The long term goal of this revised project is to define the molecular basis of the genetic contributions to the development of alcoholism. The main objective is to determine the role of enzymes and receptors involved in dopaminergic neurotransmission in the development of severe alcoholism. Optimal segregation models are consistent with an autosomal dominant mode of transmission, but only with large differences in penetrance between males and females. At the present time, it is difficult to empirically test any of the proposed models of genetic transmission for alcoholism. Whether these specific transmission models are correct or not, one practical consequence is that genetic linkage studies using such models will have little power to detect or exclude linkage. The main reason is heterogeneity in phenotypes. This is a disadvantage of the linkage approach to alcoholism or other complex psychiatric disorders. This shortcoming of linkage analysis makes the use of association studies and DNA sequence analysis of candidate genes more attractive. Genomic DNA samples from 128 alcoholic probands, 88 psychiatrically normal controls, and 317 individuals in 36 alcoholic families will be typed for restriction fragment length polymorphisms (RFLPs) with cDNA clones of enzymes of the dopamine pathway and dopamine receptors. The exons of alleles of the genes in this pathway which show positive associations with alcoholism will be sequenced to detect DNA sequence variations. Finally, RFLP associations and DNA sequence variations will be tested for cosegregation with alcoholism in pedigrees. For any sequence variation, the role of the amino acid substitutions in altering enzymatic activity or receptor functioning will be clarified. These results may provide evidence for the role of any of the enzymes or receptors in the dopamine pathway in the development of alcoholism. The sequencing of intronic DNA near any disease associated sequence difference should allow the development of PCR based polymorphisms which can distinguish individuals carrying the mutant and normal genes. These would be useful in population studies to identify individuals at risk for developing alcoholism.
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