A 3-Mb map of a large Segmental duplication overlapping the alpha7-nicotinic acetylcholine receptor gene (CHRNA7) at human 15q13-q14.

Several neuropsychiatric disorders map to human 15q13-q14, which contains a strong candidate in the alpha7-nicotinic acetylcholine receptor subunit gene (CHRNA7) and is partly duplicated, complicating further genetic analysis. We have shown that the partial duplication is in a hybrid (CHRFAM7A)between CHRNA7 and one of many copies of a novel gene (FAM7A). We have constructed a 3-Mb map of 15q13-q14 showing that CHRFAM7A is part of a large segmental duplication in the opposite orientation to CHRNA7 and revealing several other duplications. The data support a model of recent evolutionary events including duplications, at least one large deletion, and an inversion. We have identified two individuals with a structure that lacks CHRFAM7A and therefore predates many steps in this model, suggesting an unstable region with other intermediates possibly still in existence. This instability may be relevant to the many neuropsychiatric disorders that map in this region.