We are searching for genetic loci that contribute to the predisposition to alcoholism and related behaviors by conducting genetic linkage and mapping analyses using over 500 highly polymorphic DNA marker loci. These loci span all of the non-sex chromosomes at an average interval less than 10 centimorgans. To date, we have completed over 300,000 locus typings, primarily on American Indians and Finns. A whole autosomal genome scan for genetic linkage to alcohol dependence in a Southwestern American Indian tribe was performed. The best evidence for linkage is seen with D11S1984 on chromosome 11p, in close proximity to several candidate genes with neurobiological functions. These candidate genes include the DRD4 dopamine receptor gene, the tyrosine hydroxylase gene, and the tryptophan hydroxylase gene. Good evidence for linkage is also seen with D4S3242 on chromosome 4p, nearby the beta1 GABA receptor gene. The chromosome 11 findings were followed up by genotyping a high resolution map on an expanded sample of subjects from the same Southwestern Indian population. The high resolution genetic map includes polymorphisms within the DRD4 and tyrosine hydroxylase genes as well as STR markers closely linked to these candidate genes. We are also developing statistical approaches and software for identifying which specific polymorphisms from a set of closely linked loci are responsible for altering an individual's vulnerability to disease. In Finns, association between alcohol dependence and Y-chromosomes was statistically significant. Interestingly, there is no association between Y- chromosomes and antisocial personality disorder after the comorbid effects of alcohol dependence were removed. However, we find evidence for genetic linkage and association between antisocial personality disorder (ASPD) occurring with alcoholism and the chromosome 6 serotonin receptor gene HTR1B. We also find evidence for linkage and association between ASPD with alcoholism and a polymorphism in the closely linked marker locus D6S286. These findings are confirmed by multipoint linkage analyses and by independent observations in the Southwestern Indian sample. We are conducting a two-stage full autosomal genome linkage scan on the Finnish families. This approach is being taken in order to minimize laboratory analyses while retaining statistical power. Stage I. Two hundred eighty two individuals are being genotyped for a panel of 256 microsatellite loci. These marker loci span the autosomal genome at an average density of 13.2 cM (largest gap = 25 cM). The 282 individuals belong to 112 informative full sibships from 89 pedigrees. Most loci in this panel segregate tetra-nucleotide repeat alleles. More than 230 loci have been typed on the Stage I sample since January 1, 2000. Genotypings are being performed on Perkin Elmer / Applied Biosystems 373A and 377 DNA sequencers using routine methods. Two standard DNA samples are run on every gel in order to facilitate calibration of amplicon size estimates across gels. In addition, 1 out of every 22 DNA samples is a quality control sample whose identity is hidden from the laboratory genotyping personnel. Our genotyping error rate is less than 1.6% based on over 2327 duplicated typings of these quality control samples. Our success rate of PCR amplification exceeds 95%. Two-point and multi-point linkage analyses are being performed on these data using a linkage method that simultaneously utilizes information from unaffected, discordant, and affected sib-pairs. Preliminary analyses indicate that the genomic region most likely to harbor a gene for alcohol dependence resides on chromosome 11p. Stage II. The genomic regions identified in Stage I with the most promising evidence for loci linked to alcoholism and related phenotypes will be selected for follow-up. New microsatellite loci will be added to the existing marker map to increase the marker density in the most promising regions. In addition, statistical power will be enhanced by genotyping all family members. This will provide more precise estimates of allelic identity by descent. It will also provide many pairs of distant relatives who contribute linkage information to the variance-components and pedigree based linkage methods.
Showing the most recent 10 out of 11 publications
