However, there is also evidence that at early stages of HD, TrkB signaling is altered due to an indirect effect of p75 neurotrophic receptor (p75NTR) activity, indicating that signaling defects may precede aberrant secretion of BDNF, a ligand of both TrkB and p75NTR (Plotkin et al., 2014). This evidence concerns the gene NTRK2 and Huntington disease.