SDHD and pheochromocytoma: The SDHD His50Arg and Gly12Ser variants have previously described neuroendocrine tumors such as pheochromocytomas and paragangliomas, as well as midgut carcinoids and Merkel cell carcinomas (Cascon et al. 2002b, Kytola et al. 2002, Perren et al. 2002, Ni et al. 2008).