Polymorphisms in regulator genes of GSH metabolic pathway have been described in CF, including Glutathione S-transferase P1 (GSTP1), GSTT1, GSTM1 and Glutamate-Cysteine Ligase, Catalytic Subunit (GCLC) genes, which have been associated with greater CF clinical severity [7,12,16-23]. The gene discussed is GSTM1; the disease is cystic fibrosis.