Despite the recognition that genetic factors play an important role in susceptibility to alcohol dependence (AD), few genes have been identified to date that have been replicated across studies. Because alcohol dependence is a common disorder affecting one in five men and one in twelve women, the prevailing thought has been that common genetic variants (those with minor allele frequency over 3% in the population) would be the appropriate place to look for susceptibility variants. The common disease/common variant hypothesis has provided the impetus for a large number of genome-wide association studies (GWAS) where a large number of common variants have been assessed. While some studies have reported findings meeting genome-wide significance, often the findings for AD cannot be replicated in other studies. Also, across a wide variety of diseases, it is now recognized that only 2-4% of the variance in disease outcome is explained by these common variants. Recent evidence suggests that variants that are rarer may be more penetrant and potentially explain a greater proportion of disease outcome. Members of families in which multiple cases of AD are seen are most likely to carry a burden of rare and highly penetrant risk variants. Using existing DNA collected from members of high density AD pedigrees, we will use next generation exome sequencing and novel bioinformatics tools to identify rare variation in these high risk individuals and examine the distribution of variants in the families in collaboratin with the Center for Human Genetic Variation at Duke.
Aim 1 provides a discovery stage and is facilitated by the use of a subset of pedigrees in which DNA is available for parents and affected offspring.
Aim 2 provides confirmation of the discovered variation using a larger set of pedigrees in which the existence of the variants and their distribution within the full pedigree will be determined. By focusing on individuals with a strong genetic burden with multigenerational involvement and including the entire exome, we expect to find rare highly penetrant variants that would be undetectable with other approaches. A search for early developmental indicators of AD susceptibility has revealed both clinical (e.g., presence of childhood conduct disorder) and biological endophenotypes (e.g., reduced amplitude of the P300 component of the event-related potential).
In Aim 3, we will examine our newly discovered rare variants in a third generation sample of individuals followed from childhood through young adulthood and for whom developmental trajectories of P300 amplitude are available. This sample includes both high-risk offspring from multiplex for AD families and low-risk controls providing an opportunity to find variants associated with P300 trajectories, an endophenotype that is highly associated with AD.
Alcohol dependence is a highly heritable condition that is estimated to affect 17.6 million persons in US, often with devastating health consequences for the individual and substantial cost to society. The proposed study seeks to increase our understanding of the genetic basis of the disease by performing exome sequencing (sequencing of all of the exons or protein coding portion of genes in the genome) in members of pedigrees selected for a high density of alcohol dependence where DNA for parents, affected and unaffected offspring exists. By focusing on families with multiple members with alcohol dependence who are most likely to carry an elevated burden of rare, highly penetrant genetic risk factors, and perform exome sequencing, we expect to find rare genetic variants that would not be detectable with other approaches. Moreover, common variants can also be detected with the proposed method. Results of this study could potentially indicate novel and important targets for pharmacotherapies for alcohol dependence and provide a better understanding of developmental indicators of alcohol dependence risk.
| Sharma, Vinod K; Hill, Shirley Y (2017) Differentiating the Effects of Familial Risk for Alcohol Dependence and Prenatal Exposure to Alcohol on Offspring Brain Morphology. Alcohol Clin Exp Res 41:312-322 |
| O'Brien, Jessica W; Hill, Shirley Y (2017) Neural predictors of substance use disorders in Young adulthood. Psychiatry Res Neuroimaging 268:22-26 |
| Hill, Shirley Y; Rompala, Gregory; Homanics, Gregg E et al. (2017) Cross-generational effects of alcohol dependence in humans on HRAS and TP53 methylation in offspring. Epigenomics 9:1189-1203 |
