PMM2 and congenital disorder of glycosylation: Phosphomannomutase 2 - Congenital Disorder of Glycosylation (PMM2-CDG, formerly CDG Ia, ORPHA79318, MIM 212065) is by far the most frequent type of CDG with more than 800 patients reported worldwide in 2009 [3] (about 1:20.000 to 1:50.000 births worldwide).