engleski

A 17-month-old boy with bowed legs

Short toddlers with bowed legs usually point to rickets as the probable diagnosis. Enlarged wrists and ankles support the impression and the demonstration of widened and irregular metaphyseal growth plates is consistent with that diagnosis. However, as in our patient, this is not always the case. A reliable history of preventive vitamin D3 intake should arouse suspicion of other forms of rickets such as X-linked hyp”phosphataemia, hypophosphataemia associated with primary or secondary Fanconi syndrome as seen in tyrosinaemia or cystinosis, or the rare "pseudodeficiency" rickets. The finding of normal calcium, phosphate and alkaline phosphatase should then direct the diagnosis towards *group of hereditary skeletal dysplasias, particularly to the metaphyseal dysplasias. Involvement limited to limbs (particularly legs) and to a much smaller extent to ribs, with spared epiphyses and spine, is typical for metaphyseal dysplasias. Normal hair, pancreatic function, immunological tests and absence of other skeletal abnormalities are not suggestive of several types of metaphyseal dysplasias (McKusick, Jansen, Schwachman-Diamond, other associated with immune defects) and make metaphyseal chondrodysplasia, Schmid type the most likely diagnosis. Enlarged femoral capital epiphyses can be seen in this skeletal dysplasia ). Progress in the molecular analysis of skeletal dysplasias allows a relatively easy, non-invasive and accurate diagnosis of many diseases within this group enabling more precise prognosis and genetic counselling. The diagnostic flowsheet of bowed legs and widened growth plates as outlined above suggested a provisional diagnosis of Schmid type metaphyseal chondrodysplasia relatively early and collagen 10 mutation analysis showed a hitherto unreported mutation which is analogous to previously observed ones and thus confirmed the diagnosis. Schmid type metaphyseal chondrodysplasia is inherited as an autosomal dominant trait, but de novo mutations, as in our patient, are not rare. The association between mutations in COLlOA1 (mapped to 6q21-q22.3)and Schmid type metaphyseal chondrodysplasia was first demonstrated by Warman et al. Subsequently, it was found that the great majority of such patients have mutations clustered in the carboxy-terminal region of the gene (5, 7, 8) and that other similar skeletal diseases are not caused by mutations in COLlOA1 8j. The exception was a mutation reccntly reported by Ikegawa et al. associated with metaphyseal dysplasia with spondylar involvement in a single Japanese patient. The expression of collagen 10 is restricted to the hypertrophic zone of the growth plate and this appears to be the explanation for the strictly metaphyseal pattern of Schmid type metaphyseal chondrodysplasia. While most forms of rickets, nutritional or secondary to genetic diseases, are amenable to medical treatment, Schmid type metaphyseal chondrodysplasia is not. Surgical correction of coxa vara and of genua vara is often indicated. Interestingly, during the periods of bed rest associated with medical treatment, the metaphyseal changes can temporarily disappear, indicating that the pathogenesis of the disorder involves mechanical weakness of the growth plates. Complications are unusual and adult height is usually around 140 to 150 cm.

bowed legs; metaphyseal chondrodyspalsia type Schmid; child

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