SDHD and microcephaly 1, primary, autosomal recessive: The SDHx hereditary PGL/PCC syndromes are relatively newly described entities that involve a mutation in SDHA, SDHB, SDHC, SDHD, or SDHAF2. In 2000, the first report was published of an association of one of the SDHx genes with hereditary PGL/PCC syndromes (21).