[Obesity characteristics and body composition in children with osteogenesis imperfecta]

Objective: To describe the clinical symptoms, obesity status and body composition distribution in children with osteogenesis imperfecta (OI). Methods: This retrospective cohort study included 45 children aged 0-18 years with OI, diagnosed by clinical and genetic testing at Children's Hospital, Zhejiang University School of Medicine, from October 2020 to February 2025. Clinical data were collected on age, sex, symptoms, imaging examinations and genetic testing results. According to body mass index (BMI) criteria or weight-for-length Z-score, the OI patients were divided into non-overweight or obese group and overweight or obese group. Concurrently, 60 children with simple overweight or obesity, matched for sex, age and BMI, were enrolled as a control group. The t-test and Mann-Whitney U test were used to compare the clinical characteristics between the 2 OI groups, and body composition (lean mass index (LMI)and fat mass index (FMI)) between the overweight or obese OI group and the control group. Fracture frequency distribution between the two OI groups were compared using the χ² test. Results: Of the 45 OI children, 26 were male and 19 female, with an average age of (7.2±3.9) years. Genetic variants involved COL1A1 or COL1A2 in 40 cases, IFITM5 in 3, SERPINF1 in 1, and BMP1 in 1. Of the OI patients, 18 (40%) were in the overweight or obesity group and 27 (60%) in the non-overweight or obesity group; 19 (42%) had short stature or growth retardation. Between the 2 OI groups, none of sex, osteocalcin, bone mineral density Z-score, or vitamin D level differed significantly (all P>0.05), whereas fracture frequency did differ significantly (P<0.05). Twenty seven OI children (13 in the overweight or obesity group and 14 in the non-overweight or obesity group) completed the dual-energy X-ray absorptiometry, and all of them had COL1A1 or COL1A2 genotypes. The FMI level was higher in the overweight or obese group than in the non-overweight or obese group (9.0 (6.1, 9.6) vs. 4.4 (3.7, 5.6) kg/m², Z=3.21, P=0.005), whereas LMI and abdominal-to-gluteal fat percentage ratio did not differ significantly (both P>0.05). In the OI overweight or obesity group, both FMI and LMI were lower than in the control group (9.0 (6.1, 9.6) vs. 10.4 (9.2, 11.7) kg/m², 12.1 (11.7, 12.9) vs. 13.9 (13.0, 15.1) kg/m², Z=3.45,3.72, both P<0.05). Conclusions: Overweight or obesity was prevalent among children with OI and was closely associated with fracture frequency. Among those with COL1A1 or COL1A2 variants, the overweight or obese OI children was characterized by higher FMI and lower LMI.