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Because Tay – Sachs disease was one of the first autosomal recessive genetic disorders for which there was an enzyme assay test ( prior to polymerase chain reaction testing methods ), it was intensely studied as a model for all such diseases, and researchers sought evidence of a selective process.
A continuing controversy is whether heterozygotes ( carriers ) have or had a selective advantage.
Neil Risch writes: " The anomalous presence of four different lysosomal storage disorders in the Ashkenazi Jewish population has been the source of long-standing controversy.
Many have argued that the low likelihood of four such diseases — particularly when four are involved in the storage of glycosphingolipids — must reflect past selective advantage for heterozygous carriers of these conditions.

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