Genotypes and phenotypes of Sri Lankan Patients with Mucopolysaccharidosis type IVA

Abstract

Mucopolysaccharidosis type IVA is a rare autosomal recessive lysosomal storage disorder occurring worldwide in all ethnic groups. It is caused by biallelic variants in the GALNS gene (OMIM 612222). We report five cases of mucopolysaccharidosis type IVA with short stature and severe skeletal dysplasia. An optimized diagnostic strategy that combined enzymatic testing and genetic screening was applied. All the tested urine samples showed increased urinary glycosaminoglycan / creatinine ratios. In all five cases, the enzyme activity of galactosamine-6-sulfate sulfatase was pathologically decreased. Gene-targeted sequencing revealed a previously unreported homozygous c.139-12T>C variant of the GALNS gene in one patient and three previously reported missense variants in four patients; c.253T>C (p.Cys85Arg), c.626C>T (p.Ala209Val) and c.878C>T (p.Ser293Leu). Genetic studies not only confirm the diagnosis of mucopolysaccharidosis IVA, but also enable predicting the prognosis and facilitate genetic counseling. Enzyme replacement therapy is not available in Sri Lanka to date. However, the quality of life in these patients can be improved by a multidisciplinary approach.