Riding the Range (of Genetics)

Abraham Lincoln's DNA and Other Adventures in Genetics By Philip R. Reilly New York: Cold Spring Laboratory Press (2000). 358 pp. $25.00“Ultimately, we will find and understand the genes that contribute to manic-depressive illness,” says Philip Reilly in his new book. Yet the group that Reilly says received “$2.5 million to find the culprit genes” (p. 110) recently concluded, “any underlying genetic etiology of BP [manic-depressive or bipolar affective] disorder is too complex to be resolved in genome scans with single-major locus assumptions and in linkage analyses involving fewer than many hundreds of multiplex families” (Friddle et al., Am. J. Hum. Genet. 66, 205–215, 2000). A few months ago, I searched PubMed for papers on genetics and bipolar affective disorder. I found that recent reports of failure to confirm previously reported genetic associations outnumber confirmations and reports of new associations by 19 to 12. Even if we eventually do find highly penetrant alleles that contribute to manic-depressive or other frequently occurring illnesses, they will predict only a very small proportion (generally less than 5%) of people who will develop the illness in question. Genes undoubtedly play a role in a larger proportion, but so many independently segregating alleles must be simultaneously present that identifying them will be like “finding a needle in a needle stack” (Weiss and Terwilliger, Nat. Genet. 26, 151–157, 2000). It also remains to be proven whether knowledge of susceptibility-conferring genotypes will improve treatment.With the search for genes for common complex diseases so problematic, it does not seem unreasonable to ask whether public funds should finance the search or, instead, support other approaches to preventing disease. This is not a question that Philip Reilly ponders. As his optimism about manic-depressive illness indicates, he is decidedly bullish about genetics, perhaps reflecting his current position as CEO of a biotechnology company.Reilly's book covers many more topics than the title suggests, each of them exuding enthusiasm for the role of genetics. The first section showcases the power of DNA analysis to solve historical but not momentous problems: whether Abraham Lincoln had Marfan syndrome, Toulouse-Lautrec pycnodysotosis, George III of England acute intermittent porphyria, and whether bones exhumed from a mass grave belonged to Tsar Nicholas II and his daughters. Only the last mystery has been solved (they did), but the technology is available to solve the others. The remaining sections, dealing with forensic uses of DNA, behavioral genetics, genetically modified organisms, genetic testing, gene therapy, cloning, frozen embryos, and eugenics, raise important issues that humankind faces as genetic technology expands. Reilly is masterful in fleshing out the “adventures” as he rides the range, making for pleasurable and informative reading.Reilly has had direct involvement with about half of the topics that he describes. As a lawyer, he reviewed amicus briefs maintaining that an 8-cell frozen embryo was not a child. As a physician, he encountered patients with Alzheimer's disease. As a medical geneticist and genetic counselor, he has counseled difficult cases. And, as a consumer with a special interest in genetics, he has been invited to sample genetically modified foods. He has been on a number of panels and committees, including one that considered whether Lincoln's DNA should be studied (it wasn't) and the National Academy of Sciences committee studying DNA forensics. His involvement personalizes the “adventures” and provides authenticity, but creates problems when he justifies his positions without fully exploring opposing viewpoints. He dismisses concerns about a universal DNA identity bank simply as the views of those who foresee “the rise of an Orwellian state” (p. 77). In discussing genetically modified plants and animals, he says, “the benefits of this technology far exceed the risks” (p. 160). He briefly notes that transgenes that serve as internal pesticides may escape to weeds which then overgrow food crops, adding that “researchers cannot design experiments that assess such risks.” Consequently, we will have to “make the most of experience“ (p. 165), he says. This “experience” could devastate the food supply. Reilly does not consider whether world hunger is a distribution rather than a supply problem and whether transgenic crops may serve to further concentrate wealth. Only in informing a woman that her brother had fragile X, which placed her daughters at risk for having affected sons, does he express doubt about whether he did the right thing: “Without thinking through