In addition, clinical studies imply that BDNF can serve as both a biomarker and therapeutic target in AD, and there are propositions for using composite biomarkers, such as dual-specificity tyrosine phosphorylation-regulated kinase 1A (DYRK1A), homocysteine and BDNF, to facilitate the early diagnosis of AD [78]. This evidence concerns the gene BDNF and Alzheimer disease.