Abstract: | We demonstrated previously that an α1—β2—γ2 gene cluster of the γ-aminobutyric acid (GABAA) receptor is located on human chromosome 5q34–q35 and that an ancestral α—β—γ gene cluster probably spawned clusters on chromosomes 4, 5, and 15. Here, we report that the α4 gene (GABRA4) maps to human chromosome 4p14–q12, defining a cluster comprising the α2, α4, β1, and γ1 genes. The existence of an α2—α4—β1—γ1 cluster on chromosome 4 and an α1—α6—β2—γ2 cluster on chromosome 5 provides further evidence that the number of ancestral GABAA receptor subunit genes has been expanded by duplication within an ancestral gene cluster. Moreover, if duplication of the α gene occurred before duplication of the ancestral gene cluster, then a heretofore undiscovered subtype of α subunit should be located on human chromosome 15q11–q13 within an α5—αx—β3—γ3 gene cluster at the locus for Angelman and Prader—Willi syndromes. |