A dysostosis is a disorder of the development of bone, in particular affecting ossification. Examples include craniofacial dysostosis, Klippel–Feil syndrome, and Rubinstein–Taybi syndrome. It is one of the two categories of constitutional disorders of bone (the other being osteochondrodysplasia). When the disorder involves the joint between two bones, the term synostosis is often used. References


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Many mutations are responsible for DMD, and some have not been identified, so genetic testing may be falsely negative if the suspected mutation in the mother has not been identified.Prior to invasive testing, determination of the fetal sex is important; while males are sometimes affected by this X-linked disease, female DMD is extremely rare. This can be achieved by ultrasound scan at 16 weeks or more recently by free fetal DNA (cffDNA) testing. Chorion villus sampling (CVS) can be done at 11–14 weeks, and has a 1% risk of miscarriage. Amniocentesis can be done after 15 weeks, and has a 0.5% risk of miscarriage. Non invasive prenatal testing can be done around 10–12 weeks. Another option in the case of unclear genetic test results is fetal muscle biopsy. Treatment
No cure for DMD is known, and an ongoing medical need has been recognized by regulatory authorities. Gene therapy has shown some success.Treatment is generally aimed at controlling symptoms to maximize the quality of life which can be measured using specific questionnaires, and include:

Corticosteroids such as prednisolone and deflazacort lead to short-term improvements in muscle strength and function up to 2 years. Corticosteroids have also been reported to help prolong walking, though the evidence for this is not robust. Randomised control trials have shown that β2 agonists increase muscle strength, but do not modify disease progression. Follow-up time for most RCTs on β2 agonists is only around 12 months, hence results cannot be extrapolated beyond that time frame. Mild, nonjarring physical activity such as swimming is encouraged.