Use of recombinant inbred strains for studying genetic determinants of responses to alcohol

A recently-developed method of gene mapping is reviewed. Several responses to EtOH were studied with the purpose of identifying genes with modest effects (Quantitative Trait Loci, or QTLs). As an example, results from a study of acute ethanol withdrawal severity are discussed. Mice from inbred strains C57BL/6J and DBA/2J, and 19 of their Recombinant Inbred (BXD RI) strains, were given 4 g/kg EtOH and their acute withdrawal severity assessed with the handling-induced convulsion (HIC). HIC scores varied markedly among strains. Comparison of the pattern of strain means for withdrawal with a database comprising genotype of each BXD RI strain for almost 800 mapped polymorphic genetic markers revealed associations with several potential QTLs appearing on several mouse chromosomes. To verify the presence of a gene affecting withdrawal, we then withdrawal-tested individual F2 mice bred from the F1 cross of the parental C57 and DBA strains. These mice were then genotyped for several polymorphic markers close to a putative QTL on chromosome 2. Possession of the DBA allele in severely withdrawing F2 animals was significantly associated with one such marker, D2Mit9, confirming the presence of a gene nearby affecting withdrawal. As a further test, mice of the replicated Withdrawal Seizure-Prone (WSP) and -Resistant (WSR) lines, selected for severity of EtOH withdrawal HIC, were also genotyped. Alleles at the D2Mit9 locus assorted disproportionately (and consistently) between the two pairs of WSP and WSR lines, while alleles at other loci did not. Thus, three tests consistently suggest the influence of a gene, tentatively termed Aw1, 37 cM from the centromere on chromosome 2, that appears to control as much as 40% of the genetic variance in withdrawal. The provisional locus is located very near to two candidate genes. Gad1 codes for the synthesis of glutamic acid decarboxylase, the rate-limiting enzyme for synthesis of GABA. A cluster of genes (Scn1, Scn2, Scn3) code for voltage-sensitive sodium channel proteins. These genes are plausible candidates for affecting withdrawal HIC.