Complete SHOX deficiency causes Langer mesomelic dysplasia

The SHOX (short-stature homeobox-containing) gene encodes isoforms of a homeo-domain transcription factor important in human limb development. SHOX haploin-sufficiency has been implicated in three human growth disorders: Turner syndrome, idiopathic short stature, and Leri-Weill dyschondrosteosis. Langer mesomelic dysplasia is thought to be the homozygous form of dyschondrosteosis. However, complete SHOX deficiency has not been demonstrated for any postnatal patient with the classic Langer phenotype. We studied four adults and one child with Langer mesomelic dysplasia. SHOX abnormalities were detected in all five probands. One was a homozygote or hemizygote and two were compound heterozygotes. The homozygous or hemizygous mutation was in exon 6a, implying that the SHOXa isoform is essential for normal skeletal development. These findings confirm clinical inferences that Langer mesomelic dysplasia is the homozygous form of Leri-Weill dyschondrosteosis and add to our understanding of genotype/phenotype relationships in SHOX deficiency disorders.