PHF8 belongs to the family of ferrous iron and 2-oxoglutarate dependent oxygenases, and is active as a histone lysine demethylase with selectivity for the di-and monomethyl states.
Mutations in PHF8 cause Siderius type X-linked mental retardation (XLMR). In addition to moderate mental retardation, features of the Siderius-Hamel syndrome include facial dysmorphism, cleft lip and/or cleft palate, and in some cases microcephaly. A chromosomal microdeletion on Xp11.22 encompassing all of the PHF8 and FAM120C genes and a part of the WNK3 gene was reported in two brothers with autism spectrum disorder in addition to Siderius-type XLMR and cleft lip and palate.