SDHB and gastrointestinal stromal tumor: SDHA/B/C/D deficiency GIST may be caused by a germline inactivating mutation in the suppressor genes encoding the SDH complex (SDHA, SDHB, SDHC and SDHD subunits) or by SDHC promotor-specific CpG island hypermethylation (SDHC epimutation) [5].