Laron syndrome

Laron syndrome, or Laron-type dwarfism, is an autosomal recessive disorder characterized by an insensitivity to growth hormone (GH), caused by a variant of the growth hormone receptor. It causes short stature and a resistance to diabetes and cancer.

Eponym
It is named after Zvi Laron, the Israeli researcher who, with A. Pertzelan and S. Mannheimer, first reported the condition in 1966, based upon observations which began in 1958.

Resistance to GH was first reported by Laron in 1966. Since then, severe resistance to GH, characterized by grossly impaired growth despite normal levels of GH in serum, has been termed Laron syndrome.

Pathophysiology


Molecular genetic investigations have shown that this disorder is mainly associated with mutations in the gene for the GH receptor. These can result in defective hormone binding to the ectodomain or reduced efficiency of dimerization of the receptor after hormone occupancy. There are exceptionally low levels of insulin-like growth factor (IGF-1) and its principal carrier protein, insulin-like growth factor binding protein 3.

A related condition involving postreceptor insensitivity to growth hormone has been associated with STAT5B.

Clinical characteristics
The principal feature of Laron syndrome is abnormally short stature (dwarfism). Physical symptoms include: prominent forehead, depressed nasal bridge, under-development of mandible, truncal obesity and a very small penis. Seizures are frequently secondary to hypoglycemia. Some genetic variations have an impact upon intellectual capacity.

The majority of reported cases have been of Arabic or Semitic origin, with numerous patients in Israel, Saudi Arabia, Egypt, Iraq, and remote villages in Ecuador with Sephardic roots.

In 2011, it was reported that people with this syndrome in the Ecuadorian villages are resistant to cancer and diabetes and are somewhat protected against aging. This is consistent with findings in mice with a defective growth hormone receptor gene.

Treatment
Administration of GH has no effect on IGF-1 production, therefore treatment is mainly by biosynthetic IGF-1. IGF-1 must be taken before puberty to be effective.

IPLEX (Mecasermin rinfabate) is composed of recombinant human IGF-1 (rhIGF-1) and its binding protein IGFBP-3. It was FDA approved in 2005 for treatment of primary IGF-1 deficiency or GH gene deletion. Side effects from IPLEX are hypoglycemia.

Prognosis
People with Laron syndrome have strikingly low rates of cancer and diabetes.

Homo floresiensis
Recent publications have proposed that Homo floresiensis represented a population with widespread Laron syndrome. This hypothesis has received criticism and is unconfirmed.