Background: Prader-Willi Syndrome (PWS) is a complex genetic disorder characterised by developmental and growth abnormalities, insatiable appetite, and excessive eating (hyperphagia). Hyperphagia is thought to be driven by supraphysiological levels of the appetite hormone ghrelin. The underlying causes of hyperghrelinaemia in PWS are currently unknown, however. Recently, ghrelin-reactive autoantibodies (isotype IgG) were identified in non-genetic obesity and were found to reversibly bind circulating ghrelin and, acting as carrier proteins, protect ghrelin from degradation, thereby potentiating its appetite-stimulating effects.
Objectives: This project aimed to measure ghrelin-reactive autoantibodies in children with PWS. We hypothesised that patients possess higher levels of ghrelin-reactive autoantibodies compared to their unaffected sibling controls. We also tested whether the inactive ghrelin isoform, unacylated ghrelin (UAG), outcompetes ghrelin and sequesters autoantibodies ex vivo.
Methods: Blood samples were taken from patients and matched sibling controls after an overnight fast and 10, 20, 30, 60 and 120 minutes after a standardised mixed meal. Plasma was extracted and ghrelin-reactive autoantibodies were measured using ELISA. To test specificity of the ELISA and to determine if the autoantibodies bind to UAG, the samples were also pre-absorbed with exogenous ghrelin and UAG (10-6 M) prior to being subjected to separate ELISAs.
Results: We have demonstrated that children with PWS have significantly higher levels of plasma ghrelin-reactive autoantibodies compared to controls after an overnight fast (P<0.0001, unpaired t test). Food intake did not affect autoantibody levels in patients or controls. Both ghrelin and UAG pre-absorbed controls showed significant reduction of ghrelin-reactive autoantibody detection in the PWS and control groups (P<0.001, unpaired t test), suggesting that the autoantibodies complex with both isoforms.
Conclusions: Increased levels of ghrelin-reactive autoantibodies in children with PWS may contribute to the hyperghrelinaemia and hyperphagia that characterises PWS. Targeting these autoantibodies may be a future therapeutic avenue for this incurable condition.