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Genetic Disorders Definition
Genetic Disorders is a collective classification for syndromes, diseases, and congenital anomalies that result from alterations of the genes and chromosomes.There are four general categories of genetic disorders, each relating to the way in which the alterations manifest.
The normal human GENOME contains 23 paired chromosomes. CHROMOSOMAL DISORDERS occur when there are disruptions in these pairings in which there is an extra CHROMOSOME (trisomy) or a missing chromosome (monosomy). Chromosomal disorders also occur when large segments of a chromosome are damaged or missing (deletion syndromes). Less often, a broken segment of a chromosome attaches itself to another chromosome (TRANSLOCATION). Common chromosomal disorders include DOWN SYNDROME, EDWARDS SYNDROME, PATAU’S SYNDROME, TURNER SYNDROME, and KLINEFELTER’S SYNDROME.
Each GENE encodes, or directs, a specific action within the body. Single-gene disorders, in which a MUTATION of a gene or set of genes causes malfunctions of the proteins that carry out the gene’s instructions, cause conditions of faulty encoding, either because the gene’s protein messenger is missing or incomplete. The disorders that result often become more severe over time as the malfunction continues to repeat itself. CYSTIC FIBROSIS, SICKLE CELL DISEASE, Duchenne’s MUSCULAR DYSTROPHY, HUNTINGTON’S DISEASE, and MARFAN SYNDROME are single-gene disorders.
Researchers suspect many health conditions arise as a result of an interplay between genetic and environmental factors. Geneticists call such conditions multifactorial disorders because it appears a certain combination of events must take place for disease to result; doctors may refer to them as conditions of GENETIC PREDISPOSITION. These are the conditions that tend to run in families; some family members develop them and others do not. Health conditions in which genetics, lifestyle, and other variables participate in the development of disease are numerous. Some of those that are common include CORONARY ARTERY DISEASE (CAD), HYPERTENSION (high BLOOD PRESSURE), CANCER, DIABETES, GALLBLADDER DISEASE, and NEPHROLITHIASIS (kidney stones), and numerous other conditions.
Mitochondria are self-replicating structures within a cell (called organelles) that carry out the metabolic functions of the cell. Mitochondria have their own DNA that directs their specific functions, and have multiple copies; MITOCHONDRIAL DNA (MTDNA) is different from the cell’s nuclear DNA. MITOCHONDRIAL DISORDERS, which are the rarest of the genetic disorders, occur when the genes that encode mitochondrial activity contain mutations or when there are defects in the mtDNA. Mitochondrial disorders tend to vary widely among individuals, causing different symptoms because they affect different, and usually multiple, organs or structures. Doctors define the disorder as a complex of symptoms. Some forms of ENCEPHALOPATHY, MYOPATHY, and CARDIOMYOPATHY are mitochondrial disorders.