Sclerosteosis 2

A number sign (#) is used with this entry because of evidence that sclerosteosis-2 (SOST2) is caused by heterozygous or homozygous mutation in the LRP4 gene (604270) on chromosome 11p11.

Description

Sclerosteosis is a severe sclerosing bone dysplasia characterized by progressive skeletal overgrowth. Syndactyly is a variable manifestation. The disorder is rare and the majority of affected individuals have been reported in the Afrikaner population of South Africa (summary by Brunkow et al., 2001).

For a discussion of genetic heterogeneity of sclerosteosis, see SOST1 (269500).

Clinical Features

Bueno et al. (1994) described a 17-year-old Spanish patient with sclerosteosis. He presented at age 12 years with right facial nerve palsy; examination revealed facial asymmetry due to the palsy, mild frontal bossing, midface hypoplasia, dental malocclusion, and marked prognathism. Bilateral 3-4 syndactyly of fingers and toes was observed at birth; in addition, the distal phalanges of some fingers were short and radially deviated, with hypoplastic nails. Radiographic findings included a widened and uniformly sclerotic calvarium with a very dense base, prominent vascular markings, expanded sella turcica, enlarged frontal sinuses, enlarged sclerotic mandible, widened and dense clavicles and ribs, and sclerotic vertebral endplates and pedicles. All long bones were involved and showed cortical hyperostosis with moderate alteration of external contours. There was bilateral 3-4 bony syndactyly of the fingers, with shortening and radial deviation of several distal phalanges; no skeletal anomalies of the toes were seen. At 17 years of age, his height was above the 97th percentile, and his head circumference was greater than the 98th percentile. He had no symptoms other than the mild right facial palsy; specifically, he had no hearing impairment or signs of increased intracranial pressure. Bueno et al. (1994) stated that the patient had no known Dutch ancestry and that this was the first reported case of sclerosteosis in an individual of Mediterranean origin.

Itin et al. (2001) reported a 36-year-old woman of Greek origin who had finger and nail dysplasia and facial asymmetry since birth. Examination due to increasing spastic and ataxic gait disturbances revealed hypertelorism and a broad facial appearance, with cranial nerve disturbances including bilateral peripheral facial nerve palsy and hearing loss related to bony narrowing of the cranial nerve foramina, and spastic-ataxic tetraparesis. The patient had bilateral hypoplasia of the index fingers, and nails were dysplastic and separated into 2 parts, particularly on the index fingers. Radiologic evaluation showed hyperostosis of the skull, with 3.5-cm thick cortical bone by CT scan; x-rays of the hands and legs showed hyperostotic cortical thickening. Itin et al. (2001) stated that the syndactyly/brachyphalangy with nail dysplasia was characteristic and should be recognized as a marker for sclerosteosis.

Molecular Genetics

In a Spanish man and an unrelated woman of Greek origin with sclerosteosis, originally reported by Bueno et al. (1994) and Itin et al. (2001), respectively, Leupin et al. (2011) identified heterozygosity and homozygosity for missense mutations in the LRP4 gene (604270.0009-604270.0010). Leupin et al. (2011) noted that although both patients exhibited the typical sclerosteosis features of finger syndactyly, facial asymmetry, and cortical thickening of the skull and long bones, the heterozygous Spanish patient had only mild facial palsy, whereas the homozygous Greek patient had more severe neurologic complications that included hearing loss and spastic-ataxic tetraparesis.