Mutations in the NSD1 gene in patients with Sotos syndrome associate with endocrine and paracrine alterations in the IGF system

Objective: To investigate the effect of nuclear receptor Su-var, 3-9, enhancer of zeste, trithorax (SET) domain-containing protein 1 (NSD1) gene alteration in patients with Sotos syndrome on plasma IGFs and IGF-binding proteins (IGFBPs), as well as on the IGF/IGFBP system activity at the tissue level. Design: Twenty-nine patients suspected of Sotos syndrome were divided into two groups: patients with heterozygous deletions or mutations in the NSD1 gene (NSD1(+/-)) (n = 11) and subjects without (NSD1(+/+)) (n = 18). Plasma samples (n = 29) and skin fibroblasts (n = 23) were obtained. The results of both groups were compared and related to reference values. Methods: IGF-I, IGF-II, IGFBP-2, IGFBP-3, lGFBP-4 and lGFBP-6 levels were determined by RIAs. The mitogenic response of fibroblasts to IGFs was investigated by [methyl-(3) H]thymidine incorporation. 1GFBP-3 levels in the culture media were measured by RIA. IGFBP-3 mRNA expression was determined by real time RT-PCR. Results: NSDI+/+ patients showed significantly altered levels of IGF-I (mean - 1.2 SDS), IGF-II (- 1.2), IGFBP-3 (-1.7), IGFBP-4 (-0.4), IGFBP-2 (+0.8) and lGFBP-6 (+1.5). The NSD1(+/+) patients did not differ from the reference, with the exception of the mean IGFBP-3 level (-1.3). Basal proliferation and mitogenic response to IGFs was diminished in NSD1(+/-) fibroblasts compared with NSD1(+/+) (basal, P = 0.02; IGF-I, P < 0.001; IGF-II, P = 0.02). Compared with control fibroblasts, only the mitogenic response was diminished (basal, P = 0.07: IGF-I, P = 0.04; IGF-II, P = 0.04). A trend of higher IGFBP-3 secretion after IGF-I stimulation (P = 0.09) and 3.5-5 times higher mRNA expression of IGFBP-3 in basal conditions was found in NSD1(+/-) fibroblasts in comparison to controls. Conclusions: NSD1(+/-) patients show endocrine and paracrine changes in the IGF system. These changes may contribute to the abnormal growth pattern.