'Robust' Features of Alcohol Dependence Identified

Findings May Lead to More Accurate Diagnosis

Deborah Brauser

June 23, 2011

June 23, 2011 — Diagnosing lifetime history of alcohol dependence (LTH-AD) disorder can be challenging, but new research identifies specific factors that may help improve diagnostic reliability.

In a population-based study of more than 4000 male twins, investigators found that the heritability of LTH-AD in the study population was 71%. In addition, such characteristics as a high number of AD symptoms and long episode duration correlated with an accurate diagnosis.

However, the commonly used Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-4), assessment of LTH-AD, with a single interview, was found to be only relatively reliable. This is because the general public often underestimates associations when asked to report on experiences of psychiatric or substance use disorders.

"The most obvious reason for this is that people just don't recall when prompted," said lead author Eivind Ystrom, PhD, from the Department of Adult Mental Health at the Norwegian Institute of Public Health in Oslo.

Dr. Eivind Ystrom

"Thus, by interviewing [them] several times about the same disorder, it is possible to estimate to what extent they are inaccurate," said Dr. Ystrom.

The study was published online June 15 in Alcoholism: Clinical & Experimental Research.

Some Symptoms More Predictive Than Others

Investigative team member Alexis Edwards, PhD, from the Virginia Institute of Psychiatric and Behavioral Genetics at Virginia Commonwealth University in Richmond, noted that the identification of certain features that "robustly" predicted diagnosis dependability is what makes this study unique.

"Obviously all of the symptoms are, at some level, predictive of the disorder. But that some are more useful than others at identifying a reliable diagnosis is interesting," said Dr. Edwards in a release.

"While the reliability of the diagnosis itself is moderate, results show that we can potentially increase our confidence in the diagnosis by taking into account these few specific variables," she added.

"AD is one of the main challenges in public health; 6.5% of the total disease burden in European countries can be attributed to alcohol use," said Dr. Ystrom.

He noted that previous studies have found that AD "is somewhere between" 50% and 100% heritable.

"It was important to establish where it lay, [but] if we don't know the reliability of AD, we cannot be sure about heritability."

Genetic Vulnerability

For this study, the investigators evaluated data on 4203 male twins (including 231 individuals without their co-twin; 100% white) from the Virginia Adult Study of Psychiatric and Substance Use Disorders.

All participants were interviewed and assessed for LTH-AD by phone or in person on 2 separate occasions that were approximately a year apart. Genetic and environmental influences on the disorder were also examined.

Results showed that an individual's specific environment accounted for approximately 29% of the causes for LTH-AD, whereas heritability accounted for the remaining percentage.

"The higher heritability of the LTH-AD phenotype, which is a bit higher than we might have expected, confirms the importance of genetic influences," said Dr. Edwards.

"By estimating the heritability to 71%, the study moves AD into a class of disorders that are highly dependent on genes, such as schizophrenia or bipolar disorder," added Dr. Ystrom.

"It is significant to know that much of the reason why this happens to people is because of individual genetic vulnerability."

The reliability of the DSM-4 LTH-AD diagnosis alone was judged to be moderate (kappa = 0.54).

However, the reliability was significantly higher for the participants when the following characteristics were taken into account: increased symptom number; treatment-seeking at some point in their life; increased time spent obtaining, using, or recovering from alcohol use; and a long duration for their most severe episode.

"Since the study identifies which characteristics are associated with a reliable diagnosis, they can then be used to enhance the reliability of single measures of LTH-AD," said Dr. Ystrom.

"Clinicians need to be confident that a patient truly has a disorder before embarking on a treatment program, whether that involves counseling, pharmaceutical treatment, or something else."

Dr. Ystrom said he hopes to next look into risk indicators of AD, especially mental health and age of alcohol use initiation.

"I also want to look into how stressful life events relate to the genetic vulnerability to AD."

The study was funded in part by grants from the National Institutes of Health. The study authors have disclosed no relevant financial relationships.

Alcohol Clin Exp Res. Published online June 15, 2011.



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