In this review, we will focus on the signaling regulatory functions of <i>CTNND2</i> and its encoded protein δ-catenin in neuro-related diseases and cancers, and discuss the limitations of previous investigative studies and the challenges of the future researches on <i>CTNND2</i> and δ-catenin signaling. The gene discussed is CTNND2; the disease is cancer.