Altered body composition in children and adolescents with achondroplasia.

INTRODUCTION: Achondroplasia is characterized by disproportionate short stature, yet little is known about how growth patterns and body composition differ from peers during childhood and adolescence. We aimed to compare anthropometric variables and detailed body composition profiles between children and adolescents with achondroplasia and age-matched controls. METHODS: In this cross-sectional study, anthropometry and body composition were assessed in participants aged 6-18 years using air displacement plethysmography (BOD POD). Height, weight, BMI, fat mass (FM), fat mass index (FMI), fat-free mass (FFM), and fat-free mass index (FFMI), were compared between individuals with achondroplasia and controls. RESULTS: Participants with achondroplasia showed significantly lower height and weight but higher BMI compared with controls (p < 0.05). FM (kg) was markedly lower in achondroplasia (p < 0.001), whereas FFM (%) and FFMI were significantly higher. In the overall sample and in females, the proportion of FFM was greater in achondroplasia (p < 0.05), whereas differences in males were not significant. Across all age strata, older age groups exhibited higher FM and FFM values, with consistent differences between groups for both components (main effect of group p < 0.01). Age correlated positively with FM and FFM in both groups, but correlations were stronger for FFM (controls: r = 0.75; achondroplasia: r = 0.87; both p < 0.001). DISCUSSION: Children and adolescents with achondroplasia present a distinct body composition profile characterized by lower absolute fat and lean mass but proportionally higher FFM than controls. These findings highlight unique growth and body composition trajectories in achondroplasia and reinforce the importance of condition-specific reference values for nutritional and clinical assessment.