Genetic variants in the CPNE5 gene are associated with alcohol dependence and obesity in Caucasian populations

Highlights

• 10 SNPs in CPNE5 associated with alcohol dependence (AD) and 12 SNPs with obesity.

• The most significant SNP associated with AD was rs998617 with p = 9.72 × 10⁻⁵.

• The most significant SNP associated with obesity was rs10456444 with p = 1.01 × 10⁻³.

• 6 SNPs associated with both AD and obesity in the Marshfield sample.

• Calcium (Ca²⁺) may be one of the mechanisms linking between AD and obesity.

Abstract

Alcohol addiction may increase the risk of obesity due to shared genetic components. The Copine V (CPNE5) gene is involved in Ca²⁺ binding and may play an important role in the development of the central nervous system. This study tested the genetic associations of 77 single-nucleotide polymorphisms (SNPs) within the CPNE5 gene with alcohol dependence (AD) and obesity using a Caucasian sample – The Study of Addiction – Genetics and Environment (SAGE) sample (1066 AD cases and 1278 non-AD controls, 422 obese cases and 1395 non-obese controls). The Marshfield sample (1442 obese cases and 2122 non-obese controls) was used for replication of obesity. Multiple logistic regression analysis was performed using the PLINK software. In the SAGE sample, we identified 10 SNPs associated with AD and 17 SNPs associated with obesity (p < 0.05). Interestingly, 6 SNPs (rs9986517, rs9470387, rs3213534, rs10456444, rs3752482, and rs9470386) were associated with both AD (OR = 0.77, 0.77, 0.83, 0.84, 0.79 and 1.14, respectively; p = 9.72 × 10⁻⁵, 1.1 × 10⁻⁴, 4.09 × 10⁻³, 5.26 × 10⁻³, 1.59 × 10⁻², and 3.81 × 10⁻², respectively) and obesity (OR = 0.77, 0.77, 0.78, 0.77, 0.68 and 1.18, respectively; p = 2.74 × 10⁻³, 2.69 × 10⁻³, 2.45 × 10⁻³, 1.01 × 10⁻³, 5.18 × 10⁻³ and 3.85 × 10⁻², respectively). In the Marshfield sample, rs3752480 was associated with obesity (p = 0.0379). In addition, four SNPs (rs9986517, rs10456444, rs7763347 and rs4714010) showed associations with obesity in the meta-analysis using both samples (p = 0.00493, 0.0274, 0.00346, and 0.0141, respectively). These findings provide the first evidence of common genetic variants in the CPNE5 gene influencing both the AD and obesity; and will serve as a resource for replication in other populations.

Introduction

Alcohol consumption is the third leading risk factor globally for disease burden, and harmful use of alcohol leads to 2.5 million deaths worldwide every year (WHO, 2010). In the United States (US), 71% of the general US aged 18 or older reported that they drank in the past year. One quarter (24.6%) reported engaging in binge drinking, and 7.1% reported heavy drinking in the past month (SAMHSA, 2012). Based on the 2009–2010 National Health and Nutrition Examination Survey (NHANES) data, the age-adjusted obesity prevalence among US adults 20 years and older was 35.7% (Flegal et al., 2012), with the absolute numbers of obese individuals globally projected to surpass 1.12 billion by 2030 (Kelly et al., 2008). Previous epidemiological data suggest that moderate alcohol intake may protect against obesity, particularly in women, whereas higher consumption including binge-drinking may increase the risk of obesity (Wilson, 2010, Yeomans, 2010, Wakabayashi, 2014). Results are inconsistent, however. For example, one study suggested that heavy drinking was not related to obesity (Adachi et al., 2000), with another study reporting frequent drinking was associated with reduced odds of obesity (Rohrer et al., 2005). Using the 1988–1994 NHANES data in the non-smoking US adult population, the odds of overweight and obesity were significantly higher among binge drinkers and those consuming four or more drinks/day. However, those who reported drinking one or two drinks per day, or less than five drinks per week, had decreased odds of obesity (Arif and Rohrer, 2005). One recent study using the NHANES registry of 1999–2002 suggested potential gender differences in the link between alcohol consumptionand obesity. Binge drinking was associated with significantly higher odds of obesity, for both males and females, however, moderate drinking (3 drinks/day in females and 4 drinks/day in males) was associated with increased odds of obesity in females, but decreased odds of obesity in males (Chakraborty, 2014).

Alcohol dependence (AD) is a psychiatric diagnosis evidenced by physical or psychological dependence on alcohol. According to the Diagnostic and Statistical Manual of Mental Disorders (DSM) IV criteria for AD, at least three out of seven of the following criteria must be manifest during a 12-month period: tolerance, withdrawal symptoms, use in larger amounts or for longer periods than intended, persistent desire, loss of control, reduction or cessation of social, occupational and recreational pursuits, continued use despite knowledge of alcohol-related harm. (http://www.alcoholcostcalculator.org/business/about/dsm.html). Among American adults, approximately 12% have had an AD problem in their lifetime, with 4% classified as having an AD problem in the previous 12-months (Hasin et al., 2007). Family, twin, and adoption studies have indicated that genetic and environmental factors, as well as their interactions, all contribute to the development of AD, with a heritability of more than 0.5 (Heath et al., 1997, Schuckit, 2000, Goldman et al., 2005, Bierut et al., 2010). Recently, several genome-wide association studies (GWAS) have been completed and a number of candidate genes have been found to be associated with the risk of AD and alcohol consumption (e.g., Bierut et al., 2010, Edenberg et al., 2010, Schumann et al., 2011, Wang et al., 2011, Zuo et al., 2012, Gelernter et al., 2014).

Binge eating disorder, and overeating as an addictive disorder, are also psychiatric disorders in DSM-V and are often comorbid with obesity (James et al., 2004, Volkow and O'Brien, 2007, American Psychiatric Association, 2013). Alcohol addiction may also be comorbid with obesity, and those with AD may be at increased risk of obesity due to shared genetic components (Wang et al., 2013).

The Copine V (CPNE5) (also known as CPN5, COPN5) gene is located at 6p21.2 (Creutz et al., 1998, Tripodis et al., 1998). Copines are a family of calcium-dependent lipid-binding proteins comprised of 2 N-terminal C2 domains (C2Ds) and a C-terminal A domain. The C2Ds contain aspartate residues important for calcium and phospholipid binding (Ramsey et al., 2008). The CPNE5 is one of several genes that encode a calcium-dependent protein containing two N-terminal type II C2 domains and an integrin A domain-like sequence in the C-terminus. A recent study showed that CPNE5 is expressed in both neural progenitor cells and the differentiated neurons during the neural development, suggesting that CPNE5 might play an important role in the development of the central nervous system (Ding et al., 2008). Although alcohol's effects on the central nervous system, including neuro-cognitive deficits, neuronal injury and neurodegeneration, are well documented, the biological and genetic mechanisms remain elusive (Mukherjee, 2013). Hence, CPNE5 is a suitable candidate gene for study in AD. In the present study, we hypothesized that CPNE5 plays a role in AD, with some genetic variants within the CPNE5 gene potentially associated with both AD and obesity. This study explored the associations of 77 single-nucleotide polymorphisms (SNPs) within the CPNE5 gene with both AD and obesity in The Study of Addiction – Genetics and Environment (SAGE) sample (1066 AD cases and 1278 non-AD controls, 422 obese cases and 1395 non-obese controls). The Marshfield sample (1442 obese cases and 2122 non-obese controls) was used for replication of obesity.