Founder effects occur when a small number of individuals from a larger population establish a new population. In this illustration, the original population is on the left with three possible founder populations on the right. Two of the three founder populations are genetically distinct from the original population. Ashkenazi Jews have a high incidence of<unk><unk>  and other lipid storage diseases. In the United States, about 1 in 27 to 1 in 30 Ashkenazi Jews is a recessive carrier. The disease incidence is about 1 in every 3,500 newborn among Ashkenazi Jews. French Canadians and the Cajun community of Louisiana have an occurrence similar to the Ashkenazi Jews. Irish Americans have a 1 in 50 chance of being a carrier. In the general population, the incidence of carriers as heterozygotes is about 1 in 300. The incidence is approximately 1 in 320,000 newborns in the general population in the United States. Three general classes of theories have been proposed to explain the high frequency of<unk><unk>  carriers in the Ashkenazi Jewish population: * Heterozygote advantage. When applied to a particular allele, this theory posits that mutation carriers have a selective advantage, perhaps in a particular environment. * Reproductive compensation. Parents who lose a child because of disease tend to "compensate" by having additional children following the loss. This phenomenon may maintain and possibly even increase the incidence of autosomal recessive disease. * Founder effect. This hypothesis states that the high incidence of the 1278insTATC chromosomes is the result of an elevated allele frequency that existed by chance in an early founder population.<unk>  was one of the first genetic disorders for which epidemiology was studied using molecular data. Studies of<unk><unk>  mutations using new molecular techniques such as linkage disequilibrium and coalescence analysis have brought an emerging consensus among researchers supporting the founder effect theory.
Tay–Sachs disease
Sandhoff disease
Fox–Fordyce disease
Leigh syndrome
Bietti's crystalline dystrophy
Neuronal ceroid lipofuscinosis
Akureyri disease
Dejerine–Sottas disease