Genotype-phenotype correlations revealed notable findings: variants in the N-terminus of ALG2 before the intramembrane domain were associated with congenital myasthenic syndromes (CMS), whereas those in the C-terminus caused ALG2-CDG; DPM2-CDG patients with variants in transmembrane region 1 exhibited more severe phenotypes; male patients with hemizygous variants in SLC35A2 demonstrated milder phenotypes compared to those with mosaic variants. Here, ALG2 is linked to congenital myasthenic syndrome.