Rigamonti AE, et al. - Here, the authors measured the circulating levels of 22 kDa- and 20 kDa-GH in young Prader-Willi syndrome (PWS) patients after combined GH releasing hormone (GHRH)+ arginine (ARG) or ARG administration. Administration of 2 different pharmacological tests (ARG and GHRH + ARG) evoked the same ratios of GH isoforms in PWS. Findings suggested that the hypothalamic dysfunction in this genetic disorder did not alter the qualitative and quantitative composition of GH isoforms present in circulation.