Severe rhizomelic shortening in a child with a complex duplication/deletion rearrangement of chromosome X.

Mesomelic and rhizo-mesomelic dysplasias are a group of disorders characterized by abnormal shortening of the limbs. One of the most common causes of mesomelic shortening is the loss of the transcription factor SHOX. In this clinical report, we present a patient who in addition to mesomelic shortening has severe rhizomelic shortening and developmental delay. Karyotyping revealed a recombinant X chromosome in which the region distal to Xp22.33 (where SHOX is found) was replaced with material from Xq28. Included in the region distal to Xq28 is the gene MECP2 and this patient presents with features of MECP2 duplication syndrome. We find that this patient has skeletal features not typical with the loss of SHOX that are likely explained by the rearrangement of the X chromosome. Further delineation of this rearrangement may allow for the identification of additional genetic mechanisms critical for the development of the limbs.