Genomic Association/Linkage of Sodium Lithium Countertransport in CEPH Pedigrees

Abstract

Abstract-Little is known about genetic determinants explaining variation in the erythrocyte sodium-lithium countertransport (SLC), an intermediate phenotype of essential hypertension. We characterized the SLC in immortalized lymphoblasts and showed that its behavior is similar to that of erythrocyte SLC. We then performed association and linkage analyses of the SLC in immortalized lymphoblasts from 5 large pedigrees from the Center d'Etude du Polymorphisme Humain (CEPH) genomics repository. The results of these analyses showed that a number of genomic regions harboring genes involved in glutathione metabolism might explain variations in SLC activity. The activity of SLC is modified by thiol alkylating agents, such as maleimide, which increases the affinity of the SLC to Li ϩ . 1,2 Although the kinetics of the SLC are well characterized, the nature of the transporter and the genes contributing to its expression are unknown. Evidently, functional properties of the SLC 3 and its gene(s) 4,5 are different from those of the ubiquitous Na ϩ /H ϩ -antiport (NHE-1). Thus, a search for genes that explain variation in SLC activity is in order. The discovery of these genes may have clinical relevance because the SLC is one of the most studied intermediate phenotypes of essential hypertension. The National Library of Medicine lists Ͼ500 peerreviewed papers that have explored the epidemiology and physiology of the SLC in the context of essential hypertension and related cardiovascular diseases. The activity of the SLC, as expressed in erythrocytes in vivo, has been shown to correlate with a host of cardiovascular risk factors that relate to essential hypertension, including insulin resistance and dyslipidemia. 6 -9 In addition, the activity of the SLC is lower in blacks than in whites 10 -12 (for review, see Aviv and Lasker 13 ) and is lower in white women than in white men. 14,15 Importantly, the activity of the SLC reflects both genetic and environmental factors. 14 -16 In the present study, we describe a novel strategy for dissecting the genetic basis of the SLC by shielding it from influences owing to different environmental conditions that exist in vivo, and by taking advantage of the vast amount of publicly available genotype data. We accomplished this by studying the SLC in Epstein-Barr virus (EBV)-immortalized lymphoblasts of large reference Center d'Etude du Polymorphisme Humain (CEPH) pedigrees. The CEPH collection provides a considerable advantage in that extensive genotype data are already available for some of the pedigrees in the CEPH (http://landru.cephb.fr) and the companion Coriell Cell Repositories (http://locus.umdnj.edu/nigms/ceph/ceph.html). By screening cell lines from CEPH pedigrees for variations in the SLC, we were able to rapidly use this enormous amount of genotype data. Materials and Methods Accessing the CEPH PedigreesLymphoblasts from the members of 5 CEPH pedigrees were obtained from the CEPH and the Coriell Cell Repositories. These repositories contain information on Ͼ12 000 DNA microsatell...

Model-fitting and linkage analysis of sodium–lithium countertransport

“…Possibly 10 þ additional loci underlie the remaining 55 -60% of the genetic variance, assuming each contributes less than the TG-responsive locus. The numerous marker associations 18 reported also support the presence of many genes. ADD1 may be one of the additional genes, although, if so, we lacked sufficient power for confirmation.…”

“…5 Although failing the suggestive linkage threshold, D10S1221 (lod ¼ 1.75) and D8S2324 (lod ¼ 1.55) fall on the Marshfield map o1 and 1.1 cM, respectively, from markers D10S122 and D8S1475 found to associate with SLC. 18 Standard segregation analysis of SLC on this sample inferred major locus inheritance in only the pedigrees ascertained through coronary heart disease, but not stroke or hypertension, 4 motivating the inclusion herein of multiple loci to model genetic heterogeneity. In a previous attempt to dissect the heterogeneity, segregation analysis of principal component (PC) scores supported major locus inheritance of three scores to which SLC contributed substantially.…”

“…17 Genome-wide association analysis of SLC in immortalized lymphoblasts identified multiple associations, many with markers near genes involved in glutathione metabolism. 18 Herein, we analyzed SLC measured twice at a 2 -3 years interval on members of 48 pedigrees. We tested for association with ADD1 and apoE polymorphisms, fit genetic models, and tested for linkage to genome-wide markers.…”

A human Na + /H + antiporter sharing evolutionary origins with bacterial NhaA may be a candidate gene for essential hypertension

“…Sequence similarity with Escherichia coli NhaA (EcNhaA) served to guide functional characterization by heterologous expression in yeast. Patterns of tissue distribution, chromosomal location, and inhibitor sensitivity point to this gene as a likely candidate for the sodium-lithium countertransport (SLC) activity reported in red blood cells (11), lymphoblasts, and fibroblasts (12)(13)(14), and suggest an important potential physiological role in hypertension.…”

Genome-wide discovery of loci influencing chemotherapy cytotoxicity

“…The CEPH resource is an easily accessible collection of multigeneration families, on which extensive microsatellite and singlenucleotide polymorphism genotype data are freely available (11)(12)(13). This experimental platform provides a unique opportunity for the application of familial genetic strategies to cancer pharmacogenomic discovery, allowing for the rigorous testing of samples from multiple families under identical conditions.…”