Spermine deficiency in Gy mice caused by deletion of the spermine synthase gene.

Two mouse mutations gyro (Gy) and hypophosphatemia (Hyp) are mouse models for X-linked hypophosphatemic rickets and have been shown to be deleted for the 5' and 3' end of the mouse homolog of PHEX (phosphate regulating gene with homologies to endopeptidases on the X chromosome; formerly called PEX), respectively. In addition to the metabolic disorder observed in Hyp mice, male Gy mice are sterile and show circling behavior and reduced viability. The human SMS (spermine synthase) gene maps approximately 39 kb upstream of PHEX and is transcribed in the same direction. To elucidate the complex phenotype of Gy mice, we characterized the genomic region upstream of Phex. By establishing the genomic structure of mouse Sms, a 160-190 kb deletion was shown in Gy mice, which includes both Phex and Sms. There are several pseudogenes of SMS / Sms in man and mouse. Northern analysis revealed three different Sms transcripts which are absent in Gy mice. Measurement of polyamine levels revealed a marked decrease in spermine in liver and pancreas of affected male Gy mice. Analysis of brain tissue revealed no gross or histological abnormalities. Gy provides a mouse model for a defect in the polyamine pathway, which is known to play a key role in cell proliferation.

Pex gene deletions in Gy and Hyp mice provide mouse models for X-linked hypophosphatemia.

X-linked hypophosphatemic rickets in humans is caused by mutations in the PEX gene which codes for a protein homologous to neutral endopeptidases. Hyp and Gy mice both have X-linked hypophosphatemic rickets, although genetic data and the different phenotypic spectra observed have previously suggested that two different genes are mutated. In addition to the metabolic disorder observed in Hyp mice, male Gy mice are sterile and show circling behavior and reduced viability. We now report the cloning of the mouse homolog of PEX which is highly conserved between man and mouse. The 3' end of this gene is deleted in Hyp mice. In Gy mice, the first three exons and the promotor region are deleted. Thus, Hyp and Gy are allelic mutations and both provide mouse models for X-linked hypophosphatemia.

Three novel mutations of the NF1 gene detected by temperature gradient gel electrophoresis of exons 5 and 8.

We screened a total of 100 unrelated patients with neurofibromatosis type 1 (NF1) for mutations on exons 5 and 8 of the NF1 gene using temperature gradient gel electrophoresis (TGGE). Careful interpretation of exon 5 TGGE patterns was necessary due to interference by an exonic polymorphism. Three novel mutations were identified: a stop mutation in exon 5 (Q239X) caused by a C-->T transition at cDNA nucleotide position 715, a transition at the invariant G of the splice acceptor site in the intron 4c (G655-1A), and a transversion at the invariant G of the splice donor site in intron 8 (G1185 + 1T). Analysis of mRNA revealed the predicted abnormal splice products. While skipping of exon 5 causes a shift in the reading frame with a premature stop codon downstream in the middle of exon 6, skipping of exon 8 leads to an in-frame deletion with the predicted protein product being shortened by 41 amino acids.

Reduced neurofibromin content but normal GAP activity in a patient with neurofibromatosis type 1 caused by a five base pair duplication in exon 12b of the NF1 gene.

We screened a total of 87 unrelated patients with neurofibromatosis type 1 (NF1) for mutations in exons 11, 12a, and 12b of the NF1 gene using temperature gradient gel electrophoresis (TGGE). A novel mutation (1998insCCTCT) was found in exon 12b. The 5-bp duplication comprising nucleotides 1994 to 1998 is predicted to lead to a truncated protein product lacking three quarters of its C-terminal sequence including the entire GTPase-activating protein-(GAP)-related domain. This mutation is associated with a reduction by 50% of the detectable amount of neurofibromin found in this patient. Despite the reduced level of neurofibromin cellular GAP activity was normal, which suggests that defects in other functions of the neurofibromin molecule may be important in the pathogenesis of NF1.

Two recurrent nonsense mutations and a 4 bp deletion in a quasi-symmetric element in exon 37 of the NF1 gene.

We screened a total of 92 unrelated patients with neurofibromatosis type 1 (NF1) for mutations in exon 37 of the NF1 gene, by using temperature gradient gel electrophoresis. Two novel mutations were found: a 4 bp deletion in a so-called quasi-symmetric element (6789del-TTAC) and a recurrent nonsense mutation, which was identified in two unrelated patients, at codon 2264 (C6792A). The independent origin of the latter mutation in two families was confirmed by haplotype analysis. The nonsense mutation and the 4 bp deletion are both predicted to lead to a truncated protein product lacking the C-terminal 20% (approximately) of its sequence. The occurrence of three independent mutations among 92 NF1 patients at codons 2263-2264 (exon 37) suggests that a specific search for mutations in this area should be undertaken in screening programs for NF1 mutations.