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We have mapped a sample of 68 families consisting of one or more affected sibling pairs with schizophrenia or schizoaffective disorder with 20 markers spanning all of chromosome 15 to investigate whether there is a locus on chromosome 15 that confers an increased susceptibility to schizophrenia using parametric and nonparametric linkage analyses. Allele sharing identical by descent and multipoint maximum likelihood score (MLS) statistics were employed. Results show excess allele sharing for multiple markers in 15q11.2-q25, a chromosomal region previously found linked to a decrease in the normal inhibition of the P50 auditory-evoked response to the second of paired stimuli, a decrease associated with schizophrenia. Excess allele sharing was found for markers spanning about 48 cM in 15q11.2-q25 (D15S1002-D15S1023). The greatest single point allele sharing was found at D15S659 (62.6%). The multipoint MLS scores were greater than 1.0 in the 30-52 cM interval delimited by ACTC and D15S150, with a maximum value of 2.0 with GENEHUNTER PLUS near D15S1039.

Our results do not support the speculation that the Gs-alpha protein gene has a role in the genetic predisposition to bipolar disorder.