QPRT and early-onset autosomal dominant Alzheimer disease: Of these a few appear to be particularly interesting, including the nicotinic cholinergic receptor subunit gene CHRNA7, and QPRT, which codes for quinolinate phosphoribosyltransferase, an enzyme involved in metabolizing an endogenous exitotoxin (quinolinate) implicated in Alzheimer Disease and Huntington Disease.