ESPE Abstracts

Achondroplasia is the most common skeletal dysplasia caused by a gain of function of the fibroblast growth factor receptor 3(FGFR3) that impairs endochondral ossification, exiting in short stature and altered bone microarchitecture. Although fractures and reduced bone mineralization are not comorbidities frequently reported, specific normative DXA data are lacking. Aim of the study was to assess bone density parameters in an Achondroplasia cohort. Fifty-seven patients (Female-F=27, Male-M=30) with Achondroplasia were evaluated at the mean age of 11.1±3.8years by DXA(Lunar Prodigy and Lunar iDXA, GE) for bone mineral density(BMD, g/cm2 and Z-score) at the lumbar spine(LS) and total body less head(TBLH). Lumbar bone mineral apparent density(BMAD g/cm3 and Z-score) was calculated based on Crabtree-2017. The delta between LS-BMD Z-score and LS-BMAD Z-score was obtained. Height, weight, body mass index-BMI were recorded and expressed as SDS according to Merker-2018 references. Based on Tanner stage, 35 were prepubertal(61.4%) and 22 post-pubertal(38.6%); 38 patients underwent surgery for foramen magnum stenosis-FMS(66.7%). Overall mean height and BMI were 0.37±0.29 SDS and -0.08±0.31 SDS, respectively. Mean LS-BMD was 0.673±0.030 g/cm2 and -1.41±0.18 Z-score, mean TBLH-BMD was -2.18±0.13 Z-score and mean BMAD 0.247±0.010 g/cm3 and -0.99±0.28 Z-score. M and F differed for BMI-SDS(-0.69±2.85vs0.60±1.38; P=0.04), LS-BMD (0.627±0.140vs0.720±0.24; P=0.09) and LS-BMAD(0.229±0.05vs0.265±0.08; P=0.04), while prepubertal and postpubertal differed for age (P<0.0001), LS-BMD (0.825±0.241vs0.588±0.102; P<0.0001) and LS-BMAD (0.276±0.09vs0.231±0.08; P=0.04). A significant delta between LS-BMD Z-score and LS-BMAD Z-score was found in the postpubertal group(P=0,03). Height-SDS was lower (-0.28±2.63vs-0.775±1.61, P=0.01) and BMI-SDS higher (0.440±1.62vs-1.107±1.62; P=0.0175) in patients that underwent FMS but no differences in DXA bone parameters were found by comparing subjects who underwent or not FMS. In multivariable analyses, TBLH BMD Z-score was predicted by BMI-SDS(coeff 0.188, P=0.01) and FMS (coeff. -0.524, P=0.053) after adjustment for age, gender, pubertal status and FMS (R2 0.152, P=0.02), while LS-BMD Z-score and BMAD Z-score only by BMI-SDS(coeff 0.257, P=0.0008; R2 0.223, P=0.04 and coeff 0.296, P=0.0227; model not significant, respectively). Height-SDS was not a predictor of DXA bone parameters. Preliminary data show that children and adolescent with Achondroplasia display low BMD values for age and sex at the TBLH, low normal values at the LS and normal LSBMAD Z-score values based on references for the general pediatric population; although specific normative data for Achondroplasia are warranted, the use of BMAD is suggested.