Too Much Bone The Middle Ear in Sclerosing Bone Dysplasias

Herman Hamersma, Louis Hofmeyr Florida, South Africa

Abstract

The middle ear changes in Sclerosteosis and Van Buchem disease are described. Reduced bone resorption occurs due to faulty activity of the sclerostin molecule, a product of the recently discovered SOST gene in chromosome 17. Syndactyly draws attention to sclero-teosis, and a conductive hearing loss develops before age six in both conditions. Acute, repeated attacks of facial palsy, similar to Bell's palsy, are usually the first symptoms in both conditions. Total facial nerve decompression can stop the attacks of facial paralysis. The hearing loss is a problem because new bone formation continues up to age 21. Life saving craniectomy becomes necessary when increased intracranial pressure develops, and this may have to repeated. The sclerostin molecule is now of major interest to the researchers who want to develop a treatment for osteoporosis.

Copyright © 2007 S. Karger AG, Basel

Sclerosing bone dysplasias are rare genetic disorders of bone remodeling. Only a few cases were published before X-rays were discovered. In 1904, Albers-Schonberg, professor of radiology in Hamburg (who later died from overexposure to radiation), published the X-rays of a patient who had very strong hard bones and a very thick skull. The terms 'marble bone disease' and 'osteopetrosis' then came into use until the various genetic syndromes were identified and new names given. The case of Albers-Schonberg was identified as rare, benign, dominant osteopetrosis. 'Malignant' recessive osteopetrosis occurs more often and children rarely survive for more than a few years. This presentation deals with sclerosteosis, a relatively benign form of excessive bone formation of which 67 cases have been identified in the Afrikaner community in South Africa (from Dutch, French and German descent) and 30 cases in the rest of the world [1]. Van Buchem disease, of which less than 30 cases have been identified, is very similar and occurs mostly in Holland (figs. 1-5) [2].

Sost Related Sclerosing Bone Dysplasias
Fig. 1. A case with Van Buchem disease (from the thesis of Van der Wouden [2]).
Sost Related Sclerosing Bone Dysplasias
Fig. 2. A case with Van Buchem disease (from the thesis of Van der Wouden [2]).

Craniometaphyseal dysplasia and Camurati-Engelmann disease are even less common but show similar involvement of the skull and middle ears. The term 'marble bone disease' is now only used as a nonspecific collective name for the skeletal dysplasias with dense bones, especially sclerosteosis and Van Buchem disease.

Slerosteosis
Fig. 3. The skull base of a normal skull (a) and from a patient with Van Buchem disease (b). The foramen magnum and exit foramina of nerves are affected. See the thesis of Van der Wouden [2].
Slerosteosis

The SOST gene, which is involved in sclerosteosis and Van Buchem disease, was discovered a few years ago on chromosome 17. Bone metabolism researchers are very excited about this discovery, and are researching the characteristics of this gene in order to develop a treatment for osteoporosis. Patients suffering from sclerosing bone dysplasias sincerely hope that one day it may also become possible to treat excessive bone formation, because their thick bones not only press on the brain and sometimes cause premature death, but

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