ESPE Abstracts

Background: Various aspects of IGF1R defects have been analysed to date, but the effects of IGF1R haploinsufficiency bone status and metabolism were rarely investigated.

Objective and hypotheses: To study bone metabolism and structure in a case of Insulin-like growth factor-I (IGF-I) receptor (IGF1R) gene deletion.

Method: Genetic analysis, GH stimulation, rhGH treatment, CGH-array, dual-X-ray absorptiometry (DXA), peripheral quantitative computed tomography (pQCT), phalangeal bone sonography, bone metabolism study were carried out in this patient.

Results: We report a patient referred to our centre at the age of 18 months for failure to thrive. GH stimulation tests revealed a GH deficiency (GH peak after arginine 8.92 ng/ml, after clonidine 6.92 ng/ml), whereas IGF-I was 248 ng/ml. rhGH treatment (0.23 mg/kg per week) showed only a slight improvement (from −5.1 to −3.5 SDS). Target height was 166.5 cm (0.67 S.D.). So, at 10 years of age, the child was re-evaluated: CGH-array identified a heterozygous de novo 4.92 Mb deletion in 15q26.2, including the IGF1R gene. DXA showed a normal BMD z-score (the BMD z-score corrected for height was 0.6), while pQCT revealed very reduced cortical (−6.9 SDS) and increased trabecular density (3.8 SDS). The total density was normal (0.7 SDS), whereas we showed a significantly reduced bone area for muscle area (−4.0 SDS) and for height (−4.1 SDS). The SSI polar (−2.2 SDS) was significantly reduced. Fat area was also poorly represented (−1.8 SDS). Phalangeal bone sonography showed significantly reduced AD SoS and BTT values. Bone metabolism study revealed a reduced bone modelling and accrual with moderately high PTH and reduced osteocalcin, bone alkaline phosphatase and urinary deoxypyridinoline concentrations.

Conclusion: Our study showed the presence of changes in bone architecture, quality, and metabolism in heterozygous IGF1R deletion patients, supporting IGF-I as key in bone modelling and accrual.