To define the phenotypic heterogeneity among individuals harbouring MYMK variants, MYMK exons and flanking intron-exon boundaries were sequenced in >300 additional probands with congenital facial weakness who were referred with the following diagnoses: CFZS (1 proband); congenital myopathy with predominant facial weakness with micro/retrognathia (∼10 probands); isolated or syndromic congenital facial weakness and normal eye movements (∼50 probands); and Moebius syndrome (∼250 probands). Here, MYMK is linked to congenital myopathy with cores.