Although we did not pursue this observation further, it is worthy to note that a serine/threonine kinase PKN (also known as protein kinase C-related kinase 1), which is involved in the pathogenesis of Alzheimer's disease and amyotrophic lateral sclerosis,33, 34 interacts with and phosphorylates cdr2.13 Here, MARK2 is linked to early-onset autosomal dominant Alzheimer disease.