APOE and Alzheimer disease: [50] In healthy ApoE-4 carriers, increased thickness has been associated with impaired selective attention [51] and, interestingly, neuropathological studies of healthy elderly subjects compared to asymptomatic AD subjects and patients with AD-MCI have shown the existence of a phase of hypertrophy of the neuronal cell bodies in preclinical AD that precedes the atrophy of these areas in symptomatic patients. [52] Similarly, patients with early Huntington’s disease present specific increased thickness in the ACC that progresses to neuronal atrophy in more advanced stages. [53].