Amish populations have higher incidences of particular conditions, including dwarfism,[90] Angelman syndrome,[91] and various metabolic disorders,[92] as well as an unusual distribution of blood types.[93] The Amish represent a collection of different demes or genetically closed communities.[94]
Although the Amish do not have higher incidence of genetic disorders than the general population,[95]
since almost all Amish descend from a few hundred 18th-century founders, some recessive conditions are more prevalent (an example of the founder effect).[96][97][98] Some of these disorders are rare or unique, and are serious enough to increase the mortality rate among Amish children. The Amish are aware of the advantages of exogamy, but for religious reasons, marry only within their communities.[99] The majority of Amish accepts these as Gottes Wille (God's will); they reject the use of preventive genetic tests prior to marriage and genetic testing of unborn children to discover genetic disorders. When a child is born with a disorder, it is accepted into the community and tasked with chores within their ability.[100] However, Amish are willing to participate in studies of genetic diseases.[98] Their extensive family histories are useful to researchers investigating diseases such as Alzheimer's, Parkinson's, and macular degeneration.
While the Amish are at an increased risk for some genetic disorders, researchers have found their tendency for clean living can lead to better health. Overall cancer rates in the Amish are reduced and tobacco-related cancers in Amish adults are 37% and non-tobacco-related cancers are 72% of the rate for Ohio adults. Even skin cancer rates are lower for Amish, even though many Amish make their living working outdoors where they are exposed to sunlight. They are typically covered and dressed by wearing wide-brimmed hats and long sleeves which protect their skin.[101]
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