Dissecting the catatonia phenotype in psychotic and mood disorders on the basis of familial-genetic factors.

BACKGROUND: This study examines the familial aggregation (familiality) of different phenotypic definitions of catatonia in a sample of multiplex families with psychotic and mood disorders.

METHODS: Participants were probands with a lifetime diagnosis of a DSM-IV functional psychotic disorder, their parents and at least one first-degree relative with a psychotic disorder. The study sample included 441 families comprising 2703 subjects, of whom 1094 were affected and 1609 unaffected. Familiality (h2 ) was estimated by linear mixed models using family membership as a random effect, with h2 indicating the portion of phenotypic variance accounted for by family membership.

RESULTS: Familiality estimates highly varied for individual catatonia signs (h2 =0.17-0.65), principal component analysis-derived factors (h2 =0.29-0.49), number of catatonia signs present (h2 =0.03-0.43) and severity of the catatonia syndrome (h2 =0.25-0.59). Phenotypes maximizing familiality estimates included individual signs (mutism and rigidity, both h2 =0.65), presence of ≥5 catatonia signs (h2 =0.43), a classical catatonia factor (h2 =0.49), a DSM-IV catatonia syndrome at a severity level of moderate or higher (h2 =0.59) and the diagnostic construct of psychosis with prominent catatonia features (h2 =0.56). Familiality estimates of a DSM-IV catatonia syndrome did not significantly differ across the diagnostic categories of psychotic and mood disorders (h2 =0.40-0.47).

CONCLUSIONS: The way in which catatonia is defined has a strong impact on familiality estimates with some catatonia phenotypes exhibiting substantial familial aggregation, which may inform about the most adequate phenotypes for molecular studies. From a familial-genetic perspective, the catatonia phenotype in psychotic and mood disorders has a transdiagnostic character.