What is the role of genetics in the etiology of hyposomatotropism (growth hormone deficiency [GHD])?

Updated: Jan 24, 2019
  • Author: Sunil Kumar Sinha, MD; Chief Editor: Robert P Hoffman, MD  more...
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Answer

A great deal has been learned about the genetic causes of hypopituitarism. By 1979, many families with isolated GHD or diminished production of GH and one or more additional pituitary hormones had been described. The development of a complementary DNA probe for the pit-hGH gene permitted scientists to recognize GH gene deletions in 1981 and placental GH and chorionic somatotropin gene deletions in 1982. The power of polymerase chain reaction (PCR) amplification and DNA sequencing subsequently revealed mutations and small deletions affecting GH in other families with isolated GHD.

The path to understanding the mechanisms that underlie multiple pituitary hormone deficiency was less straightforward than that regarding single genetic defects. Solutions emerged with the discovery of transcriptional activation factors that direct embryonic development of the anterior pituitary. This story began with the discovery in 1988 of a homeobox protein, called Pit-1, that binds to sequences in the promoter for the GH gene. The story continued with the recognition of many other pituitary and hypothalamic factors that orchestrated pituitary development; 3 main transcriptional factors have been implicated as causes of multiple pituitary hormone deficiency in humans. In chronologic order of their association with human disease, they are Pit-1, PROP1, and HESX1. [19, 20]

The PIT1 gene, located on chromosome 3, is a member of a large family of transcription factor genes responsible for the development and function of somatotrophs and of other neuroendocrine cells of the adenohypophysis. At least 7 point mutations of the PIT1 gene have been associated with hypopituitarism in Dutch, American, Japanese, and Tunisian families.

In 1992, Tatsumi et al described the first human example of pituitary hormone deficiency due to a PIT1 mutation. [26]  Two sisters born to parents who were second cousins had profound neonatal hypothyroidism without elevated levels of thyroid-stimulating hormone. One died from aspiration pneumonia at the age of 2 months. The surviving sister also had deficiencies of GH and prolactin. Multiple recessive and dominant types of PIT1 mutations have been recognized over the years. Sporadic cases have also been reported.

The first examples of PROP1 mutations in humans with pituitary hormone deficiencies were reported in early 1998. In humans, the hormonal phenotype involves deficiencies of luteinizing hormone, follicle-stimulating hormone, prolactin, thyroid-stimulating hormone, and GH. Mutations recognized to date involve the paired-like DNA-binding domain encoded by exons 2 and 3 and demonstrate autosomal recessive inheritance. [20]

The HESX1 gene plays an important role in the development of the optic nerves and the anterior pituitary gland. [27]  The human gene is located on chromosome 3p21.2. Dattani et al identified the first human patients with a mutation in HESX1 after 135 patients with pituitary disorders were screened. [28]


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