Biological explanations of Depression Genetic explanation Family, twin and adoption studies
Biological explanations
of Depression
Genetic explanationFamily, twin and adoption studies
Mood Disorders – Genetic
• Depression tends to run in families
• The closer the relationship with a sufferer, the more likely a person will have a mood disorder
• Genetic evidence is strongest for most severe forms of the disorder
• Concordance rates also indicate a substantial environmental contribution
Mood Disorders – Genetic
• Zubenko et al (2001)– Family history – 50% of FD relatives, 25% of
SD relatives also had mood disorder– Relatives had increased risk of suicide & liver
disease
Genetics & Depression
Qu. How do you ‘prove’ a genetic
argument for any behaviour?Twin
studies:
MZ
DZ
Allen, 1976
40%
11%
Bertelsen 1977
59%
30%
Qu. Problems?
Genetics & DepressionFamily concordance
rates
Gen Pop
Gershon 1990
15%
40-50%
Wender 1986
15%
70% if adopted
Qu. Problems?
Family
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
depression …
“My work was supported by Sullivan et al (2000), who showed
similar findings in a review of several family studies…
Genetic explanationTwin studies
McGuffin 1996
“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 depression were SEVEN TIMES more likely than adoptive relatives to have had depression themselves!When we looked at adopted children who later developed depression, 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 child
Parent with biological child