Mn blood groups and bipolar disorder: evidence of genotypic association and hardy–weinberg disequilibrium

Background: MN blood groups have been studied in the past as a genetic marker of bipolar disorder (BD). Several previous studies reported an association of the illness with lower frequency of blood group NN. Methods: We analyzed distribution of MN blood groups in a sample of 174 patients with BD, 176 with unipolar depression, 98 with schizophrenia, and 331 healthy controls. In addition, we tested whether the inferred genotypes conform to Hardy–Weinberg equilibrium (HWE). Results: The frequency of NN phenotype was significantly lower among the bipolar patients than in any of the other three groups (p< .001). The genotype frequencies in the BD group deviated significantly from those expected under HWE (p< .01). Conclusions: These results suggest a possible locus on chromosome 4 (4q28–q31.1) associated with genetic susceptibility to bipolar illness.