Biological explanations

of Depression

Genetic explanation

Neurochemical explanation

Hormones explanation

Neuroendocrine explanation

The Amine Hypothesis

e.g. female hormones

SAM/HPA and cortisol

family, twin and adoption studies

“Hi – I’m Elliot Gershon.I carried out an

important FAMILY STUDY into the

inheritance of depression

Genetic explanationThree types of study

“And my name is Peter McGuffin. I conducted TWIN STUDIES which

looked for evidence that depression is

inherited

Elliot S GershonUniversity of Chicago

Peter McGuffinKings College London

Paul H WenderHarvard Medical School

Aside from saying that there could be a genetic basis for MDD, there isn’t a lot you can say about the actual theory – no single gene has been identified. Therefore, AO1 marks for this are earned by describing the research findings that suggest a genetic link …

“I’m Paul Wender. My method of researching the inheritance of depression is to

carry out ADOPTION STUDIES

Genetic explanationThree types of study

Wender

“We have all provided evidence

that depression runs in families,

suggesting a genetic explanation

McGuffin

Gershon

Start each day with a smileand get it over with

Genetic explanationFamily studies

Gershon

DEPRESSIONRESEARCHER

“I showed that depression rates in these first degree relatives was about two to three times the rate in the

general population …

“In 1990, I reviewed many family studies …

… in each study, depression was assessed in the first

degree relatives of patients with MDD …

“My work was supported by Sullivan et al (2000), who showed similar findings in a review of several family studies…

Genetic explanationTwin studies

McGuffin

“In twin studies, we look at CONCORDANCE RATES for depression in MZ and

DZ twins …

MZ twins have identical genes!If depression is caused by genes, then if they have the gene they should BOTH have depression!

DZ twins share 50% of their genes!

So one twin could have the gene for depression, while the other doesn’t!

“If depression is caused by a gene, we would expect that MZ twins

either BOTH have depression, or NEITHER have depression …

“So we would expect to find a

HIGHER CONCORDANCE for depression in MZ twins than in

DZ twins …

Genetic explanationTwin studies

McGuffin

“Here are the twin study research findings …

MZ: either both have the gene for depression, or neither does – so should be concordant

DZ: might both have the gene, both not have the gene, or one could have the gene and one might not have it! This means we expect a lower concordance for depression in DZ twins, than we do in MZ twins

“In 1976, Allen reviewed MZ/DZ

studies and found a mean concordance

rate of 40% for MZ twins, and just 11%

for DZ twins …

“In 1977, Bertelson et al found a

concordance of 59% for MZ twins, and

30% for DZ twins …

“In 1996, my team and I found 46% concordance for depression in MZ

twins, and just 20% in DZ twins …

Genetic explanationTwin studies

McGuffin

“I’ll summarise the findings for you …

CONCORDANT FOR DEPRESSION?

CONCORDANT FOR DEPRESSION?

TWIN STUDIES …Allen (1976) MZ 40% DZ 11%Bertelson (1977) MZ 59% DZ 30%McGuffin (1996) MZ 46% DZ 20%

“Do these data support the idea that depression is

caused by genes? …

“Thinking about what you understand about genes and

MZ/DZ twins, can you criticise these

findings? …

Genetic explanationAdoption studies

Wender

“I looked at adoption studies, because when a child is adopted, it is

taken away from its home and family environment …

“Family studies like Gershon’s, and twin studies like McGuffin’s, can’t say genes are the only reason for depression, because they didn’t

separate genes from environment …

“Adoption studies are an improvement,

because they eliminate the

influence of the family environment …

What causes depression

Genetic explanationAdoption studies

Wender

“Both sets of findings suggest

that genetics play a big part in depression …

“I published two sets of findings

in 1986 …We found that biological relatives of adopted sufferers of MDD were SEVEN TIMES more likely than adoptive relatives to have had MDD themselves!

When we looked at adopted children who later developed MDD, we found that their biological parents were EIGHT TIMES more likely than their adoptive parents, to have suffered from depression

I’m feeling prickly today…

So am I … but I don’t know why!

And we’re happy … so why is our

adopted lad depressed???

We’re both okay!

What a nice day!

Biological parentParents with

adopted childParent with

biological child