Synonyms:FLJ12768, GPI mannosyltransferase 4, GPI mannosyltransferase IV, GPI MT IV, hSMP3, PIG Z, PIGZ, SMP3, SMP3 homolog Background:Mannosyltransferase involved in glycosylphosphatidylinositol-anchor biosynthesis. Transfers a fourth mannose to some trimannosyl-GPIs during GPI precursor assembly. The presence of a fourth mannose in GPI is facultative and only scarcely detected, suggesting that it only exists in some tissues.