Aim. The aim of this study was to specify the genotype and allele frequency of the 3'UTR VNTR DAT polymorphism in patients with schizophrenia and healthy controls. Both patients and healthy controls were divided into smaller subgroups based on the gender differences and the age of onset.
Method. The studied group comprised 362 unrelated patients with schizophrenia (205 males and 157 females) and 376 controls (150 males and 226 females). 69 patients developed schizophrenic symptoms at the age of 18 or earlier. All individuals participating in this study were Polish, mostly from the Wielkopolska region. For each patient, a consensus diagnosis was made by two psychiatrists using the Structured Clinical Interview for DSM-IV Axis I Disorders (SCID). Genotyping of the 3'UTR VNTR DAT polymorphism was performed using the PCR-VNTR method. Statistical analysis of genotype and allele frequencies was performed with the Pearson's x² and Fisher's exact tests, respectively. Additionally, an analysis of the power estimation as well as the concordance between the genotype distribution and the Hardy-Weinberg equilibrium was performed.
Results. The association between male schizophrenics and A9/A9 and A9/Al0 genotypes (p = 0,004) and A9 allele (p = 0,00l) was observed. Comparing patients with early onset of schizophrenia with controls, the association was also detected for genotypes A9/A9 and A9/A10 (p = 0,002) and for A9 allele (p = 0,003). Additionally, there was a statistically significant difference in the genotype frequency between patients with early and late onset of schizophrenia (p = 0,004).
Conclusions. The present results show a possible association between an increased susceptibility to early onset of schizophrenia in males and the A9 allele and genotypes containing this allele (A9/A9 and A9/A10).