In a sample of 40 AD cases and controls, Laske et al. [12] found that serum brain derived neurotrophic factor (BDNF) levels varied according to AD severity, suggesting BDNF as a potential biomarker for AD, though we failed to cross-validate these findings in a sample of 198 AD cases and controls from the Texas Alzheimer's Research Consortium (TARC) cohort [13]. Here, BDNF is linked to Alzheimer disease.