The CC genotype of transforming growth factor-β1 increases the risk of late-onset Alzheimer's disease and is associated with AD-related depression.

Transforming growth factor-β1 (TGF-β1) is a neurotrophic factor that exerts neuroprotective effects against β-amyloid-induced neurodegeneration. Recently, a specific impairment of the TGF-β1 signaling pathway has been demonstrated in Alzheimer's disease (AD) brain. TGF-β1 is also involved in the pathogenesis of depressive disorders, which may occur in 30–40% of AD patients. The TGF-β1 gene contains single nucleotide polymorphisms (SNPs) at codon +10 (T/C) and +25 (G/C), which are known to influence the level of expression of TGF-β1.