Mucopolysaccharidosis Type VI: a Predominantly Cardiac Phenotype Associated with Homozygosity for P.R152W Mutation in the ARSB Gene

Mucopolysaccharidosis type VI (MPS VI) is a rare lysosomal, autosomal recessive storage disorder caused by deficient activity of N-acetylgalactosamine-4-sulfatase (ARSB). Approximately, 140 ARSB gene mutations have been identified; however, most are private mutations making genotype-phenotype correlation for most MPS VI patients difficult. The aim of this study was to describe the natural clinical course in patients homozygous for the p.R152W mutation from eight unrelated families. From our database of 70 patients with MPS VI, we selected 10 patients homozygous for the p.R152W mutant allele (median age 27.5 years, range 18-38 years). We performed a cross-sectional observational study characterizing the onset and prevalence of clinical manifestations. First signs of the disease, such as cardiac valve disease, slightly decreased joint range of motion and mild growth retardation, were observed in mid-adolescent years (median 15 years). Within the disease course, the most common clinical feature in all the patients was progressive heart disease of predominantly valve origin leading to symptoms of heart failure. Other typical MPS VI features were subtle and not present in all the patients. Delays up to 23 years (median 8.5 years) intervened between symptom onset and disease diagnosis. Patients homozygous for the p.R152W mutation present a cardiac variant of MPS VI characterized by progressive cardiac valve disease leading to serious cardiac complications including abrupt death due to cardiac failure.