X-linked hypophosphatemic rickets (HYP) is a dominant disorder characterised by impaired phosphate uptake in the kidney, which is likely to be caused by abnormal regulation of sodium phosphate cotransport in the proximal tubules. By positional cloning, we have isolated a candidate gene from the HYP region in Xp22.1. This gene exhibits homology to a family of endopeptidase genes, members of which are involved in the degradation or activation of a variety of peptide hormones. This gene (which we have called PEX) is composed of multiple exons which span at least five cosmids. Intragenic non-overlapping deletions from four different families and three mutations (two splice sites and one frameshift) have been detected in HYP patients, which suggest that the PEX gene is involved in the HYP disorder.

Ellis-van Creveld syndrome (EvC, MIM 225500) is an autosomal recessive skeletal dysplasia characterized by short limbs, short ribs, postaxial polydactyly and dysplastic nails and teeth. Congenital cardiac defects, most commonly a defect of primary atrial septation producing a common atrium, occur in 60% of affected individuals. The disease was mapped to chromosome 4p16 in nine Amish subpedigrees and single pedigrees from Mexico, Ecuador and Brazil. Weyers acrodental dysostosis (MIM 193530), an autosomal dominant disorder with a similar but milder phenotype, has been mapped in a single pedigree to an area including the EvC critical region. We have identified a new gene (EVC), encoding a 992-amino-acid protein, that is mutated in individuals with EvC. We identified a splice-donor change in an Amish pedigree and six truncating mutations and a single amino acid deletion in seven pedigrees. The heterozygous carriers of these mutations did not manifest features of EvC. We found two heterozygous missense mutations associated with a phenotype, one in a man with Weyers acrodental dysostosis and another in a father and his daughter, who both have the heart defect characteristic of EvC and polydactyly, but not short stature. We suggest that EvC and Weyers acrodental dysostosis are allelic conditions.

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.

X-linked dominant hypophosphatemic rickets (HYP) is the most common form of hereditary rickets. Recently we have cloned the PEX gene and shown it to be mutated and deleted in HYP individuals. We have now completely sequenced a 243-kb genomic region containing PEX and have identified all intron-exon boundary sequences. We show that PEX, homologous to members of a neutral endopeptidase family, has an exon organization that is very similar to neprilysin. We have performed an extensive mutation analysis examining all 22 PEX coding exons in 29 familial and 14 sporadic cases of hypophosphatemia. Sequence changes include missense, frameshift, nonsense, and splice site mutations and intragenic deletions. A mutation was found in 25 (86%) of the 29 familial cases and 8 (57%) of the 14 sporadic cases. Our data provide the first evidence that most of the familial and also a large number of the sporadic cases of hypophosphatemia are caused by loss-of-function mutations in PEX.[The sequence data described in this paper have been submitted to GenBank under accession nos. Y08111-Y08132 and Y10196.] X-linked dominant hypophosphatemic rickets [HYP; MIM 307800 (Mendelian inheritance in man number); McKusick 1994] has an incidence of 1 in 20,000 individuals and is the most common form of hypophosphatemia. The main physiological traits of the disease are a leak of phosphate from the kidney causing low phosphate levels in the blood and defective bone mineralization. Patients exhibit rickets and osteomalacia, lower extremity deformities, short stature, bone pain, dental abnormalities, and abnormal vitamin D metabolism. Several other less common disorders of inherited renal phosphate wasting also exist, including an autosomal dominant form (ADHR; McKusick 1994, MIM 193100;Econs and McEnery 1997) and hereditary hypophosphatemic rickets with hypercalciuria (HHRH; McKusick 1994, MIM 241530), which shows a complex inheritance pattern (Tieder et al. 1987). An additional tumor-induced form of hypophosphatemia exists, oncogenic hypophosphatemic osteomalacia, in which removal of the tumor leads to a return in normal phosphate levels (Fukomoto et al. 1979;Lobaugh et al. 1984;Weidner et al. 1985). These additional forms of the disease suggest that phosphate homeostasis is a complex process involving multiple gene products.Recently we cloned a candidate gene, PEX, for the X-linked dominant form of hypophosphatemic rickets, localized to the human Xp22 region (HYP GENOME RESEARCH 573Cold Spring Harbor Laboratory Press on May 10, 2018 -Published by genome.cshlp.org Downloaded from Consortium 1995). PEX has homologies to a family of zinc metalloproteases that includes neprilysin (NEP; D' Adamio et al. 1989), the Kell antigen (KELL; Lee et al. 1991) and endothelin-converting enzymes 1 and 2 (ECE-1 and ECE-2; Schmidt et al. 1994;Xu et al. 1994;Emoto and Yanagisawa 1995). NEP is known to inactivate a wide variety of peptide hormones, whereas ECE-1 and ECE-2 process inactive big endothelin 1 to its active form. A substrate for PEX has not yet been ...

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.