SDHB and gastrointestinal stromal tumor: While it is important to consider that the overall frequency of SDHA mutations in GIST is low given that SDH deficiency is seen in only ∼8% of all gastric GISTs (Miettinen et al., 2011), mutations in the SDHA subunit alone may be as common as mutations in all other subunits combined (Miettinen et al., 2012).