ABSTRACT
Genetic counselling in the confusing group of primary bone dysplasias requires special care. The X-linked ‘tarda’ form should be clearly recognisable, even in an isolated case, by the characteristic radiographic appearance of the spine, with a central ‘hump’ of bone and relatively normal distal limb bones. The fact that medication can influence the prognosis by boosting bone mineral content is changing the outlook for those affected. Collagen has always been recognised as fundamental to inherited connective tissue disorders, but it is only recently, with identification of the numerous and often tissue-specific forms of collagen and their genes, that individual diseases can be matched up with particular collagen defects. Marfan syndrome is an important disorder known to be due to deficiency of the connective tissue protein fibrillin, determined by a gene on chromosome 15. The hand deformity superficially resembles severe rheumatoid disease, but the lack of X-ray changes and characteristic pinched face should enable recognition of the syndrome.
