Nineteen heterogeneous subunits of the GABAA receptor (6 α, 3 β, 3 γ, 1 δ, 1 ε, 1 θ, 1 π and 3 ρ) have been identified (Belelli and Lambert, 2005), with 70% sequence homology within classes and 30% homology between classes. Functional receptors are pentameric, with the receptor usually comprised of 2 α subunits, 2 β subunits, and one γ subunit. Genetic variation in genes coding receptor subunits, including, for example, variants affecting exon splicing mechanisms (Barnard et al., 1998; Sieghart and Sperk, 2002; Simon et al., 2004), may be responsible for differences in receptor composition and therefore differences in multimeric receptor properties, including location in the neuron, change in sensitivity to neurotransmitter, kinetics of the channel, other pharmacological and physiological properties, and expression patterns (Belelli and Lambert, 2005).
