Increased longevity of hypopituitary dwarf mice and GH- resistant knockout mice appears to be in contrast with observations made in clinical practice. In humans, on one hand hypopituitarism and GH deficiency (GHD) are believed to constitute risk factors for cardiovascular disease and, therefore, early death. But on the other hand, patients with a PROP-1 gene mutation, presenting with a combined pituitary-derived hormonal deficiency, can survive to a very advanced age, apparently longer than normal individuals in the same population. The aim of this study was to analyze the impact of untreated GHD on life span. Hereditary dwarfism was recognized in 11 subjects. Genetic analysis revealed an underlying 6.7-kb spanning deletion of genomic DNA encompassing the GH-1 gene causing isolated GHD. These patients (five males and six females) were never treated for their hormonal deficiency and thus provide a unique opportunity to compare their life span and cause of death directly with their unaffected brothers and sisters (11 males and 14 females) as well as with the normal population (100 males and females). Although the cause of death did not vary between the two groups, median life span in the GH-deficient group was significantly shorter than that of unaffected brothers and sisters [males, 56 vs. 75 yr (P < 0.0001); females, 46 vs. 80 yr (P < 0.0001)]. Therefore, with the wealth of information regarding the beneficial effects of GH replacement and the dramatic findings of this study, GH treatment in adult patients suffering from either childhood- or adult-onset GHD is crucially important.

Four distinct familial types of isolated GH deficiency have been described so far, of which type II is the autosomal dominant inherited form. It is mainly caused by mutations within the first 6 bp of intervening sequence 3. However, other splice site and missense mutations have been reported. Based on in vitro experiments and transgenic animal data, there is strong evidence that there is a wide variability in phenotype in terms of the severity of GH deficiency. Therefore, we studied a total of 57 subjects belonging to 19 families suffering from different splice site as well as missense mutations within the GH-1 gene. The subjects presenting with a splice site mutation within the first 2 bp of intervening sequence 3 (5'IVS +1/+2 bp) leading to a skipping of exon 3 were found to be more likely to present in the follow-up with other pituitary hormone deficiencies. In addition, although the patients with missense mutations have previously been reported to be less affected, a number of patients presenting with the P89L missense GH form, showed some pituitary hormone impairment. The development of multiple hormonal deficiencies is not age dependent, and there is a clear variability in onset, severity, and progression, even within the same families. The message of clinical importance from these studies is that the pituitary endocrine status of all such patients should continue to be monitored closely over the years because further hormonal deficiencies may evolve with time.

Human GH has two disulfide bridges linking Cys-53 to Cys-165 and Cys-182 to Cys-189. Although absence of the first disulfide bridge has been shown to affect the bioactivity of GH in transgenic mice, little is known of the importance of this bridge in mediating the GH/GH-receptor (GHR) interaction in humans. However, we have identified a missense mutation (G705C) in the GH1 gene of a Serbian patient. This mutation was found in the homozygous state and leads to the absence of the disulfide bridge Cys-53 to Cys-165. To study the impact of this mutation in vitro, GHR binding and Janus kinase (Jak)2/signal transducer and activator of transcription (Stat)5 activation experiments were performed, in which it was observed that at physiological concentrations (3-50 ng/ml) both GHR binding and Jak2/Stat5 signaling pathway activation were significantly reduced in the mutant GH-C53S, compared with wild-type (wt)-GH. Higher concentrations (400 ng/ml) were required for this mutant to elicit responses similar to wt-GH. These results demonstrate that the absence of the disulfide bridge Cys-53 to Cys-165 affects the binding affinity of GH for the GHR and subsequently the potency of GH to activate the Jak2/Stat5 signaling pathway. In conclusion, we have demonstrated that GH-C53S is a bioinactive GH at the physiological range and that the disulfide bridge Cys-53 to Cys-163 is required for mediating the biological effects of GH.