BDNF and major depressive disorder: The role of single nucleotide polymorphisms (SNP), such as the Val66Met (e.g., rs6265), a functional SNP within the first exon of BDNF affecting ketamine response, was studied in patients with MDD: those with the Val/Val BDNF allele at rs6265 are more likely to exhibit increased antidepressant response to ketamine than Met carriers [145].