In various studies on multiple distinct ethnic groups and several different data sets performed over the last two decades, it has been shown that the epsilon 4 (E4 or ε4) variant of the apolipoprotein E (APOE) gene is associated with an increased risk for both sporadic and familial forms of Alzheimer disease (AD). The gene discussed is APOE; the disease is early-onset autosomal dominant Alzheimer disease.