New mutations in two Dutch patients with early infantile galactosialidosis.

ABSTRACT

Galactosialidosis is an autosomal recessive lysosomal storage disease caused by a combined deficiency of lysosomal beta-galactosidase and neuraminidase as a result of a primary defect in the protective protein/cathepsin A (PPCA). We report the first 2 Dutch cases of early infantile galactosialidosis, both presenting with neonatal ascites. The defect was identified in urine, leukocytes, and fibroblasts. Residual activity was determined with a modified assay for cathepsin A and was <5% in leukocytes and <1% in fibroblasts. Histological examination of the placenta in case 1 showed extensive vacuolization in all cell types. Northern blot analysis of RNA isolated from the patients' cultured fibroblasts showed substantially decreased levels of the PPCA transcript, which nevertheless had the correct size of 2 kb. Mutation analysis of both mRNA and genomic DNA from the patients identified two novel mutations in the PPCA locus. Case 1 was a compound heterozygote, with a single missense mutation in one allele, which resulted in Gly57Ser amino acid substitution, and a single C insertion at nucleotide position 899 in the second allele, which gave rise to a frame shift and premature termination codon. Case 2 was homozygous for the same C899 insertion found in case 1.