A study of linkage disequilibrium between polymorphic loci for monamine oxidases A and B in schizophrenia

Two X-linked microsatellites, (AC) n repeats at the monoamine oxidase (MAO)-A locus and (TG)n repeats at the MAO-B locus, were studied in 140 unrelated Caucasian male patients with schizophrenia and 91 unrelated Caucasian male controls. Among these subjects, we totally typed out nine alleles for the (AC) n repeats and eight alleles for the (TG) n repeats by using a PCR-based procedure. Allelic frequencies of either (AC) n repeats or (TG) n repeats were not found to be significantly different between patients and controls. However, a significant excess of the (AC)18/(TG)23 haplotype with a relative risk of 4.05 (95%; CI 1.15-14.26) was observed in patients with schizophrenia (Fisher's P = 0.011). The coefficient of linkage disequilibrium (delta) for the (AC)18/(TG)23 haplotype was 0.019 in schizophrenic patients and -0.046 in control subjects, respectively. The latter reached statistical significance (chi 2 = 6.02; df = 1; P < 0.02). The present findings suggest that linkage disequilibrium between polymorphic loci for human MAO-A and MAO-B may be associated with schizophrenia, and the (AC)18/(TG)23 haplotype may render an individual more vulnerable to such an illness.