MDK and early-onset autosomal dominant Alzheimer disease: Midkine, which has neuroprotective activity and neurite extension (Michikawa et al, 1993; Owada et al, 1999), expresses strongly in cerebral infarct (Yoshida et al, 1995) and Alzheimer's disease (Yasuhara et al, 1993; Salama et al, 2005).