1. Genetic explanation
Family, twin and adoption Biological
studies
explanations
of Depression

2. 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

3. 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

4. Genetics & Depression
Qu. How do you ‘prove’ a
genetic argument for any
behaviour?
Twin studies:
Allen, 1976 Bertelsen 1977
MZ 40% 59%
Qu. Problems?
DZ 11% 30%

5. Genetics & Depression
Family concordance rates
Gershon 1990 Wender 1986
Gen Pop 15% 15%
Family 40-50% 70% if adopted
Qu. Problems?

6. Genetic explanation DEPRESSION
RESEARCHER
Family studies
“In 1990, I reviewed many
family studies …
… in each study, depression
was assessed in the first
degree relatives of patients
with depression …
Gershon
“I showed that depression
rates in these first degree
relatives was about two to
three times the rate in the
general population …
“My work was supported by Sullivan et al
(2000), who showed similar findings in a
review of several family studies…

7. Genetic explanation McGuffin 1996
Twin studies
“In twin studies, we look at
CONCORDANCE RATES for
depression in MZ and DZ
twins …
“If depression is
MZ twins have identical genes!
caused by a gene,
If depression is caused by
genes, then if they have the we would expect
gene they should BOTH have that MZ twins
depression! either BOTH have
depression, or
“So we would NEITHER have
expect to find a depression … DZ twins share 50% of their
genes!
HIGHER
CONCORDANCE So one twin could have the
gene for depression, while the
for depression in
other doesn’t!
MZ twins than in
DZ twins …

8. Genetic explanation McGuffin
Twin studies
“Here are the twin study
research findings …
“In 1976, Allen
reviewed MZ/DZ
studies and found a
MZ: either both have the gene
for depression, or neither
mean concordance
does – so should be concordant rate of 40% for MZ
twins, and just 11%
for DZ twins …
“In 1977, Bertelson
et al found a “In 1996, my team DZ: might both have the gene,
concordance of 59% and I found 46% both not have the gene, or one
for MZ twins, and concordance for could have the gene and one
30% for DZ twins … might not have it! This means
depression in MZ we expect a lower concordance
twins, and just 20% for depression in DZ twins,
in DZ twins … than we do in MZ twins

9. Genetic explanation McGuffin
Twin studies
“I’ll summarise the findings
for you …
TWIN STUDIES …
Allen (1976) MZ 40%
DZ 11%
CONCORDANT FOR DEPRESSION?
Bertelson (1977) MZ 59%
DZ 30%
McGuffin (1996) MZ 46%
DZ 20%
“Do these data
support the idea that “Thinking about what CONCORDANT FOR DEPRESSION?
depression is caused you understand
by genes? … about genes and
MZ/DZ twins, can
you criticise these
findings? …

10. Genetic explanation Wender
Adoption studies “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
What causes depression depression, because they didn’t
separate genes from environment …
“Adoption studies
are an improvement,
because they
eliminate the
influence of the
family environment …

11. Genetic explanation Wender
“I published two
Adoption studies 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! “Both sets of
findings suggest
When we looked at adopted children who that genetics play
later developed depression, we found that a big part in
their biological parents were EIGHT depression …
TIMES more likely than their adoptive
parents, to have suffered from depression
And we’re happy
I’m feeling So am I …
… so why is our
prickly but I don’t
adopted lad
today… know why!
depressed???
We’re both
okay!
What a
nice day!
Parents with Parent with
Biological parent adopted child biological child