Congenital disorder of glycosylation type Ia (CDG-Ia1, recently named PMM2-CDG) is an inherited autosomal recessive rare disease caused by mutations in the phosphomannomutase 2 (PMM2) gene (1) and affected more than 800 patients worldwide in 2009 (calculated frequency 1:20.000 to 1:50.000 births) (2, 3). The gene discussed is PMM2; the disease is PMM2-congenital disorder of glycosylation.