Recent studies found an association between the psychotic phenotype of bipolar (BP) disorder and the G72/G30 gene. As the psychotic features are considered a promissing phenotypic trait that might enhance the chance of identifying the genes underlying the BP, we tried to estimate the heritability of psychotic features in connection with the parent-of-origin and proband /affected relative gender.

244 unilineally affected families in which the proband had relatives diagnosed with BP, schizoaffective disorders, schizophrenia, recurrent MDD-UP were selected from our sample of 376 families ascertained through a BP-I proband from consecutive hospital admissions without regard to familial psychopathology. The data were analysed with SAGE 5.4-software (ASSOC and FCORR) (Elston et al, 2007).

In the total familial sample the sex of the affected individuals significantly influenced the total variance of the PSYCHOSIS-liability. Females were more prone to PSYCHOSIS (OR=1.64, 95%CI=1.47-1.65) being 2-times more frequently psychotic than males. The parent-of-origin did not influence the variance of PSYCHOSIS-liability (p=0.75). Nevertheless in families with paternal (PAT) transmission (N=133) the heritability of PSYCHOSIS was higher than in maternal (MAT) families (N=111) . (11.56% versus 6.86%). In PAT families the parent-offspring transmission was significant (p=0.046), while the sibling effect (that includes parent-offspring correlation and environmental influences) was not significant (p=0.22). In MAT families the parent-offspring transmission was not significant (p=0.41), while the sibling effect was significant (p=0.0022).

Our data show that sex and parent-of-origin may modify the liability to psychotic BP. Genetic factors seem to be stronger in PAT families.