the implications of my decision, I ordered a special chromosome [fragile X] test … If I had not ordered the blood test to make the diagnosis [in her brother] I never would have … upset the sister's world” (pp. 271–272).Reilly is on firmest footing in discussing uses of DNA in the criminal justice system. He tells us that all 50 states in the U.S. have enacted laws to create DNA felon databanks. In some states only felons convicted of violent crimes are included; in others all convicted felons. In the United Kingdom, “the law permits the police to construct a DNA identity profile of everyone arrested for crimes ranging from shoplifting to murder“ (p. 70, emphasis in original). Louisiana permits taking of a DNA sample at arrest, and the International Association of Police Chiefs will urge Congress to do likewise (p. 76). Reilly asks whether the specimens collected on every newborn for genetic-metabolic screening should be retained for forensic uses. Having such a collection with which to compare DNA from a crime scene could identify first-time perpetrators. Moreover, as Reilly points out, “In limiting DNA profiling to convicted felons we are constructing a bank whose membership will reflect current social prejudices” (p. 77), such as the greater probability that a black will be convicted of a particular offense than a white. Reilly's fear of extending databanks is that “[i]f we determine that certain genetic variants are much more common among convicted felons than among the general population, it is possible that some will argue that these are markers of predisposition to commit crimes” (p. 77). How are the courts to resolve such arguments? Surprisingly, Reilly is silent on how our judiciary decides the legitimacy of scientific claims, an issue that has undergone change as a result of the Supreme Court's ruling in Daubert v. Merrell Dow (509 US 579, 1993), which held that a federal trial judge must insure that scientific testimony or evidence is not only relevant but reliable based on substantiation of validity.When discussing genetic diseases, Reilly tends to exaggerate the significance of the association between the gene and the disease. For example, the risk of breast cancer in a woman who carries a harmful BRCA1 mutation is not “15 to 20 times higher than that of the average woman” (p. 227), but only 6 to 8 times higher. The apolipoprotein E4 polymorphism does not explain “at least half, and perhaps as much as three-quarters … of the risk for developing Alzheimer's disease …” (p. 241). Moreover, in black populations apoE4 does not increase the risk of Alzheimer's disease, raising the question of whether apoE4 is itself responsible. Tests for BRCA1 or apoE4, consequently, have lower clinical validity than Reilly implies.Sections describing genetic associations with violence, happiness, novelty seeking, homosexuality, and intelligence also reflect Reilly's optimism that a genetic basis for behavioral traits will be found. In some cases, he bases his argument on the high heritability found through twin studies, ignoring a number of problems with such studies (Harrap and Hopper, Lancet 357, 83–84, 2001). Moreover, knowing the heritability is not tantamount to knowing how many different gene loci are involved. As is the case with the common, complex diseases, the number of genes involved in any behavioral trait will be very large. Reilly maintains, “It is highly likely” that “(t)he revolution in molecular genetics will soon permit us to make a serious attempt at answering” the question of “why persons who score high [on IQ tests] are intelligent” (p. 140). A paragraph later he comes to his senses and comments, “If even as few as 100 genes control most of one's potential to do well on an IQ test, each is likely to make only a small contribution … It is extremely unlikely that [any scientist] … will ever be able to perform a large enough study to isolate these effects …” (p. 140). It is surprising, therefore, for Reilly to conclude the chapter by saying that the research journey on which scientists have embarked “will someday result in our learning how to genetically enhance intelligence” (p. 143).Nested within these adventures are educational nuggets that Reilly hopes will improve knowledge of genetics of the uninitiated reader. I have tried to put myself in the shoes of an interested but poorly informed reader and cannot conclude that I come out with a coherent picture of genetics. Nevertheless, few readers will be put off by the technical jargon, which is limited. They will come away recognizing the scope of issues affected by advances in genetics, although perhaps with more optimism about how this science will affect all our lives than is warranted.