[Natural history of Morquio A disease]

Type IV mucopolysaccharidosis (Morquio A syndrome; MPS IVA; OMIM 253000), is a multisystemic, severe and very disabling disease, also life-threatening; MPS IVA is due to a deficiency of the enzyme N-acetylgalactosamine-6-sulfate sulfatase (GALNS), a lysosomal enzyme responsible for the degradation of keratan sulfate (KS) and chondroitin-6-sulfate (C6S). The disease is characterized by respiratory, pulmonary manifestations and also causes bone involvement with progressive spondyloepimetaphyseal degradation and mild and late-onset ophthalmologic, hearing and cardiac complications. These manifestations progressively impair the patients' physical mobility. Severe forms of the disease, diagnosed before the age of 1 year, can be distinguished from intermediary (diagnosed between 1 and 5 years old) and attenuated disease, diagnosed after the age of 5 years (occasionally far later). The main signs are bone deformities namely pectus carinatum, kyphoscoliosis and genu valgum, with early flattening of the growth curve, leading rapidly to almost complete growth arrest. Patients have normal cognitive development. The radiological signs are relatively specific with, in particular, platyspondyly, shortening of the long bones and characteristic pelvic changes. The diagnosis is suggested by elevated urinary GAGs level and profile, and is confirmed by GALNS enzymatic studies on molecular testing. Genetic counseling is important in this autosomal recessive disorder and enzymatic and/or molecular testing can be offered for prenatal diagnosis. Management is mostly symptomatic, based on early detection and orthopedic correction of spine and lower limb deformities, ENT and respiratory management and psychological, social and educational support for the child and his/her family.