Inheritance of a defect in a neuronal mechanism that regulates response to auditory stimuli was studied in nine families with multiple cases of schizophrenia. The defect, a decrease in the normal inhibition of the P50 auditoryevoked response to the second of paired stimuli, is associated with attentional disturbances in schizophrenia. Decreased P50 inhibition occurs not only in most schizophrenics, but also in many of their nonschizophrenic relatives, in a distribution consistent with inherited vulnerability for the illness. Neurobiological investigations in both humans and animal models indicated that decreased function of the ␣7-nicotinic cholinergic receptor could underlie the physiological defect. In the present study, a genome-wide linkage analysis, assuming autosomal dominant transmission, showed that the defect is linked [maximum logarithm of the odds (lod) score ‫؍‬ 5.3 with zero recombination] to a dinucleotide polymorphism at chromosome 15q13-14, the site of the ␣7-nicotinic receptor. Despite many schizophrenics' extremely heavy nicotine use, nicotinic receptors were not previously thought to be involved in schizophrenia. The linkage data thus provide unique new evidence that the ␣7-nicotinic receptor gene may be responsible for the inheritance of a pathophysiological aspect of the illness.

Although linkage disequilibrium with other genetic alterations cannot be excluded, the CHRNA7 core promoter variants, found in this study, may contribute to a common pathophysiologic feature of schizophrenia.

No abstract

Linkage of a neurophysiological deficit associated with schizophrenia, i.e., the failure to inhibit the auditory P50 response, was previously reported at chromosome 15q14. The marker with the highest pairwise lod score, D15S1360, was isolated from a yeast artificial chromosome containing a candidate gene, the ␣7-nicotinic acetylcholine receptor gene. In the present study, this linkage was further investigated in a subset of the NIMH Genetics Initiative schizophrenia families. These families have not been studied neurophysiologically, as were the families in the original report. Therefore, the DSMIII-R diagnosis of schizophrenia was used as the affected phenotype. Twenty families fulfilled the criteria of at least one sibpair concordant for schizophrenia, along with their two parents or another affected relative outside the nuclear family, available for genotyping. Sibpair analysis s h o w e d a s i g n i f i c a n t p r o p o r t i o n o f D15S1360 alleles shared identical-bydescent (0.58; P < 0.0024). The results further support the involvement of this chromosomal locus in the genetic transmission of schizophrenia. Am.

The transmission/disequilibrium test was used for fine mapping of the linkage of schizophrenia to the chromosome 15q13-14 region, the site of a candidate gene, the alpha7 nicotinic acetylcholine receptor subunit gene (CHRNA7), in parent-child triads from the NIMH Schizophrenia Genetics Initiative families. This candidate gene was identified from neurobiological studies of deficits in schizophrenics of the inhibitory gating of the P50 auditory evoked potential. The neurobiological deficit was also used as a phenotype for subsequent linkage analysis. In the present study, significant genotype-wise disequilibrium (P < 0.007) was found at D15S165, a polymorphic simple sequence marker physically located within 1 megabase of both CHRNA7 and a partially duplicated, expressed sequence that includes exons 5-10 of CHRNA7. Replication of this result was found in an additional set of families. The results support this region as a chromosomal location involved in the genetic transmission of schizophrenia.

The transmission/disequilibrium test was used for fine mapping of the linkage of schizophrenia to the chromosome 15q13-14 region, the site of a candidate gene, the alpha7 nicotinic acetylcholine receptor subunit gene (CHRNA7), in parent-child triads from the NIMH Schizophrenia Genetics Initiative families. This candidate gene was identified from neurobiological studies of deficits in schizophrenics of the inhibitory gating of the P50 auditory evoked potential. The neurobiological deficit was also used as a phenotype for subsequent linkage analysis. In the present study, significant genotype-wise disequilibrium (P < 0.007) was found at D15S165, a polymorphic simple sequence marker physically located within 1 megabase of both CHRNA7 and a partially duplicated, expressed sequence that includes exons 5-10 of CHRNA7. Replication of this result was found in an additional set of families. The results support this region as a chromosomal location involved in the genetic transmission of schizophrenia.