–433DOI 10.1007/s10897-008-9169-9
R. L. Bennett (*)Division of Medical Genetics, Department of Medicine,University of Washington Medical Center,Box 357720, Seattle, WA 98195-7720, USAe-mail: [email protected]
K. S. FrenchDivision of Genetics and Metabolism, University of California,Irvine,Orange, CA, USA
R. G. RestaHereditary Cancer Clinic, Swedish Cancer Institute,Seattle, WA, USA
D. L. DoyleGenetic Services Section,Washington State Department of Health,Seattle, WA, USA
The PSTF worked with professional genetic societies,prominent medical genetics professionals, genetics educa-tors, and patient advocacy groups to develop standardizedpedigree nomenclature (Bennett et al. 1995). In this review,we assess the utilization and acceptance of the 1995 pedigreenomenclature by health professionals, educators, and inpublications. A systematic review of clinical practice was notperformed, although a literature review was conducted. Wepropose some minor stylistic changes to the nomenclatureand provide suggestions for future development.
Pedigree Nomenclature in Publications
The NSGC Pedigree Standardization Work Group (PSWG)employed several strategies to determine if there werechallenges to the standardized pedigree nomenclaturepublished in 1995. To look for published references to thenomenclature we searched PubMed using the key wordspedigree nomenclature, pedigree standards, pedigree stan-dardization, family history standards, family history stan-dardization, and family history nomenclature over theperiod of 1994 to August 2007. Using SCOPUS Preview(2007), we searched for journal articles in English that citedthe nomenclature. The Instructions for Authors of Englishlanguage journals with a focus on clinical genetics that havea history of publishing pedigrees were reviewed to see ifPSTF nomenclature was recommended. The websites ofseveral professional societies of journal editors weresearched for recommendations for publishing pedigrees.
The PSTF nomenclature is referred to in a variety ofclassical human genetics texts (referenced in Table 1). TheAMA Manual of Style (2007) and several human andmedical genetics journals cite the PSTF recommendationsin their Instructions for Authors (American Journal of HumanGenetics (http://images.cell.com), American Journal of Med-ical Genetics (http://www3.interscience.wiley.com), Geneticsin Medicine (http://edmgr.ovid.com), and Journal of GeneticCounseling (www.springer.com)). Other genetics journalswith a significant focus on clinical genetics did not have anyrecommendations in their Instructions to Authors regardingthe publication of pedigrees or specific standards for drawingpedigrees (such as Clinical Genetics (http://blackwellpublishing.com), European Journal of Human Genetics(http://www.nature.com/ejhg), European Journal of MedicalGenetics (http://www.elsevier.com), New England Journal ofMedicine (www.nejm.org), Nature Genetics (www.nature.com/ng), and Lancet (www.thelancet.com)). We are notaware of any clinical genetic journals that expound adifferent pedigree nomenclature to use in publications thanthat proposed by the PSTF. The websites for the Council ofBiology Editors (http://writing.colostate.edu), the EuropeanAssociation of Science Editors (http:www.ease.org.uk), the
International Committee of Medical Journal Editors (http://www.icmje.org), and theWorld Association ofMedical Editors(http://www.wame.org) do not include guidance for publica-tion of pedigrees.
Scientific and medical journals as well as professionalsocieties of journal editors should adopt standardizedpedigree nomenclature. As we documented previously(Steinhaus et al. 1995), wide variation in pedigree nomen-clature (even within the same journal) can potentially leadto misinterpretation of data and errant scientific conclusionsbased on the publication of the pedigree.
