Approximately 3% of all PCs are associated with SDH deficiency (Gill et al. 2010b) and occur as part of PGL1 and PGL4; except for negative SDHB immunohistochemistry (discussed in detail below), these are otherwise histologically indistinguishable from sporadic PCs or from PCs associated with other heritable syndromes (e.g. multiple endocrine neoplasia type 2 (MEN2), VHL and NF). The gene discussed is SDHB; the disease is multiple endocrine neoplasia type 2.