Further analysis of microsatellite marker in the BDNF gene

Brain-derived neurotrophic factor gene C-270T and Val66Met functional polymorphisms and risk of schizophrenia: a moderate-scale population-based study and meta-analysis

BACKGROUND

Lines of evidence have suggested that the brain-derived neurotrophic factor (BDNF) gene may be involved in the pathogenesis of schizophrenia. Two common functional polymorphisms C-270T and Val66Met within the BDNF gene were first reported by Kunugi et al. [Kunugi, H., Nanko, S., Hirasawa, H., Kato, N., Nabika, T., Kobayashi, S., 2003. Brain-derived neurotrophic factor gene and schizophrenia: polymorphism screening and association analysis. Schizophr. Res. 62, 281-283.] and pls expand this too: Hong et al. (2003) to be significantly associated with schizophrenia. However, subsequently several studies obtained conflicting results.

METHODS

We compared the allele/genotype frequencies of the C-270T and Val66Met polymorphisms and the haplotype frequencies at the two polymorphisms in a moderate independent patient-control sample from the Han Chinese population. Two systematic meta-analyses were performed to assess the collective evidence for association across studies for each of the two polymorphisms.

RESULTS

No statistically significant differences were found in allele or genotype or haplotype frequencies between patient and normal control subjects for either of the two polymorphisms. On the other hand, the meta-analysis of all published population-based association studies showed statistically significant evidence for heterogeneity among each of the two polymorphisms. Stratification of the studies by ethnicity of the samples yielded no significant evidence for an association with the polymorphisms in the Caucasian population (for C-270T polymorphism: pooled OR(Caucasian)=0.736, 95% CI=0.476-1.139, p=0.169; for Val66Met polymorphism: pooled OR(Caucasian)=1.027, 95% CI=0.796-1.325, p=0.835), nor in the Asian population (for C-270T polymorphism: pooled OR(Asian)=0.445, 95% CI=0.144-1.373, p=0.159; for Val66Met polymorphism: pooled OR(Asian)=0.962, 95% CI=0.820-1.128, p=0.635).

CONCLUSIONS

Our population-based study and meta-analysis demonstrate that the BDNF C-270T and Val66Met polymorphisms do not play major roles in the susceptibility to schizophrenia in either Caucasian or Asian populations. But we can not rule out the possibility that other polymorphisms with the BDNF gene are involved in the pathophysiology of schizophrenia.

A complex polymorphic region in the brain-derived neurotrophic factor (BDNF) gene confers susceptibility to bipolar disorder and affects transcriptional activity

Previous studies have suggested that genetic variations in the brain-derived neurotrophic factor (BDNF) gene may be associated with several neuropsychiatric diseases including bipolar disorder. The present study examined a microsatellite polymorphism located approximately 1.0 kb upstream of the translation initiation site of the BDNF gene for novel sequence variations, association with bipolar disorder, and effects on transcriptional activity. Detailed sequencing analysis revealed that this polymorphism is not a simple dinucleotide repeat, but it is highly polymorphic with a complex structure containing three types of dinucleotide repeats, insertion/deletion, and nucleotide substitutions that gives rise to a total of 23 novel allelic variants. We obtained evidence supporting the association between this polymorphic region (designated as BDNF-linked complex polymorphic region (BDNF-LCPR)) and bipolar disorder. One of the major alleles ('A1' allele) was significantly more common in patients than in controls (odds ratio 2.8, 95% confidential interval 1.5-5.3, P=0.001). Furthermore, a luciferase reporter gene assay in rat primary cultured neurons suggests that this risk allele (A1) has a lower-transcription activity, compared to the other alleles. Our results suggest that the BDNF-LCPR is a functional variation that confers susceptibility to bipolar disorder and affects transcriptional activity of the BDNF gene.

Brain-derived neurotrophic factor gene (BDNF) variants and schizophrenia: an association study

Polymorphisms in the brain-derived neurotrophic factor (BDNF) gene have been suggested to be associated with schizophrenia. In a replication attempt, Swedish patients with schizophrenia (n=187) and control subjects (n=275) were assessed for four BDNF gene polymorphisms. There were no significantly different allele, genotype or haplotype frequencies between cases or controls. Neither were there any differences when schizophrenic patients were sub-divided with regard to a number of different clinical variables, although a small group of psychotic patients with prominent affective features displayed higher frequencies of the less common alleles of the Val66Met and 11757 G/C polymorphisms compared to controls. The present Swedish results do not verify previous associations between putative functional BDNF gene polymorphisms and schizophrenia. However, when combined with previous studies meta-analyses indicated that the BDNF 270 T-allele and the Val66Met homozygous state were associated with the disorder. Thus, the BDNF gene may confer susceptibility to schizophrenia. Additional studies are warranted to shed further light on this possibility.

No association between the brain-derived neurotrophic factor gene and schizophrenia in a Japanese population

Brain-derived neurotrophic factor (BDNF) plays important roles in the survival, maintenance and growth of neurons. Several studies have indicated that BDNF is likely to be related to the pathogenesis of schizophrenia. Recent genetic analyses have revealed that BDNF gene polymorphisms are associated with schizophrenia, although contradictory negative findings have also been reported. To assess whether three BDNF gene polymorphisms (rs988748, C132T and rs6265) could be implicated in vulnerability to schizophrenia, we conducted a case-control association analysis (349 patients and 423 controls) in Japanese subjects. We found no association between these BDNF gene polymorphisms and schizophrenia using both single-marker and haplotype analyses. The results of the present study suggest that these three BDNF gene polymorphisms do not play major roles in conferring susceptibility to schizophrenia in a Japanese population. However, further studies assessing the associations between these BDNF gene polymorphisms and schizophrenia should be performed in several other ethnic populations.