IS THERE HETEROZYGOTE EXPRESSION OF GROWTH-HORMONE RECEPTOR DEFICIENCY

Expression of heterozygosity for the defect in the growth hormone (GH) receptor has been proposed to be reflected in stature, and in GH bind ing protein (GHBP) and insulin-like growth factor I (IGF-I) levels in parents and other relatives of patients with GH receptor deficiency (G HRD; Laron syndrome). The Ecuadorean population with GHRD, in which he terozygosity can be accurately determined in clinically unaffected rel atives of probands, offers a unique opportunity to consider this issue . It has previously been demonstrated that 17 parents heterozygous for the Ecuadorean mutation of the GH receptor differed little in biochem ical measures (GHBP, IGF-I, IGF-II, IGFBP-2 and IGFBP-3) from Ecuadore an controls. Mean height SDS of 24 non-carrier siblings (-1.3 +/- 0.95 SD) and 41 heterozygote siblings or offspring of probands (-1.8 +/- 1 .15) did not differ significantly (p = 0.08). Thus, although there may be slight heterozygote expression of the defective gene for the GH re ceptor, there is no rationale for counselling based on such minimal va riation.