HEMOGLOBIN, 1 5 ( 4 ) , 309-311 ( 1 9 9 1 )

SHORT COMMUNZCATZON

HIGH PREVALENCE OF a-THALASSEMIA I N A BLACK POPULATION OF BRAZIL

A h i g h f requency o f a- tha lassemia ( a - t h a l ) i n a c l i n i c a l l y normal B lack p o p u l a t i o n o f B r a z i l has been observed through t h e d e t e c t i o n and q u a n t i f i c a t i o n o f Hb B a r t ' s i n c o r d b lood specimens. Hb B a r t ' s was p resen t i n 38 o f t h e 320 newborns analyzed (11.9%). The l e v e l s showed a bimodal d i s t r i b u t i o n : 10.3% o f t h e i n f a n t s f e l l i n t h e 1-3.5% range and 1.6% i n t h e 5-10% range ( 1 ) . I n o r d e r t o c o n f i r m t h e h i g h f requency o f a d e l e t i o n a l t ype o f a - t h a l , we s t u d i e d 47 u n r e l a t e d B lack i n d i v i d u a l s ( b l o o d donors) b y DNA anal - y s i s ; 40 males and seven females f rom t h e r e g i o n o f Campinas, S t a t e o f Sao Paolo, i n Southeast B r a z i l .

H igh m o l e c u l a r we igh t DNA was i s o l a t e d f r o m p e r i p h e r a l b l o o d leukocy tes b y pheno l - ch lo ro fo rm e x t r a c t i o n u s i n g s tandard proce- dures ( 2 ) . Ten wg of DNA f rom each sample was d i g e s t e d w i t h Bam H I and Bgl I 1 (BRL) acco rd ing t o t h e m a n u f a c t u r e r ' s suggest ions, sub- j e c t e d t o e l e c t r o p h o r e s i s i n 0.8% agarose and t r a n s f e r r e d t o n i t r o - c e l l u l o s e o r n y l o n f i l t e r s ( 3 ) . The probe was a 1.5 kb genomic fragment of al-pSVO1 v e c t o r c o n t a i n i n g t h e a - g l o b i n gene ( 4 ) ; i t was l a b e l e d by n i c k t r a n s l a t i o n t o a s p e c i f i c a c t i v i t y o f 5 .0 x l o 7 cpm/ug. F o l l o w i n g h y b r i d i z a t i o n f o r 18 hours a t 42°C i n a s o l u t i o n c o n t a i n i n g 50% formamide, 1% sodium dodecyl s u l f a t e , 5 x SSC (0 .75 M sodium c h l o r i d e , 0.075 M sodium c i t r a t e ) , 0.02 M T r i s - HC1, pH 7 . 5 , 1% Denhard t ' s s o l u t i o n , 5% d e x t r a n - s u l f a t e , and 100 mg/ml salmon sperm DNA, t h e f i l t e r s were washed, d r i e d , and autoradiographed ( 2 ) .

The r e s u l t s demonstrated t h a t 10 i n d i v i d u a l s (21.3%) were heterozygous f o r a - t h a l - 2 ( -a /aa) . T h i s rep resen ts a f requency o f 0.125 f o r t h e tha lassemic hap lo type (-a/). A l l t e n DNA samples showed t h e -a3 -7 / hap lo type ( r i g h t w a r d d e l e t i o n ) . I n a d d i t i o n , we d e t e c t e d one a - t h a l - 2 homozygote ( - 2 - 7 / - 2 - 7 ) , and t h r e e i n d i - v i d u a l s heterozygous f o r an CX gene t r i p 1 i c a t i o n (aaaant1-3.7/aa) (Tab le I ) . Two s u b j e c t s heterozygous f o r a - t h a l - 2 were a l s o Hb S heterozygotes.

Our da ta c o n f i r m t h e h i g h prevalence o f a - t h a l - 2 i n t h e Black p o p u l a t i o n o f B r a z i l . T h i s p o p u l a t i o n seems t o be d i f f e r e n t f rom

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310 SONATI ET AL.

TABLE I Sizes ( i n kb) o f Fragments Obta ined From t h e DNA o f 47 B r a z i l i a n Blacks Using Barn H I and Bgl I 1 Endonucleases and an Gene Probe

Genotype Number ( % ) Barn H I Bgl I1

aalaa 33 (70.2) 14.0 12.6; 7.4 -a/aa 10 (21.3) 14.0; 10.5 16.0; 12.6; 7.4

-a / -a 1 ( 2.1) 10.5 16.0 aaa/aa 3 ( 6.4) 17.7; 14.0 12.6; 7.4; 3.7

American, Jamaican, and A f r i c a n p o p u l a t i o n s , where t h e l a r g e s t i n v e s t i g a t i o n s concern ing a - t h a l - 2 have been performed. There i s more admix tu re w i t h Europeans, as i n d i c a t e d b y a l a r g e p ropor - t i o n o f p a t i e n t s c l a s s i f i e d as " l i g h t m u l l a t o e s " ( 5 ) . However, t h e -a/ hap lo type f requency i s i n agreement w i t h t h e da ta r e p o r t e d f o r o t h e r B lack p o p u l a t i o n s i n Jamaica, t h e U n i t e d S ta tes , and A f r i c a (6,7,8). I n c o n t r a s t , t h e f requency o f t h e ...anti-3.7/ hap lo type was unexpectedly h igh , and a l a r g e r number o f B lack i n d i - v i d u a l s i n t h i s p o p u l a t i o n should be s t u d i e d i n o r d e r t o c o n f i r m t h e data. Our r e s u l t s a l s o i n d i c a t e t h a t q u a n t i t a t i o n o f Hb B a r t ' s i n c o r d b l o o d samples i s an u n r e l i a b l e method f o r t h e d e t e r m i n a t i o n o f t h e f requency o f t h e a - t h a l - 2 d e f i c i e n c y .

T h i s s t u d y was suppor ted b y FINEP, FAPESP, and CNPq - B r a s i l . The a u t h o r s a r e i ndeb ted t o E.M. Kimura, C.F. Ramos, and M.H. T a v e l l a f o r e x c e l l e n t t e c h n i c a l ass i s tance , and t o D r . B.G. Fo rge t f o r p r o v i d i n g t h e a - g l o b i n gene probe.

Departamento de P a t o l o g i a C1 i n i c a M.F. Sonat i

Departamento de Genet ica Medica

Departamento deAC1 i n i ca,Medi ca Faculdade de C i e n c i a s Medicas Un ive rs idade Estadual de Campinas-UNICAMP 13081 - Carnpinas (SP) - B r a s i l

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Received : Junucltry 4 , 1991. AcccpZtQd : Muy 3, 1991.

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