MAX and hypophosphatasia: Four genes required for appropriate assembly and function of SDH include SDHAF2, SDHB, SDHC, and SDHD. Hereditary paraganglioma-pheochromocytoma syndrome (HPP) is a tumor predisposition syndrome caused by germline heterozygous pathogenic variants in SDHAF2, SDHB, SDHC, SDHD, MAX, SDHA, and TMEM127. HPP is inherited in an autosomal dominant manner in all genes except for SDHD and SDHAF2 which are maternally imprinted (Else et al., 2008).