Publication of Pedigrees and Confidentiality
When pedigrees are published, journals should assure thatstandardized nomenclature is followed. Care should betaken to preserve patient and family confidentiality,particularly since the widespread availability of profession-al journals and scientific reporting makes it more likely thata pedigree will be recognized by a family member or byindividuals familiar with the family. Researchers shouldconsider obtaining consent from research participants toallow publication of a pedigree when enrolling subjects in astudy, and to show participants a sample of a genericpedigree that is similar to one that might appear in apublication (Bennett 2000; Byers and Ashkenas 1998). A
Table 1 Examples of Journals, Text and Reference Books WhichInclude the National Society of Genetic Counselors Standard PedigreeNomenclature
General reference
AMA Manual of Style. A Guide for Authors and Editors, 10thEdition (2007)
JournalsAmerican Journal of Medical GeneticsAmerican Journal of Human GeneticsGenetics in MedicineJournal of Genetic CounselingText booksA Guide to Genetic Counseling (Schuette and Bennett 1998)ASCO Curriculum: Cancer Genetics and Cancer Predisposition, 2ndedition (2004)
Emery’s Elements of Medical Genetics, 13th edition (Turnpenny andEllard 2007)
Emery and Rimoin’s Principles and Practice of Medical Genetics, 5thEdition (Kingston 2007)
Neurogenetics: Scientific and Clinical Advances (Bennett 2006a)Oxford Desk Reference: Clinical Genetics (Firth et al. 2005)Principles of Molecular Medicine, 2nd Edition (Bennett 2006b)The Genetic Basis of Common Disease, 2nd Edition (LeRoy andWalker 2002)
Thompson & Thompson, Genetics in Medicine, 7th Edition(Nussbaum et al. 2007)
Update of Standardized Pedigree Nomenclature 425
pedigree should not contain information about which asubject had no prior knowledge. In other words, a personwho had presymptomatic or susceptibility genetic testingthrough research should not find out about increased ordecreased disease risk status from a publication. Likewise,health professionals have a duty to warn a patient aboutpotential genetic risks to the patient’s relatives (Offitt et al.2004); such conversations should occur before the publica-tion of a pedigree (Bennett 2000; Botkin et al. 1998). Topreserve confidentiality, the minimum amount of informa-tion needed to convey the scientific finding should beincluded on the published pedigree. Authors should askthemselves how they would feel if their own pedigrees werebeing published and if the information would make them ortheir families uncomfortable (Bennett 2000).
The practice of masking or altering pedigrees should beaddressed by the various societies and councils of journaleditors along with the use of standard pedigree nomenclature.We discourage masking or altering pedigrees (Bennett 2000).Masking, which is usually evident to the reader, refers to anobvious change in the pedigree such as using diamonds tohide gender on a pedigree. Alteration involves changinginformation such as birth order or gender. A survey of 177investigators who published pedigrees in peer reviewedjournals indicated that 19% had altered the pedigree and45% had not disclosed their alterations to the journal editor(Botkin et al. 1998). Although the minimal amount ofinformation needed to provide scientific documentationshould be used in a published pedigree, it is also essentialto maintain the integrity of the pedigree with proper birthorder, ages, and affected status as this information may bevital to pedigree interpretation. Alteration may hinder therecognition of important genetic paradigms such as antici-pation, parent of origin effects, sex-linked or sex-limitedexpression, or in utero lethality. In addition, genetic andenvironmental factors that alter disease expression, orconfounding effects of having common ancestors (as maybe noted in the offspring of consanguineous unions or inpopulations with a high coefficient of inbreeding), may bemissed if pedigrees are altered or masked (Bennett 2000).
Usage of the PSTF Nomenclature in Health ProfessionalTraining, Certification and Credentialing
We contacted the Transnational Alliance of GeneticCounselors (http://igce.med.sc.edu) and the directors ofgenetic counseling training programs that are accredited bythe American Board of Genetic Counseling (http://www.abgc.net) (ABGC) to determine if the NSGC PSTFnomenclature was used in training of genetic counselorsworldwide. We also communicated with the executivedirectors of the certifying or credentialing organizations
for genetic counselors (ABGC), medical geneticists (Amer-ican Board of Medical Genetics (http://www.abmg.org)),and advanced practice genetic nurses (the Genetic NurseCredentialing Committee (http://www.geneticnurse.org)) todocument whether the PSTF nomenclature was used inexamination questions or in the credentialing process.
All genetic counseling training programs in NorthAmerica accredited by the ABGC use the nomenclature. Aquery of the Transnational Alliance for Genetic Counselingnotes use of the PSTF nomenclature in genetics professionaltraining programs in Australia, China, South Africa, theUnited Kingdom, France, Israel, Spain, and Japan. Asevidenced by educational resources on their websites.
