Growth without growth hormone: evidence for a potent circulating human growth factor.

A potent growth factor was detected in the serum of a child with growth hormone (GH) deficiency and early growth delay whose growth velocity spontaneously increased to supranormal levels despite persistent GH deficiency by both radioimmunoassay (RIA) and radioreceptor assay. Thyroid function, prolactin, insulin response to oral glucose, glucose response to intravenous insulin, and computerised tomography of the head were all normal. Whilst somatomedin-C levels measured by RIA were low or low-normal, in vitro somatomedin bioactivity measured by bioassay was normal, suggesting the presence of a growth factor other than somatomedin-C. By way of confirmation, the patient's serum was incubated with erythroid progenitor cells from peripheral blood of a normal individual and a Laron dwarf. In this system, proliferation of normal erythroid progenitors was almost double that obtained with physiological concentrations of GH or control sera, and Laron erythroid progenitors, which were completely resistant to added GH, also responded strongly to the patient's serum. The patient's growth is therefore independent of GH and other known growth factors.