CAG/CTG repeat polymorphisms on chromosomes 12q, 17q and 18q in schizophrenia and bipolar disorder in the Portuguese population

Several recent studies have reported anticipation in both schizophrenia and bipolar disorder, suggesting the hypothesis that a trinucleotide repeat-containing gene may be etiologically related to these diseases. There is evidence of enlarged CAG/CTG repeats in subjects affected with schizo-phrenia or bipolar disorder. Thus genes containing CAG/ CTG repeats may be etiologic candidates. In an attempt to identify the specific expanded CAG/CTG locus or loci which are associated with schizophrenia and bipolar disorder, we have analyzed several unstable trinucleotide repeat loci at 12q24.1 (SCA2), 17q21.3 (ERDA1) and 18q21.1 (SEF2-1B) in 23 bipolar families (n=144) and 31 schizophrenia families (n=138) from the highly homogeneous Portuguese population. We observed no increase in frequency of larger alleles in affected individuals at SCA2, ERDA1 and SEF2-1B, except one bipolar family which showed large expansions at the SEF2-1B locus. In addition, no significant differences between the patients and the control groups. We concluded that larger CAG/CTG repeats at these loci are not major contributory factors to the etiology of schizophrenia or bipolar disorder, at least in the Portuguese population studied.