No evidence of increased risk for schizophrenia or bipolar affective disorder in persons with aneuploidies of the sex chromosomes

Background. Several case reports and reviews have suggested an increased in cidence of schizophrenia or bipolar disorder among persons with sex chromos ome aneuploidies, but this observation may have been caused by biased sampl ing. Methods. The 1122 individuals with sex chromosome aneuploidies registered i n the Danish Cytogenetic Central Register were screened in the Danish Psych iatric Central Register for admissions with schizophrenia or bipolar affect ive disorder, Both registers are population based and have existed since 19 68 and 1969 respectively. Relative risks were calculated for schizophrenia, bipolar affective disorder and either schizophrenia or bipolar disorder co mbined as one phenotype. Since hospitalization for a psychiatric disorder i ncreases the probability that a cytogenetic examination is performed, the r elative risks could be inflated, and they were therefore adjusted according ly. Results, Aneuploidies of the X or Y chromosomes were not associated with an increased risk of schizophrenia or bipolar disorder. The occurrence of the combined phenotype including both schizophrenia and bipolar disorder was s ignificantly reduced among persons with Turner's syndrome and significantly increased among individuals with the 47, XYY karyotype. Conclusions. This population-based study did not find evidence supporting t he presence of risk alleles for schizophrenia or bipolar disorder on the X chromosome or the pseudoautosomal region on the Y chromosome. The findings of an increased risk for the combined phenotype to XYY males and the reduce d risk for persons with Turner's syndrome are interesting but difficult to explain with present neurobiological knowledge and inconsistent with the ot her findings of the study.