Molecular and cellular basis of isolated dominant-negative growth hormone deficiency, IGHD type II: insights on the secretory pathway of peptide hormones

Estimates of the frequency of GH deficiency range from 1:4,000 to 1:10,000. Most cases are sporadic and presumed to be secondary to a wide variety of aetiologies. However, in families with consanguinity, or when a second case occurs in the same family, a genetic cause may be suspected. Given that the patient is isolated GH deficient four distinct familial types of isolated GH deficiencies (IGHD) are well-differentiated on the basis of inheritance, hormonal deficiencies as well as molecular analyses. Two forms are autosomal recessively (IGHD type IA and IB), one is autosomal dominantly (IGHD type II) and one X-linked inherited. In this review, we focus on the secretory pathway of peptide hormones in general and on the possible mechanisms causing IGHD type II in detail. Most interestingly, in IGHD type II the apparently same phenotype of IGHD is caused by distinct GH-1 gene alterations leading to different blockades within the secretory pathway. Furthermore, this type of IGHD, in addition to some other specific GH-1 gene mutations, provides the most important opportunity to shed light on cell-biological mechanisms far beyond its pure description at the DNA/RNA level.