Many professional societies have introduced the nomen-clature to their membership as part of genetics/genomicsfamily history initiatives, including The National Coalitionfor Health Professional Education in Genetics (NCHPEG1995) (which includes representatives from over 100diverse health organizations), the American Medical Asso-ciation (http://www.ama-assn.org), the American Academyof Family Physicians (http://www.aafp.org), the AmericanAcademy of Physicians Assistants (http://pa.nchpeg.org),the American Society of Clinical Oncologists (ASCO 2004),the United Kingdom’s Clinical Genetics Society (http://www.clingensoc.org), and the China Genetic CounselingNetwork (www.gcnet.org.cn). Jenkins and Calzone (2007)document a coalition of nursing societies that advocatefor use of the PSTF nomenclature as a component oftaking and interpreting a family history as a core nursingcompetency.
Changes Proposed to the Pedigree Nomenclature
We found no comprehensive alternative pedigree nomencla-tures or recurring criticisms of the PSTF’s recommendations.In June of 2002 and again in June of 2007, we solicited open-ended comments regarding use of the pedigree nomenclaturefrom members of the NSGC through its general listserv.Comments collected from the NSGC membership regardinguse of the pedigree nomenclature were mostly related tostylistic preferences as compared to changes in the actualsymbols, and there were no new comments that had notalready been addressed in 1995, in the development of theoriginal nomenclature. Figures 1, 2, 3 and 4 reflect minorchanges from the original 1995 nomenclature. The follow-ing changes and the respective rationale are noted:
1. A diamond for the “individual symbol” can be used toreflect persons with gender not specified and can beused for persons with congenital disorders of sexdevelopments (DSD) and also with transgenderedindividuals (Fig. 1.1). The concept of gender identity
426 Bennett et al.
has evolved over the last decade. Current practice is toavoid early assignment of gender for people withdisorders of sex development (defined by Vilain andcolleagues as ‘congenital conditions in which develop-ment of chromosomal, gonadal, or anatomic sex isatypical’) (Vilain et al. 2007). In addition, someindividuals identify themselves somewhere along the
spectrum between the opposites of male and female(Adultsociety.com 2007). The Pedigree StandardizationWork Group continues to recommend that the male orfemale symbol be used to define the phenotypic gender,with the karyotype noted below the symbol, when known.This might be important, for example, in identifying thecancer risks faced by a BRCA mutation carrier who has
Instructions:— Key should contain all information relevant to interpretation of pedigree (e.g., define fill/shading) — For clinical (non-published) pedigrees include:
a) name of proband/consultandb) family names/initials of relatives for identification, as appropriate c) name and title of person recording pedigreed) historian (person relaying family history information)e) date of intake/updatef) reason for taking pedigree (e.g., abnormal ultrasound, familial cancer, developmental delay, etc.)g) ancestry of both sides of family
— Recommended order of information placed below symbol (or to lower right)a) age; can note year of birth (e.g., b.1978) and/or death (e.g., d. 2007)b) evaluation (see Figure 4)c) pedigree number (e.g., I-1, I-2, I-3)
— Limit identifying information to maintain confidentiality and privacy
Male Female Gender not specified
Comments
1. Individual Assign gender by phenotype (see text for disorders of sex development, etc.). Do not write age in symbol.
2. Affected individual Key/legend used to define shading or other fill (e.g., hatches, dots, etc.). Use only when individual is clinically affected.
With >2 conditions, the individual’s symbol can be partitionedaccordingly, each segment shaded with a different fill and defined in legend.
3. Multiple individuals,number known
Number of siblings written inside symbol. (Affected individuals should not be grouped).
4. Multiple individuals, number unknown or unstated
"n" used in place of "?".
5. Deceased individual Indicate cause of death if known. Do not use a cross ( )to indicate death to avoid confusion with evaluation positive (+).
6. Consultand Individual(s) seeking genetic counseling/testing.
7. Proband An affected family member coming to medical attention independent of other family members.
8.Stillbirth (SB) Include gestational age and karyotype, if known.
