Brain-derived neurotrophic factor (BDNF) has been implicated in the pathogenesis of schizophrenia and bipolar disorder. A functional polymorphism Val66Met of BDNF gene was studied in patients with schizophrenia (n=336), bipolar affective disorder (n=352) and healthy controls (n=375). Consensus diagnosis by at least two psychiatrists, according to DSM-IV and ICD-10 criteria, was made for each patient using a structured clinical interview for DSM-IV Axis I disorders (SCID). No association was found between the studied polymorphism and schizophrenia or bipolar affective disorder either for genotype or allele distribution (for genotype: p=0.210 in schizophrenia, p=0.400 in bipolar disorder; for alleles: p=0.260 in schizophrenia, p=0.406 in bipolar disorder). Results were also not significant when analysed by gender. For males genotype distribution and allele frequency were (respectively): p=0.480 and p=0.312 in schizophrenia, p=0.819 and p=0.673 in bipolar affective disorder. Genotype distribution and allele frequency observed in the female group were: p=0.258 for genotypes, p=0.482 for alleles in schizophrenia; p=0.432 for genotypes, p=0.464 for alleles in bipolar affective disorder. A subgroup of schizophrenic (n=62) and bipolar affective patients (n=28) with early age at onset (18 years or younger) was analysed (p=0.328 for genotypes, p=0.253 for alleles in schizophrenia; p=0.032 for genotypes, p=0.858 for alleles in bipolar affective disorder).

There is evidence for an association between polymorphisms of monoamine transporter genes and temperamental personality traits. Recent findings have shown that interaction of allelic variants of the different genes may contribute to the personality factors. We studied the association between temperamental personality dimensions measured with the Temperament and Character Inventory (TCI) and polymorphisms of the dopamine (DAT), norepinephrine (NET) and serotonin (5-HTT) transporter genes in 127 healthy Polish volunteers. There were no significant differences between means of TCI temperamental dimensions (novelty seeking, reward dependence, persistence and harm avoidance) and the transporter genes compared by ANOVA. There were some significant associations between genotypes and TCI subdimensions. Individuals carrying the A9/A9 DAT genotype have lower RD4 scores (dependence vs. independence) than A10/A10 individuals (3.0 ± 1.4 vs. 3.5 ± 1.3); p = 0.01. Examining 5-HTT gene promoter polymorphism, heterozygous individuals (l/s) and individuals with 44-bp deletion (s/s) scored significantly lower in the HA1 subdimension (anticipatory worry and pessimism vs. uninhibited optimism; 4.3 ± 2.3 vs. 5.5 ± 2.6) in comparison with individuals without deletion (l/l); p = 0.021. The NET transporter gene polymorphism showed no significant association with any of the temperamental TCI subdimensions.

The associations between 5-HTT-linked polymorphic region (5-HTT-LPR), monoamine oxidase A (MAOA)-LPR and the dimensions of temperament evaluated using the Temperament and Character Inventory (TCI) and NEO Five-Factor Inventory (NEO-FFI) were studied. One hundred healthy volunteers (without psychiatric disorders) were recruited to represent a cross-section of the population of Szczecin (Poland) in terms of sex, age and education. No associations between 5-HTT-LPR and the TCI harm avoidance dimension and between 5-HTT-LPR and the NEO-FFI neuroticism dimension were found. Males carrying the 3-VNTR MAOA gene variant (209 bp) had significantly lower values on the NEO-FFI openness dimension (p = 0.039) and obtained higher scores on the subdimension 3 of the TCI reward dependence (RD3), i.e. attachment vs. detachment (p = 0.005). Individuals carrying the ‘short’ variant of 5-HTT-LPR had lower values on the reward dependence dimension and the RD4 subdimension (dependence vs. independence) than individuals not carrying the ‘short’ variant (p = 0.039 and p = 0.011, respectively). Females carrying the ‘short’ variant had lower values on NS1 (exploratory excitability vs. stoic rigidity) and RD4 (dependence vs. independence) than those not carrying the variant (p = 0.042 and 0.043, respectively). The obtained level of significance with respect to the observed associations between 5-HTT-LPR and the reward dependence scales and subscales and between 5-HTT-LPR and the NS1 subscale are too weak for further interpretation. Our results do not confirm the hypothesis that there is a simple correlation between single gene polymorphisms and a personality trait measured by the TCI and NEO-FFI scales.

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