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Colombo Twin & Singleton Study (COTASS)
measuring depression and its environmental correlates directly!
(such
as poverty)
With the support of the Wellcome Trust,
we have ascertained all twins in Colombo, Sri Lanka
(population 2.23M), and comprising 19,302 individual twins.
This is the only truly population based twin sample in a
developing country. We have completed data collection from a
random sample of 1954 complete twin pairs and a parallel
study of 2019 non-twin individuals using the same sampling
frame. The main phenotypes assessed have been common mental
disorders (anxiety and depression), substance use (nicotine
and alcohol), and post traumatic stress disorder using the
Composite International Diagnostic Interview (CIDI); and
physical symptoms, fatigue and disability. We measured
environmental exposures, including socio-economic status,
poverty related variables, life events, early childhood
experiences, and experiences related to the tsunami and
civil war. We attained a greater than 90% participation rate
for twins and non-twins. Early findings for depression
indicate that prevalence is lower than in many Western
countries, symptom patterns are similar, and there was a
significant interaction between sex and risk factors of low
education and low access to material resources. These risk
factors were strongly associated with depression in men but
not in women. At the same time, a sex interaction applied to
behavioural genetic models, showed a high heritability in
women, but low (or no) heritability in men. Analyses of
nicotine use, and related disorders, has shown patterns of
heritability similar to Western populations, as well as a
changing relationship between heritability and age. Use of
the substances was strongly determined by shared environment
in early adult life, but became increasingly more genetic in
older twins, a pattern also observed in the developed
countries. |
