Alcohol Dependence and Habitual Smoking: Risks : Part 2

by National Institute of Health

(Page 2 of 4)

The recruitment and assessment of study participants occurred in two stages. In stage I, the researchers recruited probands and family members as previously described and interviewed all participants to determine the presence of alcoholuse disorders, smoking, other drug dependence, and psychiatric disorders. The investigators used a diagnostic interview tool called the Semi-Structured Assessment for the Genetics of Alcoholism, which had been developed specifically for this study. Based on the interview, alcohol dependence was defined as meeting lifetime criteria for alcohol dependence as specified in the APA's DSM-III-R and the Feighner criteria for definite alcoholism.

In the initial assessment, the researchers did not evaluate the participants for nicotine dependence, but instead used habitual smoking as a proxy, which was defined as smoking 1 pack per day for at least 6 months. In a subset of study participants, however, the investigators conducted a full evaluation of nicotine dependence and found that 71 percent of habitual smokers also were nicotine dependent. The investigators used the information from the stage I sample to examine the risk of developing alcohol dependence or habitual smoking in families with alcohol-dependent members, as described in the following section.

To conduct more detailed analyses, the researchers subsequently selected a subset of families with at least three alcohol-dependent members as the stage II sample. For these families, the investigators also recruited more distant biological family members if a member from that branch of the family was alcohol dependent. For all stage II participants, researchers completed a more detailed evaluation and collected blood samples to obtain DNA for genetic studies. Thus, this stage II group of families that were severely affected with alcohol dependence was used for the genetic studies of alcohol dependence and habitual smoking discussed later in this article.

Transmission of Alcohol Dependence and Habitual Smoking in Families

The familial transmission of alcohol dependence and habitual smoking was examined in stage I families, specifically in the alcohol-dependent probands and their full siblings. The researchers did not include parents or children of the probands in this analysis in order to minimize external influences resulting from changes in drinking and smoking patterns across generations (changes in general attitudes toward drinking and smoking).

The study found that siblings of alcohol-dependent probands reported substantially higher rates for both alcohol dependence and habitual smoking than did the siblings of control probands. For example, almost one-half of the brothers and one-fourth of the sisters of alcohol-dependent probands had a lifetime diagnosis of alcohol dependence, rates that significantly exceeded those found in the general population (among the control sample). Similarly, habitual smoking was more common in the siblings of alcohol-dependent probands compared with the siblings of control probands. Thus, approximately 42 percent of brothers and 30 percent of sisters of alcohol-dependent probands reported habitual smoking, which again was significantly higher than among the siblings of control probands.

To examine whether the increased rate of habitual smoking among the siblings of alcoholic probands was mediated through an increased rate of alcohol dependence among those siblings themselves, the investigators examined the smoking rates of alcohol-dependent and non-alcohol-dependent siblings of alcoholics. If the increased rate of habitual smoking seen in siblings of alcoholics was mediated only through an increased rate of alcohol dependence, one would expect the rate of habitual smoking in the non-alcohol-dependent siblings to be the same as in the comparison sample. The study found, however, that compared with the community-based sample, an increased risk of habitual smoking existed even among non-alcoholdependent siblings, suggesting that factors in addition to an increased rate of alcohol dependence accounted for the siblings' risk of being habitual smokers. Indeed, part of this increased risk depended on the alcoholic proband also being a habitual smoker - that is, siblings of smoking alcoholic probands were at higher risks of smoking themselves than were siblings of nonsmoking alcoholic probands, indicating in part a specific familial transmission of habitual smoking.

Siblings share many characteristics that may be risk factors for the development of alcohol dependence and smoking. The COGA investigators therefore analyzed the data to evaluate the effects of multiple potentially confounding characteristics on the risk of developing habitual smoking or alcohol dependence. According to these analyses, characteristics that strongly predicted an increased risk of alcohol dependence included the sibling's gender, birth cohort, and history of other drug dependence, as follows.

Sisters of alcoholic probands were significantly less likely to be alcohol dependent than were brothers. Furthermore, sisters were less likely to be habitual smokers compared with brothers; however, this difference was not as pronounced as with alcohol dependence.

Birth cohort significantly influenced the rates of alcohol dependence and habitual smoking among the siblings of alcoholic probands. For example, siblings born between 1950 and 1959 were approximately 63 percent as likely, and siblings born in 1960 or later were approximately 50 percent as likely, to become habitual smokers than were siblings born before 1950. Conversely, alcohol dependence became more common in more recent generations. Thus, siblings born between 1950 and 1959 were 1.5 times more likely, and siblings born in 1960 or later were two times more likely, to be diagnosed with alcohol dependence than were siblings born before 1950. These findings are consistent with the strong trends in smoking and alcohol dependence in the general population, for which the rate of smoking has been decreasing and the rate of alcohol dependence has been increasing in younger generations.

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