Bones and Joints

The accumulation of undegraded GAG in connective tissues causes a wide range of musculoskeletal problems. Movement of joints, especially the knees, hips, and elbows, usually becomes restricted during the first few years of life, causing MPS VI patients to assume a flexed-knee, crouched stance (see photograph below). These individuals also develop the typical flexion contractures of the hand. Decreases in joint mobility are due to skeletal changes, contractures, and fibrosis of tendons, ligaments, and soft tissue.¹

A widespread constellation of skeletal abnormalities called dysostosis multiplex is diagnostic for MPS. The radiographic findings of dysostosis multiplex include the following:¹

• thickened calvarium, often with craniosynostosis
• a J-shaped sella turcica
• abnormal spacing of the teeth and odontoid dysplasia
• anterior hypoplasia of lumbar vertebrae with kyphosis
• ovoid and beaked vertebrae
• short and thick clavicles
• oar-shaped ribs with narrowing at the vertebral end and broadened sternal ends
• tilting of the radial and ulnar epiphyses
• long bones with enlarged diaphyses and irregular metaphyses
• a dysplastic pelvis with acetabular hypoplasia and small, flared iliac wings

The series of photos and radiographs below illustrate dysostosis multiplex in MPS VI.

		Altered Stance of MPS VI. A 30-year-old male with marked manifestations of MPS VI exhibits a flexed-knee, crouched stance typical of the disease. This altered stance reflects reduced joint mobility and widespread skeletal abnormalities.
		Dysostosis Multiplex—Skull. Radiography reveals dolichocephaly, thickened calvarium, and J-shaped sella turcica in a 13-year-old patient with MPS VI.2
		Dysostosis Multiplex—Ribs. Radiography reveals oarshaped ribs in a 13-year-old patient with MPS VI.2
		Dysostosis Multiplex—Spine. Radiography reveals typical "beaked" vertebrae in a 6-year-old patient with MPS VI.
		Dysostosis Multiplex—Spine. Radiography reveals gibbous deformity and ovoid vertebrae in an 18-month-old patient with MPS VI.
		Dysostosis Multiplex—Hand. Paired radiographs, taken in the same MPS VI patient at 18 months (top) and 7 years (bottom), reveal progressive development of short and wide phalanges, deformed carpal bones, and altered carpal angle.
		Dysostosis Multiplex—Pelvis. Radiography reveals increased acetabular angles and dysplastic femoral heads in a 6-year-old patient with MPS VI.

1. Neufeld EF, Muenzer J. The mucopolysaccharidoses. In: Scriver CR, Beaudet AL, Sly WS, Valle D, eds. The Metabolic and Molecular Bases of Inherited Disease. Vol 3. 8th ed. New York, NY: McGraw- Hill; 2001:3421-3452.
2. Maroteaux P, Leveque B, Marie J, Lamy M. [A new dysostosis with urinary elimination of chondroitin sulfate B]. Presse Med. 1963;71:1849-1852. French.