HUMAN SKIN FIBROBLASTS AS A MODEL OF GROWTH-HORMONE (GH) ACTION IN GHRECEPTOR-POSITIVE LARONS SYNDROME

Congenital GH insensitivity (Laron's syndrome, LS) is often associated with a dysfunctional GH receptor (GHR) causing complete insensitivity to GH and absent serum GH-binding protein (GHBP). However, a proporti on of children with LS have normal GHBP levels. We have identified fou r girls fr om two families with this condition (height so score, -3.4 to -6.8) and undertaken studies on 1) their GHR genes and 2) their GH responses in cultured skin fibroblasts to define the etiology of their GH insensitivities. No GHR gene mutations were identified in one fami ly. In the other family, the affected siblings, an unaffected brother, and the father were heterozygous for a point mutation within exon 6 ( D152H). In addition, use of intron 9 haplotypes to determine linkage t o the GHR gene implied inheritance of different maternal GHR alleles i n the two affected gills of the latter family. It is unlikely, therefo re, that the D152H mutation alone could account for the LS phenotype.E nd points of GH action [DNA synthesis, insulin-like growth factor-bind ing protein-3 (IGFBP-3) messenger RNA (mRNA) and peptide production] i n skin fibroblast cultures established from three of the LS subjects a nd four normal children were examined. Whereas normal Fibroblasts inco rporated [H-3]thymidine dose dependently in response to 10-1000 ng/ml GH (increment at 1000 ng/ml, 77 +/- 19%), LS fibroblasts failed to res pond significantly above basal levels (P < 0.01). In normal fibroblast s, IGFBP-3 mRNA and peptide increased maximally at 48 h in response to 200 ng/ml GH, as determined by ribonuclease protection assay, Western ligand blotting, and RIA. In comparison, LS fibroblasts produced sign ificantly less IGFBP-3 peptide than normal fibroblasts in response to GH, whereas IGFBP-3 mRNA failed to increase above basal levels. These studies have shown that 1) cultured human skin fibroblasts can be used to define the end points of GH action; 2) fibroblast cultures from th e LS children show absent or reduced responses to GH; and 31 GH insens itivity in these children does not appear to be caused exclusively by GHR mutations, but is probably due to dysfunctional GHR signalling. Su ch patients may prove particularly important to elucidation of the key events in GH signaling.