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Article Excerpt
IN THE UNITED STATES, more than 80% of persons admitted to treatment programs for alcohol problems experienced their first alcohol intoxication between the ages of 12 and 18 (Substance Abuse and Mental Health Services Administration, 2003). Alcohol dependence symptoms typically develop during adolescence and young adulthood (Nelson et al., 1996), and the earlier an adolescent commences drinking, the greater the odds of developing alcohol abuse and dependence (Grant et al., 2001). Using the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV; American Psychiatric Association, 1994), large population-based studies have shown that 9.6% of adolescents meet the criteria for lifetime alcohol abuse and 3.9% of adolescents for lifetime alcohol dependence (Chung et al., 2002). Because the development of alcohol abuse and dependence begins in adolescence, it is important to gain understanding into the etiology of these disorders in adolescent populations.
Problem alcohol use, including alcohol abuse and dependence, aggregates in families. Family members of probands with problem alcohol use are at increased risk for problem use compared with families of controls (Miles et al., 1998). Similarly, parental problem alcohol use increases the risk of alcohol abuse and dependence in offspring (Jacob et al., 2003). Twin and adoption studies examining alcohol abuse and dependence have found that the familial nature of these disorders is moderately attributable to shared genes, with heritability estimates typically ranging from 40% to 60% (e.g., Cadoret et al., 1985; Hopfer et al., 2001; Kendler et al., 1994; McGue, 1997; Prescott and Kendler, 1999). Several studies have also found that shared environmental factors play a substantial role, although these influences weaken with age (see Hopfer et al. [2003a] for a review). Thus, it is well established that alcohol abuse and dependence is familial, with approximately half of the familial aggregation from genetic influences. However, studies of familial aggregation and genetic influence have largely been conducted in adult samples.
Little is known about familial influences on adolescent alcohol abuse or dependence. The few studies of adolescent samples have typically examined alcohol use rather than abuse or dependence. Of 35 family, twin, and adoption studies examining alcohol-use behaviors, only 12 examined adolescents. Of those 12, 9 focused on alcohol use, and 3 examined alcohol abuse or dependence. These 3 studies focused on examining the covariation between alcohol abuse or dependence (not both) and other psychiatric disorders such as conduct disorder, depression, and other drug use (Hicks et al., 2004; Rose et al., 2004; Stallings et al., 1997). Thus, no studies have explicitly examined familial influences on adolescent alcohol abuse or dependence.
A limitation of the current research on familial influences on adult and adolescent alcohol abuse and dependence is that the studies have typically relied on the assessment of dyadic relationships such as parent and offspring or pairs of twins; few studies have examined the transmission of problem alcohol use in the entire family. Examining children and parents together can be a powerful method to understand the family transmission of alcohol-use disorders. For example, Kendler et al. (1994) employed a parents-of-twins design and found that genetic vulnerability to problem alcohol use was equally transmitted from mothers and fathers and that familial resemblance for problem alcohol use was attributed to genes. Using an offspring-of-twins design, Jacob et al. (2003) examined abuse and dependence in male twins, their adolescent and young-adult offspring, and the mothers of the offspring. They found that the offspring of an unaffected monozygotic twin whose co-twin was alcohol dependent was no more likely to exhibit abuse or dependence than the offspring of control twins, suggesting that the absence of parental problem alcohol use can moderate the impact of high genetic risk. However, the above studies focused mainly on adults and their families rather than on adolescents.
Another important factor often overlooked in family and twin studies of problem alcohol use is assortative mating; that is, the tendency for persons with problem alcohol use to marry one another more often than would be expected by chance. Random mating is one of the basic assumptions in twin modeling, despite evidence of marital assortment for problem alcohol use (Hall et al., 1983; Stallings et al., 1997). Problem alcohol use in both parents serves to increase both genetic and environmental risk in their offspring (Vanyukov and Tarter, 2000). In addition, assortative mating tends to increase the similarity of dizygotic twins relative to monozygotic twins, thereby inflating estimates of shared environmental contributions and underestimating genetic contributions (Allison et al., 1996; Krueger et al., 1998). For these reasons, it is important to include the effects of assortative mating into models that examine family resemblance of alcohol problems. Other potentially important influences often overlooked in family and twin studies are environmental influences specific to siblings and not transmitted from parents: these "horizontal" influences include shared peer influences, cohort effects, and sibling interactions. A study examining marijuana abuse and dependence in adolescents found evidence of significant horizontal transmission among siblings (Hopfer et al., 2003b), suggesting that these influences may be important, particularly for adolescents.
A final issue of importance is the method of ascertainment of the samples used in...
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