ATP7B and early-onset autosomal dominant Alzheimer disease: The paradigm recently proposed of a shift from the “common disease—common variant hypothesis “to a “common disease—multiple rare variants hypothesis” may suitably fit to the ATP7B gene association with Alzheimer's disease, since the gene is highly polymorphic but at the same time harbors rare mutations, that in homozygous or heterozygous compounds trait are causative of Wilson's disease (Squitti R. personal communication).