Analysis of genome-wide CAG CTG repeats, and at SEF2-1B and ERDA1 in schizophrenia and bipolar affective disorder

A shift towards larger CAG/CTG triplet repeats and schizophrenia (SCZ) and bipolar affective disorder (BPAD) has been detected by several recent studi es, using the Repeat Expansion Detection (RED) technique, however no specif ic loci have been shown to be responsible for this shift. Further analyses by our group of RED (CTG),, ligation products amongst an extended sample of patients and comparison with controls matched for age, sex and ethnicity s how no significant differences in distribution (P = 0.23, n = 95; P = 0.93, n = 91, for SCZ and BPAD respectively). Alleles at two recently discovered unstable trinucleotide repeat loci at 13q21.1 (SEF2-1B) and 17q21.3 (ERDA1 ) have also been analysed in affecteds and matched controls, We observed no increase in frequency of larger alleles (>37 repeats) in affected individu als at SEF2-1B (BPAD: P = 0.95, n = 100; SCZ: P = 0.61, n = 97) or at ERDA1 (BPAD: P = 0.4, n =101; SCZ: P = 0.05, n = 151, with larger alleles more f requent in controls). Our findings suggest that larger CAG/CTG repeats at t hese loci ape neither major contributory factors to the etiology of psychos is, nor in linkage disequilibrium with a gene that is. Furthermore, when th e RED results were compared to allele sizes at SEF2-1B and ERDA1, it was ob served that a majority of SCZ, BPAD and control individuals with large RED products had a large allele at either or both sites (78% for RED products g reater than or equal to 270 bp; 62% for RED products greater than or equal to 180 bp).