Unexpected phenotype in a boy with trisomy of the SHOX gene.

The assessment that heterozygous SHOX mutations leading to SHOX haploinsufficiency play a role in patients with idiopathic short stature (ISS) is already documented in the literature as well as the suggestion that additional copies of SHOX are strongly implicated in a condition of tall stature. However, we report the first case of short stature in a male associated with the presence of three copies of the SHOX gene. Through chromosomal analysis, using Multiplex Ligation-dependent Probe Amplification method of SHOX salsa P018B kit and microsatellite analysis, we identify a new interstitial isolated duplication of the SHOX gene and its enhancer caused by a larger duplication of the PAR1 region in a boy with ISS. Consequently, we propose the hypothesis that this chromosome re-arrangement disrupts the regular interaction between the enhancer and promoter, resulting in a transcription block, thus producing a lack of gene activation, causing the clinical feature of short stature.