 As in many fields, debates over reductionism versus holism are rife in medicine both with reference to medical research and practice, and the terms often are used rather loosely to mean a range of things (for a related discussion see entry on   reductionism in biology).  In the broadest terms, reductionistic approaches to disease look for fundamental mechanisms or processes that are the underlying causes of that disease. In recent years in light of large-scale genomic sequencing initiatives notably the Human Genome Project, there has been considerable emphasis on reducing diseases to the genetic or molecular level. Those who advocate more holistic approaches note that reductionism leaves out important information based on the patient’s experiences of the disease at the phenotypic level, and such information is critical to pursuit of effective treatments. Many diseases typically viewed as “genetic” have proven to be extremely difficult in practice to reduce to unified disease entities with singular (or simple) genetic causes, including mental illnesses (Harris and Schaffner 1992), cystic fibrosis (Ankeny 2002), and Alzheimer’s disease (Dekkers and Rikkert 2008). As Catherine Dekeuwer (2015) notes, given that there probably is genetic variation in susceptibility to virtually all diseases, there is no clear demarcation between genetic diseases and diseases for which there are genetic risk factors; hence she argues that our tendency to focus on genetic determinants of disease may reinforce folk notions of the geneticization of both people and of human behavior.