Assessment of skeletal status in patients with congenital disorder of glycosylation type IA

Abstract

Congenital disorder of glycosylation (CDG) type IA (phosphomannomutase deficiency) is the most common of a group of inherited metabolic disorders that are due to defective glycosylation of glycoproteins. CDG-IA is clinically characterized by major nervous system involvement and various organs are affected to a variable degree. Common clinical findings are skeletal changes including peculiar thoracic deformity and joint restriction, while a major radiological feature is diffuse osteopenia. The aim of this study was to measure bone density and biochemical markers of bone turnover in three patients with CDG-IA, whose age ranged between 14 and 27 years. We found that bone mass, as judged by standard densitometry, quantitative computed tomography and ultrasonography, was lower in patients than in age- and sex-matched healthy controls. Biochemical indexes of bone resorption including free pyridinoline levels in serum and pyridinoline and deoxypyridinoline urinary excretions were normal, whereas bone formation markers (serum osteocalcin and serum bone-specific alkaline phosphatase) activity were increased. These results suggest that low bone density is a component of CDG-IA, which should be considered among inherited metabolic diseases with decreased bone mass. We hypothesize that hypoglycosylation of noncollagenous bone proteins may contribute to the osteopenia observed in these patients. From a clinical point of view, our observation shows that bone density measurements can provide a quantitative assessment of bone involvement in such diseases.