9. Pregnancy (P) Gestational age and karyotype below symbol. Light shading can be used for affected; define in key/legend.
Pregnancies not carried to term Affected Unaffected
10. Spontaneous abortion (SAB) If gestational age/gender known, write below symbol. Key/legend used to define shading.
11. Termination of pregnancy (TOP) Other abbreviations (e.g., TAB, VTOP) not used for sake of consistency.
12. Ectopic pregnancy (ECT) Write ECT below symbol.
b. 1925 30y 4 mo
5 5 5
n n n
d. 35 d. 4 mo d. 60's
P P
SB28 wk
SB30 wk
SB34 wk
P P P
< 10 wks
18 wks47,XY,+18
ECT
LMP: 7/1/200747,XY,+21
20 wk46,XX
17 wks femalecystic hygroma
Fig. 1 Common PedigreeSymbols, Definitions, andAbbreviations.
Update of Standardized Pedigree Nomenclature 427
undergone female-to-male transgender surgery. A dia-mond can be used when it is not clinically relevant toassign gender (Fig. 1.1)
2. We no longer use a shorter “individual’s line” forpregnancies not carried to term (Figs. 2.1–2.2). Apregnancy not carried to term is distinguished fromother symbols by the unique use of a triangle, therebymaking the shorter individual’s line redundant graph-ically (Figs. 1.10–1.12).
3. We recommend including on the pedigree the indica-tion for referral (reason for taking the pedigree) such as“abnormal ultrasound,” “familial cancer,” etc (seeFig. 1 Instructions). This helps to clarify the orientationof the information collected on the pedigree, because
all pedigrees document information from directedhealth queries recording the consultand’s personalmedical and family history (Bennett 1999).
4. The Instructions (Fig. 1) were changed for therecorder to include less identifying information onthe pedigree to be compliant with the Health Informa-tion Privacy, Access and Accountability Act (HIPAA)standards in the United States (http://www.hipaa.org).Initials or first names (in lieu of full names) may beenough to identify persons where medical records aredocumented and for orientation of discussions with thepatient. Use of birth year or age, year of death or age atdeath, rather than birth date or date of death, would bemore compliant with HIPAA guidelines since a full
1. Defi nitions Comments
If possible, male partner should be to left of female partner on rela-tionship line.
Siblings should be listed from left to right in birth order (oldest to youngest).
2. Relationship line (horizontal)
a. Relationships A break in a relationship line indicates the relationship no longer exists. Multiple previous partners do not need to be shown if they do not affect genetic assessment.
b. Consanguinity If degree of relationship not obvious from pedigree, it should be stated (e.g., third cousins) above relationship line.
3. Line of descent (vertical or diagonal)
a. Genetic Biologic parents shown.
- Multiple gestation
The horizontal line indicat-ing monozygosity is placed between the individual’s line and not between each symbol. An asterisk (*) can be used if zygosity proven.
- Family history not available/known for individual
- No children by choice or reason unknown
Indicate reason, if known.
- Infertility Indicate reason, if known.
b. Adoption Brackets used for all adoptions. Adoptive and biological parents denoted by dashed and solid lines of descent, respectively.
1. relationship line
2. line of descent
4. individual’s line
3. sibship line
Monozygotic Dizygotic Unknown Trizygotic
?
? ?
or
vasectomy tubal
or
azoospermia endometriosis
in out by relative
Fig. 2 Pedigree LineDefinitions.
428 Bennett et al.
birth date or date of death is considered private andprotected information.
Recording Pedigrees for Persons and Pregnanciesin Relation to Assisted Reproductive Technologies
The symbolization for depicting pregnancies achievedthrough assisted reproductive technologies (Fig. 3) hasbeen widely adopted. A dashed line of descent, used toidentify a non-biological parental relationship (Fig. 2.3b), isparticularly useful for documenting parental gamete donor,and gestational carrier relationships to a pregnancy. How-ever, the nomenclature does not show documentation offrozen embryos or transferred embryos. The convention of“E” for evaluation (Fig. 4) could be used to track genetic
testing of transferred embryos, but this has not been usedextensively by the community of professionals involvedwith assisted reproductive technologies. Further review isneeded to consider the complexities of pedigree documen-tation of the number of embryos conceived, frozen, andimplanted, along with their genetic testing history, partic-ularly given that embryos may be “adopted” from “donorparents,” and the high frequency of multiple gestationsassociated with assisted reproduction.
