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A disease caused by any abnormality in a person’s genes or chromosomes is called a genetic disorder. Several diseases have a genetic side to them. Some genetic disorders are inherited. Since you inherit genes from your parents, you may also inherit any abnormality in the gene. That is one of the tenets of genetics, the branch of biology associated with the study of genes and their effects. A gene that has undergone a mutation (alteration) is passed down through a family and the genetic disorder caused by the mutated gene can affect children of all the subsequent generations. These mutations, or alterations, in genes can occur due to exposure to environmental toxins or may occur randomly. Genetic disorders are also caused by abnormalities in the structure and function of chromosomes. It is imperative to note that not all genetic disorders are inherited. Some, like Down’s syndrome, occur as isolated random incidents. Genetic disorders account for a large number of diseases, and can present in various ways. The most widely known genetic disorders are Down’s syndrome, Klinefelter’s syndrome, sickle cell anemia and spina bifida. Genetic disorders can often be lethal or may sometimes cause conditions that need a significant medical attention. More than 6000 genetic disorders have been identified till date. Genetic Disorders can be classified as * Single gene disorders * Complex disease * Chromosomal disorders Single gene disorders occur because of one defective gene. These disorders are uncommon and the biology behind them is not fully understood. Examples of this type of genetic disorder include muscular dystrophy and cystic fibrosis. Complex disease is the most common type of genetic disorder. In these disorders, gene mutation does not cause the disease, just increases the predisposition to the disease. Heart disease, obesity and Alzheimer’s disease are examples of complex disease. Chromosomal disorders occur because of abnormalities in the structure or number of chromosomes. Down’s syndrome and Klinefelters syndrome are prime examples of these disorders. Down’s syndrome, also referred to as Trisomy 21, is a genetic disorder caused by the presence of an extra 21st chromosome. The effect of the extra 21st chromosome varies greatly, depending on whether the extra strand is present is full or parts, genetic history, and pure chance. Down’s syndrome is characterized by some abnormality of cognitive ability, physical growth, and facial appearance. Some of the common physical features of a person with Down’s Syndrome include a single transverse palmar crease, instead of two, an almond shape to the eyes, shorter limbs, poor muscle tone, a larger than normal space between the big and second toes, and a protruding tongue. Individuals with Down’s syndrome also have specific health concerns such as a higher risk for congenital heart defects, recurrent ear infections, and thyroid dysfunctions. Klinefelter’s syndrome is caused by the presence of an extra X sex chromosome. The main result is the presence of small testes and reduced fertility. Other physical and behavioral problems are common, though the severity varies. It is the second most common extra chromosomal disorder. The biology behind genes and chromosomes and patterns of inheritance is yet to be completely deciphered. Genetics throws up interesting mysteries every now and then.
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George kakaris is a Master of Science in Applied Genetics He studied biology in Salonica, Greece and is really interested in Genetic Diseases and especially in Down Syndrome and Klinefelter Syndrome
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