Jewish Genetic Disorders: A Layman's Guide (review)

This book provides precisely what it promises. Every genetic disorder that is present at a high rate in any subgroup of Jews (for example, those from Libya) is described in a clear and concise manner. A glossary provides help with unfamiliar terms. And there is a detailed index. Furthermore, the disorders are grouped together by symptoms so a disease might be located even if its name is not familiar.

The book opens with a discussion of diseases in general and the distinction between inherited disorders such as Tay Sachs and acquired ones like AIDS. Each “ethnic group” seems to have certain diseases in excess. While to some, this observation may smack of racism, in fact ignorance is dangerous. Knowing that your group is subject to a particular ailment, genetic or otherwise, makes it more likely that the problem can be detected at an early stage. For example, Ashkenazic Jews should be particularly diligent in being screened for colon cancer.

Beyond that, it is now possible to screen for carriers of many genetic diseases. By knowing what diseases are common in each ethnic group or sub-group it is possible to use these tests in the most cost-effective manner. The author discusses the available screening tests, how they are performed, and who should take them. He also describes the striking new technique of pre-implantation diagnosis whereby the embryo can be tested genetically and discarded if it is carrying the gene of interest. This procedure can assure a couple that their child will be free of disease without the physical and psychological trauma of an abortion.

Genetics is a vast and complicated topic, yet Dr. Abel makes it all seem simple and accessible. He even illustrates how it can be used to trace the historical migrations of the Jews across Europe and the Middle East. From the standpoint of human genetics, however, the key question is why are some nasty diseases like cystic fibrosis so common overall and why are otherwise rare diseases like Tay-Sachs so frequent in Jews of Ashkenazic origin. One reason is luck, otherwise known as the founder effect. By chance a rare deleterious gene is found in the group that initiated a new settlement. If the group prospers, for whatever reason, the bad gene will “prosper” with it.

More interesting is what Dr. Abel calls the “Faustian bargain.” Natural selection, although slow, is very effective. That is why most deleterious genes are present only at very low levels in the populations. Usually, a person who has inherited a defective gene from one parent and a normal one from another is perfectly normal and the gene is called recessive. But in some rare instances, the carrier (or heterozygote) is actually at a selective advantage. This would keep the defective gene in the population at a high level. The best understood example of this is sickle cell anemia. A double dose of the gene is often fatal, while a combination of one normal and one sickle cell gene protects the carrier from malaria. Similarly, the cystic fibrosis gene seems to protect the carrier from cholera and typhoid fever and the gene for Tay-Sachs protects the carrier from tuberculosis.

The heart of the book is a discussion of individual diseases. Not only are the well known “Jewish” diseases considered, but others that are less common or less serious and hence less prominent. These include Familial Mediterranean Fever, which turns out to be prevelent in Ashkenazic as well as Sephardic Jews, and Cystinuria, which is only common among Libyan Jews.

The discussion of each disease includes a history of its discovery, a review of its symptoms and treatment (which sometimes can be very effective), and its frequency in the population. In most cases a definitive diagnosis will require identifying the mutated gene at a cost of $100–$300. Most important, there is a listing of support groups, centers specializing in the disease, and for those who are interested, recent papers and books dealing with...