Table 1.
Studies on BDNF/DNA modifications and circulating mRNA levels.
| Study and Country | Study Design | Sample | Study Aim(s) | Main Findings | |
|---|---|---|---|---|---|
| 1 | Dell’Osso, 2014, Italy [48] | Cross-sectional | 144 patients (43 MDD; 61 BD I; 50 BD II); 44 HC |
To investigate differences in BDNF promoter gene methylation in patients with mood disorders |
Higher methylation levels in BD II (compared to BD I) and MDD patients (compared to controls). Lower methylation levels in patients during mania/mixed episodes compared to the depressive phase. |
| 2 | Li et al. 2014, China [44] | Longitudinal |
203 patients with a first major depressive episode
167 HC |
To explore whether BDNF levels can differentiate between MDD and bipolar disorder in the first depressive episode |
At baseline, lower BDNF mRNA levels and plasma levels in BD and MDD patients compared to HC.
Lower BDNF levels in the BD group compared to the MDD group. The best model for predicting BD during a first depressive episode was a combination of BDNF mRNA levels with plasma BDNF levels. |
| 3 | Nassan et al. 2015, Washington [47] | Cross-sectional | 82 BD pediatric and adolescent patients 855 BD adult 764 HC |
Association of BDNF Val66Met SNP with EO-BD through a case–control candidate gene study | No significant evidence of association of the minor Met allele of Val66Met with BD. Significant evidence of an association between EO-BD and Val66Met. |
| 4 | Çinar et al. 2016, Turkey [45] | Longitudinal |
20 BD
20 HC |
To assess the BDNF mRNA expressions in BD patients and HC | Downregulation of BDNF mRNA in mania compared to HC. In remission, increased BNDF mRNA levels, but still lower than those of the controls. |
| 5 | Soeiro-De-Souza, 2012, Brazil and USA [46] | Cross-sectional | 66 BD (41 manic and 25 depressed patients) 78 HC |
To determine if the Val allele is associated with increased creativity in BD | Higher BWAS scores in manic patients with the Val allele (Met−). This relationship was not observed in depressed patients or HC. No association between BDNF Met allele status and cognitive function in any of the groups. |
BDNF: brain-derived neurotrophic factor; MDD: major depressive disorder; BD: bipolar disorder; EO-BD: early-onset bipolar disorder; HC: healthy controls; mRNA: messenger RNA; SNP: single-nucleotide polymorphism; Met: methionine; Val: valine; BWAS: Barron Welsh Art Scale; Val66Met: substitution of an amino acid valine with a methionine.