Tracking Genetic Evaluation and Testing on a Pedigree
NSGC members reported that the symbolization for GeneticEvaluation and Testing (Fig. 4) is not widely used,particularly the use of “E” for evaluation. Figure 4.3 hasbeen generally accepted as the symbol for a person who is
Instructions:— D represents egg or sperm donor — S represents surrogate (gestational carrier)— If the woman is both the ovum donor and a surrogate, in the interest of genetic assessment, she will only be
referred to as a donor (e.g., 4 and 5) ); the pregnancy symbol and its line of descent are positioned below the woman who is carrying the pregnancy
— Available family history should be noted on the gamete donor and/or gestational carrier
Possible Reproductive Scenarios Comments1. Sperm donor Couple in which woman is carrying preg-
nancy using donor sperm. No relationship line is shown between the woman carrying the pregnancy and the sperm donor.
2. Ovum donor Couple in which woman is carrying pregnancy using a donor egg and partner’s sperm. The line of descent from the birth mother is solid because there is a biologic relationship that may affect the fetus (e.g., teratogens).
3. Surrogate only Couple whose gametes are used to impregnate a woman (surrogate) who carries the pregnancy. The line of descent from the surrogate is solid because there is a biological relationship that may affect the fetus (e.g., teratogens).
4. Surrogate ovum donor
Couple in which male partner’s spermis used to inseminate a) an unrelated woman or b) a sister who is carrying the pregnancy for the couple.
5. Planned adoption
Couple contracts with a woman to carry a pregnancy using ovum of the woman carry-ing the pregnancy and donor sperm.
or
D D
PP
D
P
P
S
a) b)
D
P
D
P
or
DD
P
Fig. 3 Assisted ReproductiveTechnology Symbols andDefinitions.
Update of Standardized Pedigree Nomenclature 429
currently unaffected and tested positive for a condition andwho can develop the disease (e.g., a person testing positivefor a BRCA2 gene mutation who has no cancer at the timeof evaluation). Some practitioners use a dot in the middle ofthe symbol for a heterozygous carrier of an x-linkeddisorder and a symbol shaded in half for a heterozygouscarrier of an autosomal recessive disorder. We continue tosupport denoting carrier status based on phenotypicexpression of the disease and not based on pattern ofinheritance.
The Challenge of Incorporating the Pedigreein the Electronic Medical Record (EMR)
The NSGC PSTF recommendations provide a clear andconcise pedigree nomenclature that is widely but notuniformly used. No alternative comprehensive symboliza-
tion recommendations have been proposed nor did weidentify literature or professional provider organizationsrefuting the NSGC PSTF recommendations. With this inmind, we would encourage manufacturers developing EMRsystems to consider the inclusion of the standardizedpedigree nomenclature within their products.
The family health information contained within EMRsgives rise to new challenges because medical records maybe accessed to varying degrees by a variety of differentpeople (e.g., the patient, health care providers, hospitaladministration, etc.). Therefore, protocols should be devel-oped to identify who can access pedigree information, andwhat information to include on the pedigree. During thespring of 2007, the Washington State Department of HealthGenetic Services Section and the University of WashingtonMedical Center’s Division of Medical Genetics convened aseries of meetings designed to explore these issues (Bennettet al. 2007). The meeting participants included medical
Instructions:— E is used for evaluation to represent clinical and/or test information on the pedigree
a. E is to be defined in key/legendb. If more than one evaluation, use subscript (El, E2, E3) and define in keyc. Test results should be put in parentheses or defined in key/legend
— A symbol is shaded only when an individual is clinically symptomatic — For linkage studies, haplotype information is written below the individual. The haplotype of interest should be
on left and appropriately highlighted— Repetitive sequences, trinucleotides and expansion numbers are written with affected allele first and placed in
parentheses— If mutation known, identify in parentheses
Definition Symbol Scenario
1. Documented evaluation (*) Use only if examined/evaluated by you or your research/clinical team or if the outside evaluation has been reviewed and verified.
