Alcohol use is an established facet of diverse cultural contexts and religions, providing perceived pleasure to many users and facilitating social interaction. However, excessive alcohol use is also a principal causal factor in a number of mental health conditions, including alcohol dependence and other alcohol use disorders (1). According to the WHO global status report on alcohol and health in 2018, alcohol dependence (identified as an impairment of self-control over his or her drinking) is often associated with mental health problems such as depression (2). Further studies have shown that alcohol dependence significantly increases the risk of suffering from depression (3, 4). Alcohol use disorder is characterized by repeated withdrawals, followed by relapses, resumption of drinking. Alcohol dependent withdrawal (ADW) is caused by a cessation of long-term ethanol consumption and is characterized by symptoms of hyperactivity of the central nervous system, hyperactivity of the autonomic nervous system, causing physical and emotional disorders (5). ADW-related mood disorders, including depression, anxiety, irritability, are a significant cause of alcohol dependence relapse (6–8). However, reports on the effect of ADW and the onset and emergence of depression varies greatly across individuals (9).

The literature on alcohol dependence withdrawal indicates that not all individuals experience symptoms of depression in the context of ADW. Several depression studies indicate that more than 50% of depression patients have experienced severe adversity before the onset of the illness, while some people facing severe stress never have symptoms of depression (10, 11). For example, Caspi et al. found subjects with short allele of 5-HTTLPR (homozygotes or heterozygotes) exhibited more depressive symptoms and had more possibility to diagnose as depression than individuals with long allele homozygotes of 5-HTTLPR when exposed to life stress (12). To further investigate factors that lead to differences in the development of depression on an individual level, depression and alcoholism studies began to investigate the association of polymorphisms in various genetic regions of alcohol dependent subjects (13–15). Amongst cyclic AMP (cAMP), protein kinase A, cAMP responsive element-binding, and neuropeptide Y (NPY), the role of NPY in the development of depression within the context of alcohol dependence is well-established (13, 15–17). NPY, a highly conserved 36-residue peptide, is reported to be densely distributed in amygdala, hippocampus, neocortex and other areas related to psychopathology, playing a pivotal role in regulating emotion response (18). Many studies have shown that the expression level of NPY in the brain is closely related to the occurrence of depression. For example, people with low levels of NPY in the brain have a higher risk of depression (19). Conversely, administration of NPY have anti-stress effects, and thereby can reduce emotional responses on depression (20).

Single nucleotide polymorphisms (SNPs) are genetic variants of one nucleotide and these changes could have functional implications. On the one hand, SNPs can influence rates of transcription causing changes in the production of encoded protein when present in regulatory sites of a gene. On the other hand, in the coding regions, SNPs can alter protein structure and hence function, resulting in the development of disease or change in response to a drug or environmental toxin (21). Thus, researchers have used SNPs as biomarkers in many disease genetics and pharmacogenomic studies. Located on chromosome 7p15.3, the human NPY gene has four exons, of which rs16147 is the main genetic variant described in this gene and it is located within the promoter region upstream of the NPY gene (22). Previous studies have identified NPY rs16147:T>C, a single promoter variant, responsible for the expression of NPY (15). Furthermore, it reported that NPY rs16147:T>C genotypes were associated with stress experiences, which can predict stress-related outcomes. In animal models, NPY reduces stress effects (20, 23) and alcohol consumption (24), and opposes the actions of corticotropin-releasing factor (CRF) (25) as well as responsible for the anxiogenic and stress-like consequences of alcohol dependence withdrawal (16).

Yet to date, few studies have examined the exact form of the interaction between the environment and NPY rs16147:T>C gene polymorphism. According to the literature on gene-by-environment (G × E) interactions, the interaction between environment and gene polymorphism can be fitted into two model. The diathesis-stress model of environmental action (26) suggests individuals with a risk gene are affected negatively by poor environments, whereas individuals with a different version of the same gene are relatively unaffected by environments. Where given the best environments, individuals with differing polymorphisms may exhibit similar levels of behavior, but behavior of the groups diverges with worsening environmental conditions. The differential-susceptibility model (27) on the other hand, suggests that individuals carrying “risk alleles” may simply be more malleable to changes in the environment. Wherein, individuals with a putative high-risk allele should exhibit poorer outcomes in poor environments and similar outcomes to individuals with a low-risk allele in average environments. However, in very good environments, individuals with a putative high-risk allele will show outcomes that are superior to individuals with the low-risk allele. In other words, individuals with “risk alleles” are malleable to environment conditions, benefitting from supportive environments but exhibiting poorer outcomes in poor environments.

The present study aims to understand the role of NPY rs16147:T>C on depression in patients with acute alcohol dependence withdrawal. According to the literature on alcohol dependence and depression, NPY rs16147:T>C is key to understanding the development of depression in alcohol dependence withdrawal population (28). Yet to date, the exact form of the interaction between the environment and NPY rs16147:T>C gene polymorphism remains unclear. To further understand the role of NPY rs16147:T>C, blood samples and scores of Michigan Alcoholism Screening Test (MAST), self-depression scale (SDS) were obtained from alcohol dependence patients from seven psychiatric hospitals. Confirmatory analytic approaches commonly used in previous studies were then conducted to identify the form of G × E interaction. Specifically to identify whether the role of NPY rs16147:T>C conforms to the diathesis-stress model or the differential-susceptibility model. Based on the current literature suggesting that T alleles of rs16147:T>C are protective under high stress conditions (15). It could be hypothesized that NPY rs16147:T>C may accord with the differential-susceptibility model, wherein NPY rs16147:T>C under very good environment conditions may show outcomes that are superior to individuals with the low-risk allele; but poorer outcomes in poor environments and similar outcomes in average environments compared to low-risk allele.

Alcohol dependence was assessed using MAST (13). The MAST is a self-report questionnaire comprising 25 items rated on a scale from 1 to 4, with a higher number corresponding to greater alcohol dependence. The scale has high internal consistency reliability, with an alpha value of 0.90 (15).

SDS was used to assess each participant's level of depression. The SDS contains 20 items that are rated on a scale from 1 to 4, with higher numbers corresponding to more frequent symptoms. The higher the total score, the more severe the depressive symptoms (17). Considering that the ADW patients are able to cooperate in answering the questionnaire about 20 days later, SDS is used to measure the severity of depressive symptoms 3 weeks after hospitalization.

Genomic DNA was extracted from each blood sample using standard techniques. The NPY rs16147:T>C was conducted using the TaqMan SNP genotyping assay (cat number: 4351374; ABI: Applied Biosystems Inc., Foster City, CA, USA). The probes of SNPs were analyzed from ABI assay on demand kit.

First, the Hardy–Weinberg equilibrium for genotype distributions of NPY rs16147:T>C was tested using the c2 test for goodness of fit. Then, Pearson correlations were examined between genetic polymorphisms, age, years of education, alcohol dependence, and depression. Consistent with other research, CT and TT genotypes were collapsed into a T-allele group and coded as 1; the CC genotype was coded as 0. Then, traditional linear regression was used to test the interaction between alcohol dependence and the rs16147:T>C polymorphism. When a significant interaction was found, region of significance (RoS) analysis was used to examine the form of the interaction (29).

Finally, a re-parameterized regression model was fitted to examine the specific pattern of gene × environment pattern (30), which had the form:

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