What is Sclerosteosis?

It is a rare genetic syndrome. Most cases of the syndrome have been identified amongst the Afrikaner population in South Africa, but cases have also been reported in the USA and Brasil.

The syndrome leads to bone overgrowth which in turn causes a number of health issues and symptoms.

Sclerosteosis is the most severe form of the syndromes related to SOST-related sclerosing bone dysplasia.

Syndrome Synonyms:
Cortical Hyperostosis With Syndactyly Sost Truswell-Hansen disease Truswell-Hansen syndrome

What gene changes cause Sclerosteosis?

Changes in the SOST gene are responsible for causing the syndrome.

It is inherited in an autosomal recessive pattern.

What are the main symptoms of Sclerosteosis?

Bone overgrowth is a main symptom of the syndrome. This leads to the development of bones that are wider and denser than normal. This overgrowth affects the bones of the skull in particular.

Unique facial features of this syndrome, are for the most part caused by bone overgrowth. They include a large jaw, misaligned teeth, a sunken midface, bulging eyes and a prominent forehead.

Excessive bone overgrowth continues throughout the life of an affected individual, which at the same time alters their facial and skeletal features. Thicker than normal bones in the skull may cause extra pressure on the brain, which in some individuals triggers frequent headaches.

This excessive bone overgrowth can also affect the cranial nerves, these nerves extend from the brain to the head and neck. The pinching of these nerves can lead to paralyzed facial muscles, hearing and vision loss and a diminished or lost sense of smell.
In some instances excessive bone overgrowth can lead to issues that may be life threatening, if they compress on the part of the brain connected to the spinal cord.

How does someone get tested for Sclerosteosis?

The initial testing for Sclerosteosis can begin with facial analysis screening, through the FDNA Telehealth telegenetics platform, which can identify the key markers of the syndrome and outline the need for further testing. A consultation with a genetic counselor and then a geneticist will follow.

Medical information on Sclerosteosis

This is a distinct form of sclerosing bone dysplasia. Affected individuals are usually tall with a large head, a prominent forehead and a large mandible. Syndactyly of digits 2 and 3 can be seen, which may be either cutaneous or bony. There may be radial deviation of the terminal phalanges. Radiographs reveal increased density of the bones of the skull with enlarged frontal sinuses, enlarged sella turcica and sclerosis of the cranial foramina. The mandible becomes massively enlarged and there is usually hypodontia. In the spine the pedicles and laminae of the lumbar and sacral vertebrae show increased density, but the vertebral bodies are normal. The tubular bones are massive with cortical thickening and disturbance of modelling. Onset is after 5 years. Progressive cranial nerve palsies may lead to facial paralysis, deafness and optic atrophy. (However Beighton and Hamersma (1985) found that there was no visual loss due to optic nerve compression in a series of 45 patients). The condition is autosomal recessive and most cases have been described in individuals of Dutch ancestry, especially in the Afrikaner population of South Africa. Sugiura and Yasuhara (1975) reported a Japanese case and Bueno et al., (1994) a Spanish case. Beighton (1997) noted that some heterozygotes have widening of the calvarium with loss of distinction between the tables of the skull.
Balemans et al., (1999) mapped the gene to 17q12-q21 in the same region as van Buchem disease in the family reported by Paes-Alves et al., (1982) and the family reported by Stein et al., (1983).
Balemans et al., (2001) demonstrated nonsense mutations in the SOST gene coding for a novel secreted protein with a cystine-knot motif. Brunkow et al., (2001) also described a nonsense mutation near the amino terminus of the protein in Afrikaners and a splice mutation in an affected individual of Senegalese origin.
Hamersma et al., (2003) studied the course and complications in 63 affected individuals in South Africa, seen over a 38-year period. Thirty-four died during the course of the survey, 24 from complications related to elevation of intracranial pressure as a result of calvarial overgrowth. The mean age of death was 33 years, with an equal gender distribution. Facial palsy and deafness, as a result of cranial nerve entrapment, developed in childhood in 52 (82%). Mandibular overgrowth was present in 46 (73%) adults and syndactyly in 48 (76%).
Two sisters with novel homozygous frameshift mutations in the SOST gene were described by He et. al. (2016). They had syndactyly and increased bone density. The proband showed typical manifestations of generalized thickening of cranial vault and compression, whereas her sister only had exophthalmos.
Van Lierop et. al. (2017) reviewed 96 individuals with SOST-related conditions. Clinical characteristics were hearing loss (94%), facial palsy (93%), frontal bossing (90%), increased intracranial pressure (71%), and syndactyly (66%).

* This information is courtesy of the L M D.
If you find a mistake or would like to contribute additional information, please email us at: [email protected]

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