The GSTM1 gene encodes glutathione S-transferase M1, a member of the GST family of enzymes. These enzymes have broad detoxifying abilities against carcinogens, drugs, or other toxins.
Although there are a few SNPs in the GSTM1 gene, the main polymorphism of interest is the null allele - in other words, some individuals are lacking one or even both copies of the GSTM1 gene. Individuals with fewer copies of GSTM1 may be somewhat more prone to allergies, asthma, and certain cancers, especially if they are missing copies of other GST family genes such as GSTP1 or GSTT1.
[PMID 18303971] While testing for null alleles seems sufficient for Caucasians and Oriental subjects, the most promising target SNPs for GSTT1 association studies in African-American and Hispanic subjects may be those causing the amino acid changes Asp43Asn, Thr65Met, Thr104Pro and the single nucleotide deletion in exon 4.