Book Review
Genetic Instabilities and Hereditary Neurological Diseases
N Engl J Med 1999; 341:1554-1555November 11, 1999
- Article
Genetic Instabilities and Hereditary Neurological Diseases
Edited by Robert D. Wells and Stephen T. Warren, with Marion Sarmiento. 829 pp., illustrated. San Diego, Calif., Academic Press, 1998. $159.95. ISBN: 0-12-742935-2Elucidation of the structure of DNA by J.D. Watson and Francis Crick was exciting because of its potential to explain the function of this molecule. I find this book, which examines the expansion of oligonucleotide triplet-repeat sequences in patients with neurologic disease, similarly engrossing, since it affords major insights into molecular pathogenesis. The disruption such mutations cause within a coding or noncoding region of a gene can, like more commonly recognized mutations, affect the gene's performance, but abnormal triplet-repeat sequences have additional consequences.
For instance, the mechanism of genetic anticipation and increasing penetrance, whereby disease develops in a more severe form and at an earlier age in offspring than in their parents, became apparent with the finding that the triplet-repeat sequence is amplified in successive generations, leading to a successively larger and more disruptive mutation. Moreover, the increasing size of the triplet-repeat sequence causes interference in the regulation and transcription of neighboring genes, which are moved apart by the expanding nucleic acid polymer, or results in a progressively more abnormal protein in the case of a mutation in a coding region. In fact, the abnormal glutamine polymer in a protein encoded by a triplet-repeat sequence of CAG aggregates and thereby has serious consequences, not unlike the damage caused by amyloid and prion aggregates.
About half of this approximately 2-kg book details the clinical and molecular aspects of 12 disorders that have been confirmed to result from abnormal triplet-repeat sequences (including Huntington's disease, myotonic dystrophy, Friedreich's ataxia, and the fragile X syndrome), diseases that are likely to result from this type of mutation (including both psychiatric and neurologic conditions), and animal models of many of these mutations. Eight of the known mutations are (CAG)n oligonucleotide repeats (where n is the number of repetitions), and single examples of (CTG)n, (CGG)n, (GAA)n, and (GCC)n repeats have been identified thus far. The balance of the book addresses the techniques used to detect and study unstable triplet-repeat sequences; the biophysical, structural, and functional aspects of triplet-repeat sequences; the resulting abnormal protein products; and other nontriplet dynamic mutations, including the enlarged dodecamer repeat.
What makes the content of this book riveting is that, in addition to the inherent fascination of the story of triplet-repeat sequences, all the authors have combined their outstanding, scholarly presentations with a passion and an enthusiasm that are hard to ignore. As details of pathogenesis are laid out for us, many options for the development of logical treatments appear on the horizon, adding to the excitement. Furthermore, I have never seen a book with such up-to-date information from so many contributors. The text is filled with new data and breaking reports of unpublished findings, nearly all of which I was unable to find in current-literature searches at the time of my reading. This overall synthesis of current knowledge on unstable triplet-repeat sequences is clearly as good as it gets.
Who may benefit from this book? Although it is very well written and is readable, the breadth and detail it covers may put off those who want a distilled and brief outline of the field. Those who desire the bottom line will be satisfied with the excellent first chapter, which summarizes the field, and the short concluding chapter, which points to many challenges for the immediate future. However, I think this story is so compelling and so well told that all who are interested in the diagnosis, pathogenesis, and future treatment of hereditary brain diseases must read this masterpiece.
Michael Harrington, M.B., Ch.B.
Huntington Medical Research Institutes, Pasadena, CA 91101
