Background: MN blood groups have been studied in the past as a genetic marker of biopolar 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.