Non-suppressible insulin-like activity in Laron's syndrome.

Severe growth retardation is found in patients with high levels of growth hormone and low sulphation factor activity or somatomedin. Also non-suppressible insulin-like activity (NSILA-s) has been found to be very low in a patient with this condition as measured by bioassay, protein binding assay and radioimmunoassay and to be below activities found in hypopituitary patients. Partially purified NSILA-s restored the ability of serum to increase sulphation activity although full restitution may still depend on other factors. These findings support the hypothesis that NSILA-s belongs to the family of somatomedin and thus is involved in promoting growth, and that low activity of these growth factors is a primary cause of the growth retardation found in these patients.