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Context: G to A transition at position 6,664 (G6664A) in human GH-1 results in the substitution of arginine by histidine at position 183 (R183H) of the GH molecule and causes familial isolated GH deficiency type II (IGHD II)., Objectives: The objective of the study was to assess the phenotype-genotype correlation of subjects affected with IGHD II caused by a G6664A mutation in 34 affected members of two large families., Design and Patients: Sixty-six subjects from two core families were included. The G6664A mutation among family members was determined by restriction fragment length polymorphism., Results: Twenty-four of the 52 members from family 1 and 10 of 14 from family 2 carried the same G6664A mutation in a heterozygous state. The affected subjects in family 1 were significantly shorter [-2.6 vs. -0.1 sd score (SDS), P < 0.0001] and had significantly lower IGF-I serum levels (-1.9 vs. -0.5 SDS, P < 0.0001), compared with normal-genotype family members. The affected adults exhibited great variability in their stature, ranging from -4.5 to -1.0 (mean -2.8 SDS), with five members being of normal height (>-2 SDS). Twelve children were diagnosed with IGHD. Two affected children had normal peak GH levels, although one of these subsequently demonstrated GH insufficiency (6.5 and 3.7 ng/ml). The affected children from both families exhibited large variability in their height, growth velocity, delay in bone age (chronological age - bone age), age at diagnosis, peak GH response, and IGF-I levels., Conclusions: These detailed phenotypic analyses show the variable expressivity of patients bearing a G6664A mutation, reflecting the spectrum of GH deficiency in affected patients, even within families, and the presence of additional genes modifying height determination. Our findings raise a new dilemma in the guidelines for the diagnosis of GH deficiency and the indications for GH therapy.

The growth hormone releasing hormone receptor (GHRHR) plays a critical role in growth. We identified three nominally unrelated kindreds harboring the identical mutation (E72X) in GHRHR, the gene that encodes GHRHR; all three families originated in the Indian subcontinent. Because of the relative geographic proximity of these populations, we employed haplotype analysis in the region of GHRHR to determine the likelihood that this mutation occurred in a common ancestor rather than having occurred on separate occasions in different individuals. Members of all three kindreds segregating the E72X mutation were genotyped for highly polymorphic dinucleotide repeat microsatellites in a 15.5 centimorgan (cM) region around GHRHR on chromosome 7p15. We conclude that the affected individuals share a common ancestor, and we use the association with linked markers to estimate the age of this unique mutation., (Copyright 2003 Wiley-Liss, Inc.)

Objective: G to A transition at position 6664 of the growth hormone (GH-1) gene results in the substitution of Arg183 by His (R183H) in the GH protein and causes a new form of autosomal dominant isolated GH deficiency (IGHD type II). The aim of this study was to assess the bioactivity of this R183H mutant GH in comparison with both other GH variants and the 22-kDa GH in terms of GH-receptor gene regulation., Design and Methods: The regulation of the GH-receptor gene (GH-receptor/GH binding protein, GHR/GHBP) transcription following the addition of variable concentrations (0, 12.5, 25, 50 and 500 ng/ml) of R183H mutant GH was studied in a human hepatoma cell line (HuH7) cultured in a serum-free hormonally defined medium. In addition, identical experiments were performed using either recombinant human GH (22-kDa GH) as a positive control or two GH-receptor antagonists (R77C mutant GH and pegvisomant (B-2036-PEG)) as negative controls. GHR/GHBP mRNA expression was quantitatively assessed by RT-PCR amplification after 0, 1, 3 and 6 h incubation., Results: Following the addition of R183H mutant GH, GHR/GHBP mRNA changed at a similar rate to that seen in experiments where 22-kDa GH was added, indicating equal bioactivity. At all times and concentrations studied, the addition of R77C mutant GH, however, resulted in a significantly lower increase (P<0.001) of GHR/GHBP mRNA concentration compared with that caused by the addition of either 22-kDa GH or R183H mutant GH. Furthermore, in additional experiments, pegvisomant resulted in an absolute block of GHR/GHBP mRNA expression identical to that seen in control experiments where no 22-kDa GH was added at all., Conclusions: These data indicate that the R183H mutant GH, although causing an autosomal dominant form of IGHD has an identical effect on GHR/GHBP transcription as its wild-type, the 22-kDa GH. This implies that the IGHD caused by the R183H heterozygous mutation of the GH-1 gene is mainly due to a block of its regulated GH secretion. In addition, the R77C-GH variant and pegvisomant have an antagonistic effect at the level of GHR/GHBP transcription. All these data were confirmed by run-on experiments. In addition, these data highlight, as far as the GH variants are concerned, that a mutational alteration within the GH-1 gene might cause short stature also on the basis of an altered secretory pathway. This fact has to be taken into consideration when growth retardation is clinically diagnosed and studied at the molecular level. Secretory pathways and, therefore, cell-biological mechanisms are of importance and have to be considered in future not only at the scientific but also at the clinical level.

Familial isolated GH deficiency type II is an autosomal dominant form of short stature, associated in some families with mutations that result in missplicing to produce del32-71-GH, a protein that cannot fold normally. The mechanism by which this mutant suppresses the secretion of wild-type GH encoded by the normal allele is not known. Coexpression of del32-71-GH with wild-type human GH in transient transfections of the neuroendocrine cell lines GH4C1 and AtT20 suppressed accumulation of wild-type GH. The suppression of wild-type GH accumulation by del32-71-GH was a posttranslational effect on wild-type GH caused by decreased stability, rather than decreased synthesis, of wild-type GH. Coexpression of del32-71-GH with human PRL did not suppress accumulation of PRL, indicating that there was not a general suppression of secretory pathway function. Accumulation of del32-71-GH protein was not necessary for the suppression of wild-type GH, because del32-71-GH did not accumulate in the neuroendocrine cell lines in which suppression of accumulation of wild-type GH was observed. Del32-71-GH did accumulate in transfected COS and CHO cells, but did not suppress the accumulation of wild-type GH in these cells. These studies suggest that del32-71-GH may cause GH deficiency in somatotropes of heterozygotes expressing both wild-type and del32-71-GH by decreasing the intracellular stability of wild-type GH.

Since growth hormone deficiency (GHD) causes short stature and metabolic derangements, the processes which control its release are important physiologically. These processes can be illuminated by an understanding of genetically determined GHD. In 2 Indian Moslem cousins from a consanguineous family, GHD resistant to growth hormone releasing hormone (GHRH) stimulation was found. No mutations were found in the growth hormone gene (GH1) (J. Phillips). The receptor for GHRH (GHRHR), implicated in the dwarfism of the little mouse, thus becomes a candidate gene to explain their GHD. Amplification and sequencing a region of GHRHR homologous to that mutated in the little mouse showed a mutation (265G*T) leading to a stop codon at position 72 which would completely prevent GHRHR expression. Subsequently, Maheshwari et al. found an identical mutation in a multiplex kindred from Sindh, Pakistan, about 800 km from the place of origin of our patients. GHD is more commonly caused by recessive or dominant mutations of GH1. The latter are of great interest in understanding the mechanism of GH secretion. In a large kindred with dominant GHD we found a heterozygous 666G*A mutation replacing of Arg with His at amino acid 183. We speculate that the introduced histidine interferes with interactions necessary for correct GH secretion.