Bloom syndrome - Affects a very large number of jews. It results in dwarfism. Bloom syndrome victims have a high-pitched voice. It is a cancer-prone genetic disorder that is inherited as an autosomal recessive disease. Its most remarkable feature is genetic instability in the form of increased frequencies of breaks and interchanges that occur either spontaneously or, in the laboratory, after treatment with various DNA-damaging agents. Those with the full-blown disease die by the age 16. The trait is carried by one out of every 120 jews. However, large numbers of jews have a lesser trait of the disease, in which jewish dwarfism is commonly seen and with their small bodies and disproportionately large sized heads, it may account for their troll like appearance. Jews like Madeleine Albright, comedian Jerry Stiller, and Menachem Begin have this appearance. In jewish communities such as in New York and Miami very short jews are seen waddling about. Examples of people who ostensibly have this disease trait are former Prime Minister Shamir at 5'1" tall and California Senator Barbara Boxer, who is under 5 feet tall. Leon Trotsky and many other jewish leaders in the Bolshevik revolution were very short as well.

Clinically, children with Bloom syndrome have small bodies, usually exhibit an erythematous (red skin produced by capillary congestion) "butterfly rash" that is sensitive to sunlight, excessive hyper- and hypo-pigmented skin lesions located anywhere on the body, and a high rate of bacterial infections due to immunodeficiency. These children are prone to cancer, chronic lung disease, and diabetes. Bloom syndrome is more common among Ashkenazi Jews than any other population.