Paternal uniparental isodisomy of chromosome 22 in a patient with metachromatic leukodystrophy.

Metachromatic leukodystrophy (MLD) is an autosomal recessive lysosomal storage disease caused by deficiency of the enzyme arylsulfatase A encoded by the ARSA gene located on 22q13.33. Typically, in autosomal recessive disease, a patient inherits two mutations from both parents who are heterozygous carriers. However, in some instances, it is possible to develop the disease by uniparental isodisomy (UPiD), in which two copies of the same mutated allele are inherited from only one carrier parent. Here, we report the first patient with MLD caused by UPiD of chromosome 22. The patient has a homozygous missense mutation, P136T, on ARSA. Family study of the ARSA gene and leukocyte enzyme activity revealed that his father and sister were heterozygous carriers, but his mother possessed only wild-type alleles and normal enzyme activity. Karyotypes of the patient and the parents were normal. Microsatellite analysis showed no discrepancy of parentage, and paternal UPiD of chromosome 22 was indicated. Finally, genome-wide single-nucleotide polymorphism array confirmed the region of UPiD was extended to the entire chromosome 22 of the patient.