Genome-wide association meta-analysis of age at first cannabis use

BACKGROUND AND AIMS

Cannabis is one of the most commonly used substances among adolescents and young adults. Earlier age at cannabis initiation is linked to adverse life outcomes, including multi-substance use and dependence. This study estimated the heritability of age at first cannabis use and identified associations with genetic variants.

METHODS

A twin-based heritability analysis using 8055 twins from three cohorts was performed. We then carried out a genome-wide association meta-analysis of age at first cannabis use in a discovery sample of 24 953 individuals from nine European, North American and Australian cohorts, and a replication sample of 3735 individuals.

RESULTS

The twin-based heritability for age at first cannabis use was 38% [95% confidence interval (CI) = 19-60%]. Shared and unique environmental factors explained 39% (95% CI = 20-56%) and 22% (95% CI = 16-29%). The genome-wide association meta-analysis identified five single nucleotide polymorphisms (SNPs) on chromosome 16 within the calcium-transporting ATPase gene (ATP2C2) at P < 5E-08. All five SNPs are in high linkage disequilibrium (LD) (r2  > 0.8), with the strongest association at the intronic variant rs1574587 (P = 4.09E-09). Gene-based tests of association identified the ATP2C2 gene on 16q24.1 (P = 1.33e-06). Although the five SNPs and ATP2C2 did not replicate, ATP2C2 has been associated with cocaine dependence in a previous study. ATP2B2, which is a member of the same calcium signalling pathway, has been associated previously with opioid dependence. SNP-based heritability for age at first cannabis use was non-significant.

CONCLUSION

Age at cannabis initiation appears to be moderately heritable in western countries, and individual differences in onset can be explained by separate but correlated genetic liabilities. The significant association between age of initiation and ATP2C2 is consistent with the role of calcium signalling mechanisms in substance use disorders.

Predictors of cannabis and tobacco co-use in youth: exploring the mediating role of age at first use in the population assessment of tobacco health (PATH) study

Background

Adolescents often use substances such as tobacco and cannabis. Co-use of these substances can lead to physical, mental, and psychosocial difficulties beyond that which would be anticipated by simple additivity of their individual effects.

Methods

We aimed to examine the mediating role of age at first use of cannabis or tobacco (AU) between youth factors of internalizing, externalizing, and sensation seeking and two co-use outcomes (lifetime; last 30 days). Path analytic modeling using data from youth age 12–17 who had tried cannabis or tobacco at least once in their lives and participated in the Population Assessment of Tobacco Health (PATH) waves one and two (collected 2013–2015; n=3,847; approximately 46% female) study allowed us to examine these relationships.

Results

The lifetime use model indicated significant direct (internalizing (B = 0.18), externalizing (B = 0.30), sensation seeking (B = 0.15)) and indirect relationships (internalizing (B = 0.18), externalizing (B = 0.33), sensation seeking (B = 0.10)) between each of the three youth factors, the mediator (AU) and the lifetime co-use outcome (p < 0.05 for all). A direct relationship between AU and lifetime co-use was also observed (B = − 1.54). In the past 30-day use model, significant direct paths from AU (B = − 0.49) and sensation seeking (B = 0.06) to past 30-day use were present (p < 0.05 for all).

Discussion

Examination of mediation by AU in the relationships between youth factors and youth co-use of cannabis and tobacco is an important step in understanding these complex relationships. This study is strengthened by the use of a large, nationally representative sample, yet is limited by several factors, such as the use of a secondary dataset and the use of youth self-report.

Conclusions

Based on the findings, programs or interventions targeting youth factors of internalizing, externalizing, and sensation seeking as well as interventions aiming to stave off AU should promote decreased tobacco and cannabis co-use. Sensation seeking and AU appear to be the most influential factors and should be considered when developing and promoting prevention policies/programs for higher risk youth populations.

Investigation on the association between breast cancer and consumption patterns of combined oral contraceptive pills in the women of Isfahan in 2011

BACKGROUND

Oral contraceptive pills are among the most popular contraceptive methods, but the fear of cancer and cardiovascular disease overshadows its continuous use among women. This study aimed to define the association between consumption patterns of combined oral contraceptives among women with breast cancer.

MATERIALS AND METHODS

This is an analytical case-control study conducted on 175 women with breast cancer, referring to Seyed al Shohada Medical Center and private clinics in Isfahan to be treated and followed up in 2011, as well as 350 healthy women who were identical with the subjects in the study group regarding age and residential location. The data were collected using a researcher-made questionnaire. Content validity and Cronbach's alpha were employed to confirm validity and scientific reliability of the questionnaire, respectively. The data were analyzed by descriptive and analytical statistical methods through SPSS.

RESULTS

The findings showed that there was a significant association between history of contraceptive pills' consumption and incidence of breast cancer (P < 0.001). It was shown that the risk of developing breast cancer is increased by 2.27-fold among those with pills' consumption compared to those with no history of that. It was also shown that pills' consumption for 36-72 months increased the risk of breast cancer by 2.18-fold, the age of the first use being less than 20 years increased the risk by 3.28-fold, and time since the last use of less than 25 years increased the risk by 2.63-fold. There was no significant association between duration of use, age of the first and last use, and time since the first and last use in the study and control groups.

CONCLUSION

The results showed that history of pills' consumption is associated with incidence of breast cancer regardless of the consumption pattern. Use of oral contraceptives pills at any age and for any duration can increase the risk of breast cancer.