B4GALT1 and Peters plus syndrome: Deficiencies of beta1,3- and beta1,4-galactosyltransferases, particularly B3GALTL and B4GALT1, lead to neuronal phenotypes: B3GALTL deficiency, either by bi-allelic truncating mutations or by combination of genomic loss and point mutation, causes Peters Plus syndrome (MIM261540), an autosomal recessive syndrome with multiple symptoms including psychomotor retardation [27].