PMM2 and PMM2-congenital disorder of glycosylation: PMM2 (OMIM #601785) encodes phosphomannomutase 2, a key enzyme involved in N‐glycosylation and bi‐allelic pathogenic coding variants in PMM2 cause congenital disorder of glycosylation type 1a (CDG1a) (OMIM #212065), a multi‐system disorder which invariably includes neurological impairment and typically an abnormal transferrin isoelectric focusing test (Andreotti et al., 2015; Noreau et al., 2014; Sparks & Krasnewich, 2015; Westphal et al., 2001).