Introduction: Leptin has been postulated as one of the etiologic factors of adolescent idiopathic scoliosis (AIS) because of its functions in regulating bone and energy metabolism. Soluble leptin receptor (sOB-R) has been shown to modulate the bioavailability of leptin. It is hypothesized that AIS girls have different body composition that is associated with abnormal bioavailability of leptin and sOB-R levels.
Materials and methods: 84 AIS girls aged 12 to 14 and 71 age-matched control girls were recruited. Subjects with BMI>23.0 were excluded. Body composition including skeletal muscle mass (SMM) and body fat (BF) mass were measured with bioelectrical impedance analysis. Serum total leptin and sOB-R levels were measured with ELISA.
Results: AIS girls have lower BMI (p=0.008), free leptin index (leptin/sOB-R) (p=0.029) and higher sOB-R (p=0.001) than controls. With multiple regression analysis for the associations between sOB-R vs. percentage BF, BMI and leptin, AIS girls have significantly different slopes (p=<0.001, 0.005 and 0.001 respectively). The subjects were further sub-grouped into normal (18.5<BMI<23.0) and underweight (BMI<18.5) subgroups. After dichotomizing for further analysis, AIS girls with normal BMI have lower percentage SMM (p=0.015), higher percentage BF (p=0.019) and sOB-R level (p=0.001).
Discussion: In AIS girls, sOB-R expression are correlated abnormally with fat content, BMI and leptin compared with controls. It is speculated that AIS girls might have cellular dysfunction resulted in abnormal sOB-R expression, which in turn may cause abnormal leptin bioavailability. With further investigation, sOB-R could potentially develop into a prognostic indicator for predicting the development or progression of AIS.