[Hunting the susceptibility gene for psychosis: a study of a family overloaded with schizophrenia and bipolar disorder]

Abstract

Objective: It is a long-standing debate whether schizophrenia and bipolar disorder are separate clinical entities or different poles on a spectrum. In this paper we present a family overloaded with schizophrenia, and schizoaffective, bipolar and unipolar disorders. Common loci for bipolar affective disorder and schizophrenia were tested by linkage analysis.

Method: The pedigree of an index family which had been followed by our department for nearly 20 years was extended. The index family members were diagnosed by two psychiatrists with two distinct structured interview schedules (SCID-I and SADS-L). A field visit was undertaken for the evaluation of the extended family (n= 40) and SADS-L was used for psychiatric assessment. Blood samples were collected for molecular studies. A linkage study has been performed for overlapping susceptibility regions for schizophrenia and affective disorders (10p13-p12, 13q32, 18p and 22q11-q13) and a locus (20p11.2-q13) to which a linkage had been shown in a bipolar family who lived in the same region. Both autosomal recessive and dominant mode of inheritance were assumed in the analysis.

Results: The pedigree consisted of 108 individuals of whom 23 are affected. All affected subjects presented psychotic features except for 5 unipolar patients. The pedigree was reconstructed with respect to psychosis phenotype. Further linkage and haplotype analysis excluded all five loci on chromosomes 10, 13, 18, 20 and 22 under both autosomal dominant and recessive modes of inheritance assumption.

Conclusion: A potential linkage between the psychosis gene and reported susceptibility loci overlapping in bipolar affective disorder and schizophrenia was not demonstrated Genome-wide analysis should be performed.