However, these drugs only showed modest effects on AD patients. It was only after the development of genetics and molecular biology studies on AD that mutations in the APP gene as well as inheritance of the ε4 allele of apolipoprotein E were recognized as contributory factors to the pathogenesis of AD. In spite of this, most cases of AD are sporadic, with dominantly inherited forms accounting for less than 1% of AD patients. Thus, both environmental factors and epigenetic changes may present a critical issue for the treatment of AD.