Although prior studies have suggested a genetic commonality of ADHD and alcoholism, the study found no significant contribution of two specific candidate genes, the promoter polymorphism of the serotonin transporter gene (5-HTT) and the 5-HT2c receptor Cys23Ser polymorphism.
"Our results indicate that individuals with persisting ADHD symptoms in adulthood seem to be at high risk of developing an alcohol-use disorder," said Monika Johann, medical doctor and research associate at the University of Regensburg and first author of the study. "Moreover, there is evidence for a highly increased severity of alcohol dependence in subjects with ADHD."
Researchers examined 314 adult alcoholics (262 males, 52 females) as well as 220 unrelated healthy control subjects, all of German descent. Each participant was assessed for psychiatric disorders, such as substance-use disorders (including alcoholism), ADHD, and antisocial personality disorder (APD). Patients with a history of major psychiatric disorders, including depression and schizophrenia, and those with addictions to drugs other than alcohol and nicotine, were excluded from the investigation. Genotyping was performed without knowledge of diagnostic status, with a focus on the 5-HTT promoter and the 5-HT2c Cys23Ser polymorphism.
"Prior neuroendocrine challenge studies with a drug called fenfluramine in subjects with ADHD or alcoholism revealed similar differences in the serotonergic neurotransmission when compared to normal subjects," explained Johann. "The usual response to fenfluramine administration is a measurable increase in the circulating prolactin. This usual increase is blunted in subjects with ADHD or alcoholism. The main structures responsible for the fenfluramine-induced prolactin release are the 5-HTT and the 5-HT2c receptors. Therefore, both seemed plausible as overlapping sources of genetic liability of ADHD and alcoholism."
Neither of them, however, appear to be genetic risk factors in the sample examined. "Our data demonstrate that the 5-HTT promoter and the 5-HT2c Cys23Ser polymorphism do not contribute to the putative common genetic predisposition for ADHD and alcohol dependence," said Johann. "However, several other candidate genes have yet to be investigated."
Nonetheless, the findings do indicate a distinct phenotype, a way to measure an observable trait or behavior.
Part Two: High Risk Group
