The T911C (F304S) substitution in the human ALG6 gene is a common polymorphism and not a causal mutation of CDG-Ic.

A T911C (F304S) substitution in the ALG6 gene involved in congenital disorder of glycosylation type Ic (OMIM 603147) has been described. However, whether the F304S substitution is a common polymorphism or a causal mutation remains unclear. We screened for the T911C substitution in the ALG6 gene in 54 unrelated healthy French individuals. We developed a restriction fragment length polymorphism assay with a mutagenic primer introducing a diagnostic DdeI restriction site. We found 23 heterozygotes (42.6%) and 3 homozygous individuals (5.5%). This result indicates that T911C is a common polymorphism with an allele frequency of 27% in a French population and not a causal mutation of congenital disorder of glycosylation type Ic.