Laron dwarfism and mutations of the growth-hormone receptor gene

Article Abstract:

In Laron dwarfism (LD), a genetic disease, the body does not respond to growth hormone (GH), despite an increase in GH secretion. Because GH interacts with growth hormone receptor (GH-receptor), it is thought that there may be a defect of, or deficiency in, this cell receptor in individuals with LD. To explore the question of whether there could be a defect in the gene that is responsible for GH-receptor, genetic material from individuals with LD and their families was evaluated. The study group included two Mediterranean families in which the parents were blood relatives and some of the children had LD. The results revealed that the genetic trait for LD and genetic abnormalities of LD were always inherited together. Using genetic linkage techniques, a specific DNA mutation was identified in these families. This mutation caused a defect in a protein that is involved in the development of GH-receptor. Seven unrelated individuals with LD were also studied; the mutation found in the families did not occur in these individuals. Further analysis of the genetic material of the seven individuals indicated that different mutations were responsible for these cases of LD. It is suggested that LD can be caused by a genetic mutation that occurs independently in each family, and that this mutation can vary from family to family. More genetic studies of LD families will be necessary to locate other mutation sites responsible for this syndrome. (Consumer Summary produced by Reliance Medical Information, Inc.)

Usage, Diagnosis, Genetic aspects, DNA probes, Chromosome abnormalities, Linkage (Genetics), Somatotropin receptors

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A child-with phenotypic Laron dwarfism and normal somatomedin levels

Article Abstract:

The growth of the body requires a number of hormones, including growth and thyroid hormones, insulin, sex steroids, and somatomedin C. Recently, it has been discovered that there are circulating growth hormone-binding proteins in the blood. One of these proteins appears to be a fragment of the growth hormone receptor, which must bind with the hormone before the cells can cause growth. The exact role of these binding proteins is unknown, but it is suspected that it is important, inasmuch as a particular class of dwarfs (Laron dwarfs, which occur primarily among Sephardic Jews) do not have the protein, and African pygmies have significantly reduced amounts. A four-and-a-half year old boy with severe growth retardation was reported who had no growth hormone-binding proteins in his blood. Unlike a Laron dwarf, he had normal levels of the hormone somatomedin C. Following several examinations of his pituitary function and blood chemistry, it was concluded that either the child was resistant to both growth hormone and somatomedin, or else (and more consistent with other results) it is likely that the growth-hormone binding protein plays an important role in the promotion of growth. This case represents an extreme example of the unclear association between known growth hormone-binding protein and body growth.

Research, Case studies, Carrier proteins, Transport proteins, Growth disorders, column

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Low levels of high-affinity growth hormone-binding protein in African Pygmies

Article Abstract:

It is not known why African Pygmies are short in stature and why their bodies do not respond to growth hormone. Low levels of an insulin-like substance needed by the receptors that growth hormone triggers suggest that the reason is a defficiency of growth-hormone receptors. The high-affinity growth hormone binding protein is a part of the growth hormone receptor, and levels of it may indicate the number of these receptors in body tissues. Pygmies have half as much of this protein as do non-Pygmy blacks or whites, though values for Pygmies and non-Pygmies overlap widely. Pygmies have levels of low-affinity binding protein similar to those of non-Pygmies. Thus Pygmies have fewer growth hormone receptors that do non-Pygmies, though there may be additional unrelated reasons for their short stature.

Physiological aspects, Blood chemical analysis, Pygmies, blood

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