Mutation at cleavage site of insulin-like growth factor receptor in a short-stature child born with intrauterine growth retardation

Abstract

Context: Mouse knockout models have clearly demonstrated the critical importance of IGF-I and IGF receptor type 1 (IGF-IR) for embryonic growth as well as postnatal growth. Objective: We hypothesized that mutations of IGF-IR gene might predispose to short stature in children born with intrauterine growth retardation (IUGR). Patients: Twenty-four children with unexplained IUGR (birth weight < -1.5 SD) and short stature (< -2.0 SD) were screened for abnormalities of the IGF-IR gene. Methods: Direct DNA sequencing was used to identify IGF-IR gene mutations. Unprocessed IGF-IR proreceptor in fibroblasts was detected by immunoblot analysis. Functions of mutated IGF-IR in fibroblasts were evaluated by IGF-I binding, and IGF-I-stimulated DNA synthesis and β-subunit autophosphorylation. Results: We found the following results: 1) a heterozygous mutation (R709Q) changing the cleavage site from Arg-Lys-Arg-Arg to Arg-Lys-Gln-Arg was identified in a 6-yr-old Japanese girl (case 1) and her mother who also had IUGR with short stature (case 2); 2) fibroblasts from case 2 contained more IGF-IR proreceptor protein (189 ± 26% of normal) and less mature β-subunit protein (63 ± 12%); 3) [125I]IGF-I binding to fibroblasts from case 2 was reduced, compared with normal control (0.61 ± 0.16 × 106 vs. 1.14 ± 0.12 × 106 sites per cell; P < 0.05); and 4) both IGF-I-stimulated [ 3H]thymidine incorporation and IGF-IR β-subunit autophosphorylation were low in fibroblasts from case 2, compared with those of control (P < 0.05). Conclusions: These findings strongly suggest that this mutation leads to failure of processing of the IGF-IR proreceptor to mature IGF-IR and causes short stature and IUGR. Copyright © 2005 by The Endocrine Society.