No abstract

P450 oxidoreductase (POR) is the obligatory flavoprotein intermediate that transfers electrons from reduced nicotinamide adenine dinucleotide phosphate (NADPH) to all microsomal cytochrome P450 enzymes. Although mouse Por gene ablation causes embryonic lethality, POR missense mutations cause disordered steroidogenesis, ambiguous genitalia, and Antley-Bixler syndrome (ABS), which has also been attributed to fibroblast growth factor receptor 2 (FGFR2) mutations. We sequenced the POR gene and FGFR2 exons 8 and 10 in 32 individuals with ABS and/or hormonal findings that suggested POR deficiency. POR and FGFR2 mutations segregated completely. Fifteen patients carried POR mutations on both alleles, 4 carried mutations on only one allele, 10 carried FGFR2 or FGFR3 mutations, and 3 patients carried no mutations. The 34 affected POR alleles included 10 with A287P (all from whites) and 7 with R457H (four Japanese, one African, two whites); 17 of the 34 alleles carried 16 "private" mutations, including 9 missense and 7 frameshift mutations. These 11 missense mutations, plus 10 others found in databases or reported elsewhere, were recreated by site-directed mutagenesis and were assessed by four assays: reduction of cytochrome c, oxidation of NADPH, support of 17alpha-hydroxylase activity, and support of 17,20 lyase using human P450c17. Assays that were based on cytochrome c, which is not a physiologic substrate for POR, correlated poorly with clinical phenotype, but assays that were based on POR's support of catalysis by P450c17--the enzyme most closely associated with the hormonal phenotype--provided an excellent genotype/phenotype correlation. Our large survey of patients with ABS shows that individuals with an ABS-like phenotype and normal steroidogenesis have FGFR mutations, whereas those with ambiguous genitalia and disordered steroidogenesis should be recognized as having a distinct new disease: POR deficiency.

Claudins are major components of tight junctions and contribute to the epithelial-barrier function by restricting free diffusion of solutes through the paracellular pathway. We have mapped a new locus for recessive renal magnesium loss on chromosome 1p34.2 and have identified mutations in CLDN19, a member of the claudin multigene family, in patients affected by hypomagnesemia, renal failure, and severe ocular abnormalities. CLDN19 encodes the tight-junction protein claudin-19, and we demonstrate high expression of CLDN19 in renal tubules and the retina. The identified mutations interfere severely with either cell-membrane trafficking or the assembly of the claudin-19 protein. The identification of CLDN19 mutations in patients with chronic renal failure and severe visual impairment supports the fundamental role of claudin-19 for normal renal tubular function and undisturbed organization and development of the retina.

No abstract