Mtap4 encodes isoforms of MAP4 with differing microtubule-stabilization properties (Hasan et al., 2006) that have been proposed to regulate the dynamic behaviors of extending neurites (Hasan et al., 2006), structures lost or altered in the earliest stages of Alzheimer's disease (Knobloch and Mansuy, 2008). Here, MAP4 is linked to early-onset autosomal dominant Alzheimer disease.