Human Na plus /H plus exchanger genes - Identification of polymorphisms byradiation hybrid mapping and analysis of linkage in end-stage renal disease

The Na+/H+ exchangers (NHEs) are membrane-bound transporters that catalyze the electro-neutral movement of extracellular Na+ for intracellular Ht. NHE genes play a critical role in pH homeostasis and cellular volume regulatio n and can be considered candidate genes for essential hypertension and rena l disease. This study was performed to determine whether the NHE genes cont ributed to genetic susceptibility ill end-stage renal disease (ESRD). To da te, 5 isoforms of NHE have been cloned in mammals (NHE1 to NHE5). The compl ementary DNA (cDNA) sequences of NHE1 to NHE3 and NHE5 are known in humans. Because the chromosomal structure of the NHE genes is unknown, we used cDN A sequences to design polymerase chain reaction primers for use in radiatio n hybrid mapping. Radiation hybrid mapping of NHE genes identified nearby p olymorphic markers for NHE1 to NHE3 (NHE1, D1S197, D1S2677; NHE2: D2S373, D 2S1789; and NHE3, D5S678, D5S2005), We used these markers, and other previo usly identified polymorphic markers for NHE5, in linkage and association an alyses of ESRD. The NHE1 to NHE3 and NHE5 loci did not demonstrate evidence for linkage to ESRD. However, NHE5 showed significant evidence for associa tion (P less than or equal to 1.0x10(-4)). The strongest evidence for assoc iation was observed with allele 6 of NHE5 (P less than or equal to 0.001 to 0.01). Allele 6 appeared to have a renoprotective effect, with a frequency of 0.15 in the control population and 0.06 to 0.09 in patients with ESRD, The combined approach of designing primers from cDNA and radiation hybrid m apping has proven successful in identifying polymorphisms for human genes o f which only cDNA sequences were previously available. The NHE primers and associated polymorphic loci identified in this study can be used in genomic , linkage, and association analysis of NHE genes in future genetic studies of hypertension and renal failure. Given the allelic association, further e valuation of the role of NHE5 in ESRD susceptibility appears warranted.