Molecular characterization of new polymorphisms at the beta2, alpha1, gamma2 GABA(A) receptor subunit genes associated to a rat nonpreferring ethanol phenotype

Recent preclinical and clinical studies have indicated a possible involvement of the genes encoding for the GABA(A) receptor subunits alpha6, beta2, alpha1 and gamma2 in the genetic susceptibility to alcohol abuse. We have recently found an (R) to (Q) mutation in codon 100 of the alpha6 GABA(A) subunit, that segregated in a rat line selectively bred for its voluntary ethanol aversion, Sardinian alcohol nonpreferring (sNP), but not in their Sardinian alcohol preferring (sP) counterpart, selected for its ethanol preference. In the present study the molecular composition of other GABA(A) subunits (beta2, alpha1 and gamma2) were analyzed in order to further investigate the involvement of the GABA(A) receptors in the genetic predisposition to voluntary alcohol intake. Automated sequencing analysis indicated the presence of six new silent substitutions (289 T-->C in the beta2 gene; 115 G-->A in the alpha1 gene; 157 G-->A, 174 C-->T, 347 A-->G and 385 A-->T in the gamma2 gene), in sNP but not in sP rats. These polymorphisms were linked to the alpha6 R100Q mutation previously described in sNP rats. The strict association between the alpha6 point mutation and the new polymorphisms found in the beta2, alpha1 and gamma2 genes, demonstrate that such genes belong to the same cluster and are inherited together in the rat. These results sustain the synteny for these clusters between the rodent and human genomes, and suggest that mutated GABA(A) beta2, alpha6, alpha1 and gamma2 subunit genes might contribute to the expression of an ethanol nonpreferring phenotype in a rat line that voluntarily avoids alcoholic solutions.