A Novel Pathological ARSB Mutation (c.870G>A; P.Trp290stop) in Mucopolysaccharidosis Type VI Patients

Abstract

Mucopolysaccharidosis (MPS) type VI, also known as Maroteaux-Lamy syndrome, is a lysosomal storage disorder, characterized by the deficiency of the arylsulfatase B enzyme. The clinical phenotype and severity of the illness varies according to the residual enzyme activity. Typical features are a short stature, shortened trunk, protuberant abdomen, flexed-knee stance, arched back, corneal clouding, joint stiffness and contractures as well as a waddling gait. Patients typically have Hurler-like dysmorphic facial features: microcephaly, prominent forehead and eyes, a broad nose, low nasal bridge, thick lips, and hyperplastic gums with widely spaced teeth. Complications of the illness include obstructive airway, cardiac valvular problems, splenomegaly, hernias, and pneumonia. Unlike other MPS diseases, MPS VI is characterized by normal intellectual development. Since the disease is due to deficient glycosaminoglycan (mucopolysaccharide) metabolism, elevated urinary glycosaminoglycan levels are a main indicator of MPS. Diagnosis is confirmed by enzyme assays, specifically low arylsulfatase B activity in conjunction with the normal activity of other lysosomal enzymes. Enzyme replacement therapy and hematopoietic stem cell therapy are showing positive results in the management of the condition. The more severely affected patients, with a rapidly advancing form of the disease, have a short life span and succumb, most commonly to heart failure, by early adulthood. The frequency of ARSB variants in patients with MPS VI are as follows: 59.5% missense, 13.5% small deletions, 12% nonsense, 5% splice site or intronic variants, 3% small duplications, 3% large deletions, and 1% stop-loss. We report an Albanian family with siblings diagnosed with MPS Vl after clinical examination, biochemical tests, and molecular analysis. Hereby, a novel c.870G>A nonsense homozygous mutation was found responsible for the loss of the enzyme activity.