No abstract

At least three different sizes of GH-1 gene deletions (approximately 6.7, 7.0 and 7.6 kilobases) have been detected by Southern blot analysis of DNA from individuals with familial isolated GH deficiency type IA (IGHD1A). It is likely that these deletions result from unequal crossing over events between homologous regions that flank the GH-1 gene. Heterogeneity in clinical phenotypes is suggested by reports of good responses to exogenous GH treatment in most IGHD1A subjects with 7.6 kilobase deletions as opposed to poor responses in many subjects with smaller deletions. To determine if characteristic differences in gene deletions could be detected that correlate with response to treatment we analyzed the DNA sequences that normally flank the GH-1 gene. Digestion patterns of the PCR amplification products of these sequences from DNA of IGHD type IA patients with the restriction endonucleases BglI, HaeII, or SmaI showed characteristic differences for each of the three deletion sizes studied. The location and size of all deletions agreed with previous size estimates based on Southern blot analysis. Interestingly, clinical differences observed in the development of high titers of anti-GH antibodies and poor growth responses after GH treatment are unexplained, since discordant outcomes were observed in patients who had deletions of the same size and approximate location.

Abstract. We carried out screening for mutations in the GH-1 gene in 29 sporadic Japanese subjects with severe Isolated Growth Hormone Deficiency (IGHD) by dideoxy fingerprinting (ddF). Three of 29 (N 10%) were heterozygous for each of the following GH-1 gene mutations including: 1) an G--'A transition in the third codon of the GH-1 signal peptide of exon 1 resulting in a Threonine to Alanine substitution, 2) a G--~A transition in the first base of the donor splice site of IVS 3 (+1G--A) and 3) a G-' A transition in the 183rd codon of the GH-1 mature peptide of exon 5 resulting in an Arginine to Histidine substitution.One of three was heterozygous for both mutations of 1) and 2). The IVS 3 (+1G-~A) mutation has been previously reported in affected individuals from three unrelated families with IGHD type II (autosomal dominant form). This mutation destroys the GH IVS 3 donor splice site, causing skipping of exon 3 and loss of the codons for amino acids 32-71 of the mature GH peptide. Our findings indicate that 1) ddF screening of genomic DNAs provides a practical tool to detect GH gene mutations and 2) some sporadic cases of IGHD may be caused by GH gene alternations.

MutE has not been previously reported and is the fourth mutation associated with IGHD type II. The guanine residue mutated in mutA was the second nucleotide of a CpG dinucleotide, which is regarded as a hot spot for mutations by a methylation-deamination mechanism. Since mutA has previously been identified in three type II IGHD kindreds belonging to different ethnic backgrounds, this appears to be the most frequent GH-I gene mutation in IGHD with a dominant inheritance. Because de novo mutations appeared to have occurred in all three families analyzed in the present study and the presence or absence of these mutations can easily be tested by PCR and restriction enzyme digestion, not only the familial cases but also sporadic cases with IGHD should be examined for a possible mutation at the donor splice site of intron 3 in the GH-1 gene.