The ALG6(F304S) variant is not as efficient at complementing ALG6-deficient yeast as the wild type allele [38], but is not thought to cause CDG because it occurs in 27–33 % of the population, and 4–6 % of the population are homozygous for this variant [37, 39, 40]. This evidence concerns the gene ALG6 and congenital disorder of glycosylation.