Metaphysial Dysostosis, Type Schmid.

It is interesting to note the way in which medical knowledge has developed over the years with regard to diseases superficially akin to classical rickets. The first stage followed as a result of the disappearance, owing to the improved knowledge of nutrition, of classical rickets as a common source of bony deformity. This led to the clearer recognition of the remaining 'resistant' forms of rickets, mostly due to renal glomerular disease, to steatorrhoea, or to various hereditary renal tubular dysfunctions. All these resemble classical rickets biochemically, histologically, and radiologically, and heal with very large doses of vitamin D. Now it has become apparent that there remains a further group of diseases that superficially resemble rickets but do not fit into the categories of 'resistant' rickets, since they lack the characteristic biochemical changes, and in particular they show no beneficial response to vitamin D in any dosage. It is tempting to describe examples of this group as having a form of 'chondrodystrophy' or 'developmental defect' and to put them aside as incurable and likely to be unproductive as a source of theoretical knowledge. We prefer to believe, however, that iffurther homogeneous diseases can be defined from this group, and especially if genetic factors can be implicated, then a good case can be made for assuming that there must be a basic biochemical disorder, presumably an inborn error of metabolism. Study of such cases could, therefore, be rewarding if new enzymic functions could be discovered followed by new lines of treatment. We describe here five patients with a disorder closely resembling rickets clinically and radiologically but without the usual biochemical changes and without the usual response to vitamin D.