Genetic Disease I History and Mechanisms

Larry Leon Mai

A genetic disease may be defined as any condition caused or influenced by a malfunctioning gene or cytogenetic (chromosome) error that affects an organism's capacity for adaptation. Excepting lethal defects and sterility, genetic diseases display certain familial modes of inheritance and exhibit morbidity and mortality patterns that may compromise direct fitness. Genetic diseases have been called "inborn errors of metabolism," molecular defects, hereditary diseases, and familial diseases (Mai, Young Owl, & Kersting, 2004). Synonyms for

"disease" in this context include anomaly, condition, morbid effect or defect, deficiency, disorder, and syndrome.

Some sources restrict discussions of genetic disease to defects of single genes; others include polygenic disorders and the cytogenetic defects as well (Habener & Williams, 2001; King, Rotter, & Morulsky, 1992).1 This entry touches on all three manifestations of mutation.

Worldwide, more than half of all conceptions, and about 7% of all live-born children, are affected by some form of genetic disease.

Many folk taxonomies of "disease" classify affected individuals with due consideration to exceptional pheno-typic signs (including non-visual signals), whether self-reported or externally diagnosed (Atran, 1998). Western nosology2 also considers phenotypic signs and manifestations, but differs significantly from folk medical systems in the ascription of meanings to those signs—to the etiologies, or causes of phenotypic morbidity (Marks, 2001, pp. 62-64; McKee, 1987). As Western medicine diverged in recent centuries from its folk-based roots, its etiologies incorporated at first histological, then cellular, and finally, sub-cellular and molecular aspects. Each of these diagnostic levels has been progressively dependent upon an evolving and sometimes invasive technology. Consequently, the Western process of clinical diagnosis has become, in large part, a taxonomy of inferred mechanisms and nanomechanisms appended to classic pheno-typic descriptions.

Among the most esoteric and counter-intuitive aspects of Western medical subsystems is the ascription of "genetic" causes to phenotypic morbidity. A genetic etiology has three facets: the exceptional phenotype, a familial mode of transmission (when reproduction is possible), and a cryptic mode of defect (mutation). Historically, the realization of these facets proceeded in that order, as well. Although most traditional medical systems acknowledge abnormal phenotypes, exact knowledge of transmission modes is sometimes problematic, and full knowledge of the mechanisms of mutation is for the most part recent and specifically Western.

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