Nightmares: Familial aggregation and association with psychiatric disorders in a nationwide twin cohort

We quantified the genetic influences affecting the liability to nightmares, and the association between nightmares and psychiatric disorders in a comm unity-based sample. In 1990, 1,298 monozygotic (MZ) and 2,419 dizygotic (DZ ) twin pairs aged 33-60 years responded to a questionnaire study in the Fin nish Twin Cohort. Structural equation modeling was used to estimate genetic and environmental components of variance in the liability to nightmares. R ecords on hospitalization and long-term antipsychotic medication were used to estimate the period prevalence of serious psychiatric disorders, Nightma res were reported more frequently in females both in childhood and as adult s, The correlation between occurrence in childhood and as adults was 0.69 i n males and 0.71 in females. Polychoric correlations of occurrence within t he twin pairs were 0.45 in MZ and 0.21 in DZ pairs in childhood, and as adu lts 0.39 and 0.18, respectively. The best fitting genetic model was that sp ecifying additive genetic and unshared environmental effects. The estimated proportion of genetic effects in childhood was in males 44% (95% confidenc e interval [CI] 35-52%) and in females 45% (95% CI 38-52%) of the phenotypi c variance. As adults the values were in males 36% (95% CI 27-44%) and in f emales 38% (95% CI 31-45%), Nightmare frequency and psychiatric disorders w ere linearly associated. Among those with the most frequent nightmares odds ratios (95% CI) were 3.67 (2.48-5.42) for childhood and 5.87 (4.08-8.45) f or adults compared with those never having nightmares. Nightmares are quite a stable trait from childhood to middle age. There are persistent genetic effects on the disposition to nightmares both in childhood and adulthood. N ightmares are significantly associated with psychiatric disorders. Am, J, M ed, Genet, (Neuropsychiatr, Genet.) 88:329-336, 1999. (C) 1999 Wiley-Liss, Inc.