Plenary Session II: Genetic Diversity and Epidemiology

✍ Scribed by Curry, Cynthia J.; Stevenson, Roger E.; Aughton, David; Byrne, Janice; Carey, John C.; Cassidy, Suzanne; Cunniff, Christopher; Graham, John M.; Jones, Marilyn C.; Kaback, Michael M.; Moeschler, John; Schaefer, G. Bradley; Schwartz, Stuart; Tarleton, Jack; Opitz, John

• Publisher: John Wiley and Sons
• Year: 1997
• Tongue: English
• Weight: 32 KB
• Volume: 74
• Category: Article
• ISSN: 0148-7299
• DOI: 10.1002/(sici)1096-8628(19971121)74:6<578::aid-ajmg3>3.0.co;2-g

✦ Synopsis

Neuropsychiatric disorders appear to be present in all parts of the world. Although the epidemiology in many parts of the world may be based on older or different diagnostic criteria, the general opinion is that the major disorders, such as schizophrenia and bipolar affective disorder, occur with frequencies that only vary slightly among populations. This near uniformity across diverse cultures is usually taken as evidence that there are significant genetic components to the etiologies of these disorders. However, how likely is it that the genetic factors predisposing to each disorder are the same ones at the same frequencies in all populations? With modern molecular genetic techniques it is now possible to identify and study variation in the DNA sequences among individuals. DNA studies of humans, mostly done within the past decade, have begun to provide new insights into how the human genome has evolved and how variation within that genome is distributed among individuals and around the world. This growing understanding of human genetic diversity emphasizes the point that, if we are truly to understand the causes of neuropsychiatric disorders in humans, we must study all humankind. We need to understand not only the current pattern of genetic diversity but also the evolutionary history that produced that diversity. For example, we need to understand the evolutionary histories of allelic variants for normal genetic markers at candidate loci since, if a locus really has genetic variation influencing susceptibility to a complex trait, that variation also has an evolutionary history and it will be tied to the history of the adjacent normal DNA sequence variation. We now have initial results for a few loci, some of great neuropsychiatric interest, such as DRD2 and DRD4. Our understanding of human population histories also relates to how readily a finding in one ethnic group or geographical region will generalize to other people: only some generalizations are possible and causes common in one group may not be the common causes of the same apparent disorder in another group. METHODS IN OUR MADNESS: TWINS, EVERY WHICH WAY. Irving I. Gottesman. University of Virginia.

Sir Francis Galton's intuitive ideas (1875) about the use of twins to study behavior were not implemented as a scientific method until 1924 by Siemens in Germany and by Merriman in the United States. The so-called classical method of comparing the concordance rates for identical and fraternal twins has undergone numberous transformations and evolutions so that it can be used as a first line strategy for understanding all the components in the liability toward developing such complex, non-mendelian disorders as schizophrenia and bipolar disorder. Illustrations of the application of the uses of twins concordant and discordant for mental disorders to understand pathogenesis, to identify triggers or protective factors for genetic vulnerabilities, and to identify ''spectrum'' conditions that