Bone geometry and volumetric bone density at the radius in patients with isolated SHOX deficiency

The short stature homeobox-containing gene (SHOX) plays an important role in bone development and growth. We aimed to assess bone geometry and volumetric bone mineral density at the radius in patients with isolated SHOX deficiency and to relate these bone parameters to the severity of disproportion between the upper and the lower body segment. 17 patients with isolated SHOX deficiency (median age 12.3 yrs, range 6.7-37.2, 12 children and 5 adults) were examined by peripheral quantitative CT (pQCT) at the non-dominant forearm. Results were expressed as Z-scores using published reference data. Linear regression analyses were performed to describe associations between pQCT parameters and the severity of disproportion expressed as sitting height to standing subischial leg height ratio. Trabecular volumetric bone mineral density (vBMD) at the distal radius was normal, whereas cortical vBMD was decreased (mean Z-scores 0.34±1.5, n.s., and -2.2±2.2, p<0.001, respectively). Total bone cross-sectional area was enlarged at the diaphysis (2.1±1.2, p<0.001), while cortical bone cross-sectional area was normal (-0.51±1.4, n.s.). Consequently, cortical thickness was decreased (-1.2±1.3, p<0.01). The polar strength-strain index as a surrogate of long bone strength was normal (0.40±1.4, n.s.). We found no associations between pQCT parameters and the severity of disproportion.

Patients with isolated SHOX deficiency are characterized by decreased cortical vBMD and cortical thickness and enlarged diaphysis. As similar changes have been described in girls with Turner syndrome, these findings suggest that haploinsufficiency of SHOX could cause characteristic skeletal anomalies at the radius.