Alpha 1,3/1,6 mannosyltransferase ALG2 (ALG2) is a bifunctional mannosyltransferase normally tranfers a mannose moiety to the lipid linked oligosaccharide (LLO aka N glycan precursor) which is required for subsequent N glycosylation of proteins. Defects in ALG2 can cause congenital disorder of glycosylation 1i (ALG2-CDG, previously known as CDG1i; MIM:607906), a multisystem disorder characterised by under glycosylated serum glycoproteins. CDG type 1 diseases result in a wide phenotypic spectrum, from poor neurological development, psychomotor retardation and dysmorphic features to hypotonia, coagulation abnormalities and immunodeficiency (Thiel et al. 2003). Defect in ALG2 can also cause congenital myasthenic syndrome (ALG2-CMS), which is due to a defect in neuromuscular signal transmission (Cossins et al. 2013). The most commonly affected muscles include proximal limb muscles. Mutations causing ALG2-CMS include p.V68G and p.72_75delinsSPR (Cossins et al. 2013).