Objectives:
Introduction. The combined type of ADHD and alcohol dependence are two different disorders. Research demonstrates that 45-55% of patients diagnosed with ADHD also suffer from comorbid substance abuse, and 11-55% of patients diagnosed with substance abuse suffer from undiagnosed ADHD. Alcohol is by far the most widely used psychoactive substance in the European culture. The serotonin transporter (5HHT) gene has been implicated as one of the candidate genes in both disorders in recent molecular genetic research. Aim of study. The aim of the present study was to seek a common clinical and biological marker for hyperkinetic disorder and youth drinking.

Methods:
Methods. The study was conducted at the Department of Psychiatry, Pomeranian Medical University, Szczecin (Poland) between 2008 and 2012. The sample consisted of 100 combined type ADHD patients, 51 adolescents youth drinking and 100 individuals without mental disorders or addiction in a population-based group. The 5HHT gene polymorphism was examined using PCR (Polymerase Chain Reaction).

Results:
Results. A preferential trend for the “s” short allele of the investigated 5HHT gene polymorphism was observed in all the groups of adolescents compared to the population-based group of adults without alcohol dependence (p=0.01).

Conclusions:
Conclusions: Based on the conducted study a provisional conclusion may be drawn that the presence of the short “s” allele of the 5HHT gene polymorphism may be a prognostic factor of impulsivity in ADHD and of predisposition to alcohol dependence.