Ethnic differences in distributions of GSTM1 and GSTT1 homozygous "null" genotypes in India.

We estimated the frequencies of GSTM1 and GSTT1 "null" homozygotes in 10 different ethnic populations of India by a genotyping method based on polymerase chain reaction. These populations, inhabiting diverse geographical locations and occupying various positions in the sociocultural hierarchy, were represented by a sample of 299 unrelated individuals. Frequencies of GSTM1 and GSTT1 "null" homozygotes varied from 20% to 79% and 3% to 39%, respectively, across the study populations. Maximum frequencies of GSTM1 and GSTT1 "null" homozygotes (79% and 39%, respectively) have been observed in the same population (Jamatia). Frequencies of homozygous "null" genotypes at the GSTM1 and GSTT1 loci show a significant positive correlation in these populations, which is contrary to expectations. A possible implication is that the two enzymes are working in tandem, instead of working in a complementary way.