GENETIC AND MOLECULAR ANALYSIS OF FAMILIAL ISOLATED GROWTH-HORMONE DEFICIENCY

Familial isolated growth hormone deficiency (IGHD) has been associated with complete deletions of the hGH-N gene encoding the pituitary grow th hormone (GH) in a large number of cases. However, there is still no alternative empirical explanation for the remaining familial or non-f amilial IGHD cases. We studied a large kindred including five IGHD-aff ected first cousins to determine possible IGHD inheritance and whether the hGH-N gene was the cause of IGHD in this pedigree. Sex-linked and autosomal recessive transmission of IGHD in this kindred was rejected . Autosomal dominant inheritance was the most probable explanation acc ording to a model of one locus with two alleles, one being dominant fo r IGHD, under genetic modifiers or epistasis. Southern blotting analys is (BamHI and HindIII digestions) was used to determine whether the hG H-N gene was present in the patients and their family members. Because we found that the hGH-N gene was present, five restriction fragment l ength polymorphisms (RFLPs; HincII, MspI-A and B, and BglII-A and B) l inked to the hGH-N gene were used to try, to identify the possible RFL P haplotypes in the pedigree that could be markers or associated with the abnormal hGH-N alleles responsible for IGHD. From the haplotype an alysis, it appeared that other genes not linked to the hGH-N gene clus ter were the cause of the IGHD phenotype in this kindred. An alternati ve conclusion could be that the hGH-N gene was responsible for IGHD in this kindred, if a mutation (gene conversion) at the MspI-B site or a reciprocal recombination event between the HincII and MspI-B sites oc curred from generation P to F1 and a similar event took place from gen eration F1 to F2. The non-significant GH responses of patients to the growth releasing factor test confirmed that the hGH-N gene structural product or some step in its regulation was responsible for causing IGH D in this kindred. We suggest that genetic micromutations in the hGH-N gene are present and are responsible for IGHD. We developed a method using the polymerase chain reaction to amplify a 790-bp fragment of th e hGH-N gene. The fragment spanned from the second part of the dyad sy mmetry region in the non-transcribed 5' end of the hGH-N gene to 9 bp before the alternative splice-acceptor site in exon 3. The expected fr agment was verified by its digestion with seven diagnostic resctrictio n endonucleases (BamHI, FspI, PstI, NdeI, BssHII, BglII and HincII). T he results showed no deletions or insertions greater than 35 bp in the hGH-N amplified fragment from the DNAs of the IGHD patients and their family members.