Clones of skin fibroblasts from normal individuals, patients with different mucopolysaccharidoses, and certain of their relatives have been examined for cellular metachromasia and cellular uronic acid.

All the clones derived from affected individuals and heterozygous carriers in families with the autosomal forms of Hurler's syndrome showed marked metachromasia and increased cellular uronic acid. Since only one cell population was demonstrated in clones derived from heterozygous carriers, no evidence for autosomal inactivation was obtained.

Clones derived from affected individuals with the X-linked recessive form of Hurler's syndrome contained uniform populations of metachromatic staining cells which demonstrated increased cellular uronic acid. Clones derived from the noncarrier fathers showed no cellular metachromasia or increased cellular uronic acid. Clones derived from the heterozygous mothers and sisters showed two populations both qualitatively and quantitatively. On the average, 72% of these clones were metachromatic and demonstrated an increased uronic acid content; 28% of the clones showed no metachromasia and the uronic acid content was similar to that found in normal individuals.

The appearance of two distinct cell populations in clones derived from females heterozygous for the X-linked recessive form of Hurler's syndrome provides evidence in favor of the Lyon hypothesis.

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