High concordance of bipolar I disorder in a nationwide sample of twins.
OBJECTIVE
The few studies of bipolar I disorder in twins have consistently emphasized the genetic contribution to disease liability. The authors report what appears to be the first twin study of bipolar I disorder involving a population-based twin sample, in which the diagnoses were made by using structured, personal interviews.


METHODS
All Finnish same-sex twins (N=19,124) born from 1940 to 1957 were screened for a diagnosis of bipolar I disorder as recorded in the National Hospital Discharge Register between 1969 and 1991 or self-reported in surveys of the Finnish Twin Cohort in 1975, 1981, and 1990. Thirty-eight pairs were thereby identified and invited to participate in the study; the participation rate was 68%. Lifetime diagnoses were made by using the Structured Clinical Interview for DSM-IV. The authors calculated probandwise and pairwise concordances and correlations in liability and applied biometrical model fitting.


RESULTS
The probandwise concordance rates were 0.43 (95% CI=0.10 to 0.82) for monozygotic twins and 0.06 (95% CI=0.00 to 0.27) for dizygotic twins. The correlations in liability were 0.85 and 0.41, respectively. The model with no familial transmission was rejected. The best-fitting model was the one in which genetic and specific environmental factors explained the variance in liability, with a heritability estimate of 0.93 (95% CI=0.69 to 1.00).


CONCLUSIONS
The high heritability of bipolar disorder was demonstrated in a nationwide population-based twin sample assessed with structured personal interviews.
Department of Mental Health and Alcohol Research, National Public Health Institute, 00300 Helsinki 30, Finland. tuula.kieseppa@ktl.fi.
Tuula
T
Kieseppä
Timo
T
Partonen
Jari
J
Haukka
Jaakko
J
Kaprio
Jouko
J
Lönnqvist
D000328:Adult; D001714:Bipolar Disorder / Q000175:diagnosis / Q000453:epidemiology / Q000235:genetics*; D015331:Cohort Studies; D004200:Diseases in Twins / Q000175:diagnosis / Q000453:epidemiology / Q000235:genetics*; D005260:Female; D005387:Finland / Q000453:epidemiology; D020022:Genetic Predisposition to Disease / Q000235:genetics*; D005820:Genetic Testing; D006801:Humans; D008297:Male; D008875:Middle Aged; D008957:Models, Genetic; D015995:Prevalence; D011569:Psychiatric Status Rating Scales / Q000706:statistics & numerical data; D011594:Psychometrics; D012042:Registries; D012307:Risk Factors; D012737:Sex Factors; D012931:Social Environment; D014429:Twins, Dizygotic / Q000235:genetics; D014430:Twins, Monozygotic / Q000235:genetics