Another study investigated the incidence of the null genotype (homozygous deletions resulting in absent enzyme activity) of glutathione-S-transferase M1 (GSTM1) in three Chinese minorities, Kazakh, Uygur, and Tajik that experience varying incidence of esophageal SCC in a high incidence area. Here, GSTM1 is linked to esophageal squamous cell carcinoma.