Atypical presentation of mucopolysaccharidosis type IVA

A 14 year old patient with short stature, type I diabetes, and cataracts was referred for evaluation of avascular necrosis of the femoral head. Radiography was suggestive of spondyloepiphyseal dysplasia with decreased bone mineral density for age. Targeted molecular and biochemical testing were normal in this patient. Whole exome sequencing was performed and showed compound heterozygosity for previously reported pathogenic GALNS variants which were diagnostic of mucopolysaccharidosis, type IVA (Morquio A). While this case describes neither a novel condition nor a new mutation, it does illustrate three important points in the diagnosis of patients with atypical forms of MPS IVA. First, that in many instances urine glycosaminoglycan analysis is not sufficient to rule out MPS IVA as a potential diagnosis. Patients in whom biochemical screening is advised should have measurement of leukocyte enzymatic activity. Second, that in patients with radiographic evidence of spondyloepiphyseal dysplasia with additional features or with normal targeted testing, MPS IVA should remain in the differential diagnosis. Third, that whole exome sequencing represents a viable diagnostic platform for evaluation of patients with unknown skeletal or metabolic disease.