Homozygosity for the variant alpha-L-fucosidase trait and mucolipidosis III.

The variant alpha-L-fucosidase genotype, phenotypically observed as a low plasma level of alpha-L-fucosidase in healthy individuals, can modify the plasma expression of the primary genetic defect in mucolipidosis III. Three patients with clinical, radiological, and biochemical features of mucolipidosis III, had a normal plasma level of alpha-L-fucosidase activity. The thermostability curves for the plasma alpha-L-fucosidase from these patients and the plasma alpha-L-fucosidase of the parents of one of them, are discussed to support the suggestion that they are homozygous for the autosomal recessive variant alpha-L-fucosidase trait. From a practical point of view, these observations warn against the use of the plasma alpha-L-fucosidase assay as a screening test for mucolipidoses.