Patients with one or two copies of the HLA-B*59:01:01:01 allele may have an increased risk of severe cutaneous adverse reactions, such as Stevens-Johnson Syndrome and toxic epidermal necrolysis, when treated with methazolamide as compared to patients with no HLA-B*59:01:01:01 alleles or negative for the HLA-B*59:01:01:01 test. Other genetic and clinical factors may also influence risk of methazolamide-induced adverse reactions.