Genetics of addictions

Investigating CHRNA5, CHRNA3, and CHRNB4 variants in the genetic landscape of substance use disorder in Jordan

BACKGROUND

Substance use disorder (SUD) is a complex illness that can be attributed to the interaction between environmental and genetic factors. The nicotinic receptor gene cluster on chromosome 15 has a plausible association with SUD, particularly with nicotine dependence.

METHODS

This study investigated 15 SNPs within the CHRNA5, CHRNA3, and CHRNB4 genes. Sequencing was used for genotyping 495 Jordanian males with SUD and 497 controls matched for age, gender, and descent.

RESULTS

Our findings revealed that none of the tested alleles or genotypes were correlated with SUD. However, our analysis suggests that the route of substance use was linked to rs1051730 (P value = 0.04), rs8040868 (P value = 0.01) of CHRNA3, and rs16969968 (P value = 0.03) of CHRNA5. Additionally, a correlation was identified between rs3813567 of the CHRNB4 gene and the age at substance use onset (P value = 0.04).

CONCLUSIONS

Variants in CHRNA5, CHRNA3, and CHRNB4 may interact with SUD features that can influence the development and progression of the disorder among Jordanians.

MAOA uVNTR Polymorphism Influence on Older Adults Diagnosed with Diabetes Mellitus/Systemic Arterial Hypertension

Background

Monoamine oxidase (MAO) is involved in several biological processes associated with well-being and mental health, and alterations in its function might directly impact various mental disorders. Some mental disorders concomitantly occur in individuals with clinical characteristics, such as substance abuse and diabetes.

Objective

To analyze the functional MAOA uVNTR polymorphism genotype frequency in an older adult population with diabetes mellitus/arterial hypertension and associate this frequency with clinical characteristics impacting daily life. Methodology. Older adults diagnosed with diabetes mellitus, systemic arterial hypertension, or both (DM/SAH) were selected and had their MAOA gene genotyped for uVNTR polymorphism. The revised Beck Depression Inventory (BDI) and a questionnaire were also applied to determine their mental health and clinical characteristics.

Results

The allelic variants detected among the participants were the 2R, 3R, 4R, and 3R/4R heterozygous genotypes. Genotypes solely containing the 3R allele had patients who marked yes for smoking and alcoholism, and only those with the 3R genotypes (female 3R/3R homozygote or male 3R∗ hemizygote) were significant. Although not statistically significant, only 3R and 3R/4R genotypes presented cases of severe depression per the revised BDI interpretations.

Conclusion

The MAOA uVNTR polymorphism's low-activity 3R allele presence in an older adult population diagnosed with DM/SAH may represent a risk for developing substance use (alcohol and smoking) dependence.

Informing Prevention and Intervention Policy Using Genetic Studies of Resistance

The common paradigm for conceptualizing the influence of genetic and environmental factors on a particular disease relies on the concept of risk. Consequently, the bulk of etiologic, including genetic, work focuses on "risk" factors. These factors are aggregated at the high end of the distribution of liability to disease, the latent variable underlying the distribution of probability and severity of a disorder. However, liability has a symmetric but distinct aspect to risk, resistance to disorder. Resistance factors, aggregated at the low end of the liability distribution and supporting health and recovery, appear to be more promising for effective prevention and intervention. Herein, we discuss existing work on resistance factors, highlighting those with known genetic influences. We examine the utility of incorporating resistance genetics in prevention and intervention trials and compare the statistical power of a series of ascertainment schemes to develop a general framework for examining resistance outcomes in genetically informative designs. We find that an approach that samples individuals discordant on measured liability, a low-risk design, is the most feasible design and yields power equivalent to or higher than commonly used designs for detecting resistance genetic and environmental effects.

A haplotype analysis is consistent with the role of functional HTR1B variants in alcohol dependence

BACKGROUND

Animal and human studies have suggested that the serotonergic system plays an important role in alcohol consumption and abuse, mainly due to the serotonin receptor 1B (5-HT(1B)) function in the mesolimbic reward pathway. Association studies between the HTR1B gene variants and alcoholism have found significant results. There is also evidence for a complex balancing regulation of the gene by two functional variants in the promoter region (rs11568817 and rs130058), which are in linkage disequilibrium.

METHODS

The aim of this study is to investigate the role of the most relevant variants (rs11568817, rs130058, rs6296 and rs13212041) of the HTR1B gene in the susceptibility to alcohol dependence. The sample comprised 136 Brazilian alcoholics of European descendent and 237 controls.

RESULTS

The results suggest an association between a functional variant of the gene (rs11568817) and alcohol dependence (p=0.001). In addition, this association could also be confirmed in an independent sample using imputed data from a GWAS, where marginal significant association (p=0.03, one-tailed) with the same allele was obtained. The pattern of distribution of haplotypes was significantly different between patients and controls (p<0.0001), which is consistent with the role of the two functional variants of the promoter region.

CONCLUSION

In conclusion, our findings point to an association between functional variants in the promoter region of the HTR1B gene and alcohol dependence, supporting previous neurobiological evidences of the involvement of HTR1B variations in alcohol-related phenotypes.