THE INSULIN-LIKE GROWTH-FACTOR-I GENERATION TEST IN THE INVESTIGATIONOF SHORT STATURE

Genotypic and phenotypic heterogeneity in patients with growth hormone (GH) insensitivity syndrome suggests that partial defects exist in th e GH receptor. The insulin-like growth factor I (IGF-I) generation tes t was assessed as a means of identifying partial GH receptor defects i n a heterogeneous group of 22 prepubertal children with short stature. In a subgroup of nine patients with peak GH levels of 63.7 +/- 3.7 mU /l during a glucagon tolerance test, the response to the IGF-I generat ion test was no different from that for the group as a whole (peak GH, 43.3 +/- 4.5 mU/l), despite the fact that this subgroup exhibited a n egative relationship between height SDS and peak GH and a positive rel ationship between height SDS and IGF binding protein-3. This prelimina ry study therefore suggests that the IGF-I generation test in its pres ent form will not be useful as a primary screening test for partial GH insensitivity. Despite this, the IGF-I generation test has been extre mely useful in the confirmation of the diagnosis of GHIS and may there fore also prove useful in the confirmation of partial defects in the G H receptor. A subgroup of short children with peak GH levels above 40 mU/l had some characteristics of partial GH receptor deficiency. These children, to whom GH therapy would not normally be given, may respond better to recombinant human IGF-I.