The human metabotropic glutamate receptor 8 (GRM8) gene: a disproportionately large gene located at 7q31.3-q32.1.

Metabotropic glutamate receptors (GRMs), which constitute a family of genes, are neurotransmitter receptors that respond to glutamate stimulations by activating GTP-binding proteins and modulating second-messenger cascades. Pharmacological and expression studies of the rodent Grm8 gene suggest it could be a presynaptic receptor modulating glutamate release at the axon terminals. To study human GRM8, we have determined its nucleotide sequence and genomic organization. While the coding region of the gene spans only 2.3 kb, the gene encompasses approximately 1000 kb of DNA at the boundary of the q31.3-q32.1 bands of chromosome 7. This observation is relevant to the study of Smith-Lemli-Opitz syndrome and an autosomal dominant form of retinitis pigmentosa (RP10), since they map to the same region.