Reduced exercise capacity in untreated adults with primary growth hormone resistance (Laron syndrome)

OBJECTIVE: Primary IGF-I deficiency (Laron syndrome, LS) may decrease exercise capacity as a result of a lack of an IGF-I effect on heart, peripheral muscle or lung structure and/or function. METHODS: Eight patients (six females) who had never received treatment with IGF-I, with mean age of 36 ± 10 (SD) years (range 21-48), weight 47 ± 9 kg (31-61), height 126 ± 12 cm (112-140) and body mass index of 29 ± 4 kg/m² (24-34), and 12 age-matched controls, underwent lung function tests and incremental cycling to the limit of tolerance (CPX, MedGraphics). Predicted values for the patients were derived from adult equations based on height. RESULTS: In LS patients, lung function was near normal; vital capacity was 84 ± 11% of expected (66-103). Peak exercise O₂-uptake and the anaerobic threshold were reduced, 57 ± 20% of predicted and 33 ± 9% of predicted peak (P = 0.005 vs. controls), despite normal mean exercise breathing reserve. All parameters were normal In the controls. CONCLUSION: Exercise capacity in untreated adults with LS is significantly reduced.The limitation for most patients was not ventilatory but resulted either from low cardiac output and/or from dysfunction of the peripheral muscles. However, the relative contribution of each of these elements and/or the role of poor fitness needs further study.