Woman with negative echocardiogram.
2. Carrier—not likely to manifest disease regardless of inheritance pattern
Male carrier of Tay-Sachs disease by patient report (* not used because results not verified).
3. Asymptomatic/presymptomatic carrier—clinically unaffected at this time but could later exhibit symptoms
Woman age 25 with negative mammogram and positive BRCA1 DNA test.
4. Uninformative study (u) Man age 25 with normal physical exam and uninformative DNA test for Huntington disease (E2).
5. Affected individual with positive evaluation (E+)
Individual with cystic fibrosis and positive mutation study; only one mutation has currently been identified.
10 week male fetus with a trisomy 18 karyotype.
*
E− (echo)
E+
*25 yEu
*25 y
E1− (mammogram)E2+(5385insC BRCA1)
E1− (physical exam)E2u (36n/18n)
E+(∆F508/u)*
EuE+(∆F508)
E+(CVS)47, XY,+18
P*
10wk
*
Fig. 4 Pedigree Symbols ofGenetic Evaluation/TestingInformation.
430 Bennett et al.
geneticists and genetic counselors, consumers, researchers,information technology staff, primary care providers,HIPAA compliance officers, and health administrators.Samples of anonymous pedigrees taken from the regionalgenetics clinics in Washington State were examined todetermine the content of information on the pedigree andwhy it was obtained. While few regional genetic clinicswere utilizing electronic medical records, this exercise setthe stage for discussing the potential risks, benefits andlimitations of incorporating pedigrees within EMRs.
The conclusions from these meetings were that theelements of a pedigree are consistently recorded for theoverall purposes of: 1. orientation, 2. risk assessment, 3.ease of reading by multiple users, 4. validation 5.accountability 6. education/health promotion and interven-tion, and 7. communication (Bennett 1999; Bennett et al.2007). To expand on the above categories, pedigreeelements related to issues of orientation refer to the user’sunderstanding of who is the consultand or proband,understanding the genetic and biologic relationships withinthe documented family, knowing when the pedigree wasobtained or the information updated, who provided andrecorded the information, and why the pedigree was beingconstructed. Pedigree elements relevant for risk assess-ment include knowing who on the pedigree is affected orunaffected, relationship lines depicting the biologic rela-tionships and degrees of relatedness (including consan-guinity), ancestry, ages of relatives including age atdisease onset, and other pertinent healthcare information.Elements such as using the standardized symbols andincluding legends or keys are included for ease of readingby multiple users. Knowing whether the informationprovided was actually validated, for example, by review-ing medical records or death certificates, is important forrisk assessment and health intervention. Information isalso recorded on a pedigree to meet documentation andaccountability demands for medical-legal standards. Fi-nally, information on a pedigree is used for education ofthe patient and to develop plans for health interventionsand health promotion.
An over-riding principle is the use of a pedigree forcommunication between the health professional and thepatient, communication with other health professionals, andpotentially sharing the pedigree with relatives (Bennett1999; Bennett et al. 2007). There is a delicate balancebetween recording enough information to make a pedigreeuseful and including so much information that the pedigreecan no longer be quickly and concisely interpreted. Thepedigree’s utility lies in its ability to simply and graphicallydepict complex information so that disease patterns, risks,and biological relationships are immediately and obviouslyapparent. If the pedigree becomes cluttered with irrelevantinformation, its usefulness is diminished.
