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Tricho-dento-osseous dysplasia (TDO) belongs to the ectodermal dysplasias and is characterised by curly/kinky hair at birth, enamel hypoplasia with discolouration and molar taurodontism, increased overall bone mineral density (BMD) and increased thickness of the cortical bones of the skull. The prevalence is unknown but the disease has been described in at least 8 families with over 30 affected members in some large kindreds. The disease shows significant inter and intrafamilial clinical variation, with enamel hypoplasia and taurodontism being the most consistent features, however, the extent of the enamel defects may also vary between affected family members. The hair and bone manifestations are more variable and age dependent. Curly/kinky hair is present at birth in around 80% of patients, but around half of these patients loose the hair phenotype by adolescence. The BMD measurements show increasing variability with age, particularly in the radius and ulna. In addition, spinal BMD shows an increase with age. Other reported features include flat/brittle fingernails, increased susceptibility for caries and abscesses, delayed dental eruption, tubular sclerosis of the long bones, dolichocephaly (as a result of craniosynostosis), and an absence of mastoid pneumatisation, the frontal sinus and calvarial diploe. The disease is transmitted as a highly penetrant autosomal dominant trait and is caused by mutations in the distal-less homeobox gene (DLX3), located on the long arm of chromosome 17 (17q21.3-q22). Diagnosis can be made by clinical and radiological examination and confirmed by detection of DLX3 mutations. The differential diagnosis should include amelogenesis imperfecta, hypomaturation-hypoplastic type, with taurodontism (AIHHT), oculodentoosseous dysplasia (see this term) and the autosomal dominant form of osteopetrosis (see this term). Treatment is symptomatic and patients require frequent dental follow-up. The prognosis is good and there appears to be no predisposition for developing fractures. |