GH1 and short stature due to GHSR deficiency: MDK concentrations appeared similar in those children with idiopathic short stature who were receiving growth hormone treatment (n = 11, MDK 0.22 ± 0.03 ng/mL, mean ± SD), as well as in children receiving growth hormone for growth hormone deficiency (n = 4, MDK 0.26 ± 0.06 ng/mL) and children born SGA who failed to catch-up in to the normal range (n = 3, MDK 0.26 ± 0.06 ng/mL), although the small number of subjects in these categories precludes definitive conclusions.