Among the 95 patients analyzed (70% female; median age: 23 years; 19% with syndromic GIST), three molecular subtypes were defined: 11 had SDH competency (which included mutations in NF1; BRAF; other rare mutations/fusions; or no identified), and 84 had SDH deficiency (75% due to SDH mutations and 25% due to SDHC promoter hypermethylation). The gene discussed is SDHB; the disease is gastrointestinal stromal tumor.