In a health care environment with EMRs, one canimagine that a pedigree will be revised throughout thelifetime of a patient when he or she faces new age-relatedhealth risks. For example, the familial disorders that shouldbe tracked for a newborn are different than for anadolescent, a pregnant woman, or a male over age 60(Bennett 1999). As different providers obtain or update thepedigree, they may direct their inquiries about the familyhealth history in targeted ways. For example, an obstetri-cian may ask questions to determine risk factors for thefetus, while the same patient in later years may see acardiologist whose questions of her family health historywould clearly be focused on cardiovascular disease risks.The fill patterns in a pedigree that are identified in the keyare likely to change as different disorders arise in theperson’s family and as the number of relatives increase insize and age. Ideally, to reduce such pedigree “clutter,” anEMR would allow the viewer with access to the pedigreeinformation to eliminate or filter excess information notcurrently relevant to the patient’s care (e.g., the cardiologistcould omit elements of the pedigree obtained during theobstetrical visit that are not relevant to the patient’s currentconcern of cardiovascular disease).
Privacy and Confidentiality
It’s also important to recognize that pedigrees documentsensitive information that should be collected and maintainedwith the utmost protection for privacy and confidentiality.Individual pedigree symbols have low information content,but when they are formatted into a pedigree, there is a newrepresentation of the family and the individual’s relation to it.The previously independent data become a collective workmaking “invisible knowledge” visible to the patient, family,and potentially the scientific community (Bennett 2000;Nukaga and Cambrosio 1997). The PSWG suggests that innon-published pedigrees, initials or first names (in lieu of fullnames) may be enough to identify persons where medicalrecords are documented and for orientation of discussionswith the patient. Use of birth year or age, year of death orage at death, rather than birth date or date of death, would becompliant with HIPAA guidelines where exact dates areviewed as private and protected information.
Summary
The NSGC PSTF recommendations provide a clear andconcise pedigree nomenclature that is widely but notuniformly used. No alternative comprehensive symbolizationrecommendations have been proposed. Although we did notperform an exhaustive search of the literature regarding the
Update of Standardized Pedigree Nomenclature 431
use of the PSTF nomenclature, or look at the website ofevery professional society whose members might use apedigree in clinical practice; we found no evidence of a trendto refute the NSGC PSTF recommendations.
The pedigree nomenclature published by the NationalSociety of Genetic Counselors in 1995 is becoming aninternational standard. Upon review, we propose a fewstylistic changes only. The century-old adage of FrancisGalton (1889) that “there are many methods of drawingpedigrees and describing kinship, but for my own purposesI still prefer those that I designed myself,” remains an issuetoday. Emphasis on using standardized pedigree nomencla-ture should continue in genetic education, documentation ofmedical records, genetic research, and in publication. Useof this nomenclature has the potential to reduce medicalerror and ease communication among health professionals,patients and their families regarding genetic diagnosis andtesting. It also has the potential to save money bydocumenting prior testing so that additional diagnostic orsusceptibility genetic testing can be approached in a cost-efficient manner (e.g., testing for a known mutation insteadof full sequencing, or offering an expanded panel of genetictesting that might not have existed at the time a relative wastested, etc.). The use of this nomenclature should bereviewed periodically to assure that it is sensitive tochanging legal requirements, responsive to changing med-ical and testing technologies, successfully incorporated intoelectronic medical records, and always respectful of patientconfidentiality. A simple litmus test in documentation of apedigree should be: would you feel comfortable handingthis pedigree to your patient, or would you be willing tohave this pedigree published if it was your family?
Acknowledgements The pedigree symbols and abbreviations arerevised with permission from Cell Press and were originally publishedin Bennett, R. L. et al. (1995). Recommendations for standardizedpedigree nomenclature. American Journal of Human Genetics, 56,745–752. Meetings and conference calls of the PSWG were supportedby grants from the National Society of Genetic Counselors, theUniversity of Washington Division of Medical Genetics. TheMamafest gift fund of University of Washington Division of MedicalGenetics provided support for graphic artist Christine Symonds. TheBoard of Directors of the National Society of Genetic Counselorsreviewed and approved the revisions to the pedigree nomenclature onOctober 16, 2007. The pedigree symbols in the figures were formattedusing Adobe InDesign CS2. None of the authors received financialcompensation for their work. The meetings regarding Core Elementsof the Pedigree in the Electronic Medical Record were supported inpart by Project # H61MC00219 from the Maternal and Child HealthBureau (Title V, Social Security Act), Health Resources and ServicesAdministration, Department of Health and Human Services.
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