Intrafamilial phenotypic variability in Engelmann disease (ED): are ED and Ribbing disease the same entity?

We report on clinical and radiologic manifestations in a 3-generation Japanese family with Engelmann disease (ED) or progressive diaphyseal dysplasia. A large variation of phenotype was remarkable among 12 affected family members. Of the 12 patients, 7 had full manifestations of ED, such as bilateral, symmetrical diaphyseal sclerosis of long bones with myopathy and limb pain, whereas the other 5 exhibited only segmental (rhizomelic and/or mesomelic) involvement and asymmetric diaphyseal sclerosis without any clinical symptoms. The phenotype of the latter group of patients resembled Ribbing disease (RD). We propose that ED and RD represent phenotypic variation of the same disorder.