Dr. Swarkar Sharma,
Have ever wondered why humans give birth to humans, elephants to elephants, fish to fish and it remains the same for all the living beings. Nature works here in a peculiar way and answer to this lies in a molecule called Deoxyribonucleic Acid (DNA). DNA contains biological instructions to make each species unique and along with the instructions it contains is inherited to next generation. This biological information is encoded in fragments of DNA called Genes. There are approximately 20,000-25,000 Genes in humans. These individually or in combinations, including interactions with environment, take care of composition and all the functions of Human body. Each Gene has two copies and Mother and Father contribute equally, one copy each. In this way, transmission of characters from parents to offsprings is controlled (known as heredity). Genetics is a field of biology that helps us understand these principles and mechanisms.
During course of inheritance, from one generation to another, many a times some changes arise in DNA, which are called mutation or variations and are inherited to the next generation. These variations can be neutral or may have negative or positive impact as they may affect function of a Gene. When a positive effect, it can be beneficial by helping in adaptation to environment and better survival. However, if negative impact, may result in a disease condition: the scenario in Genetic Diseases. As there are two copies of each Gene present in an individual, mutations effect differentially in causation of diseases. In an individual, if one copy of the gene inherited has mutation, the disease may show up but with a milder effect or no effect. However, if both the inherited copies of Gene are with mutation the situation turns severe and many a times lethal and are called recessive genetic disorders. Because recessive disorders have severe implications and are lethal these diseases are very rare in incidences and most of the times are restricted to closely related individuals and families. Yet, all the rare disorders together affect more individuals than common diseases like Cancer and Diabetes. So, it is important to be aware and understand these disorders. At present, about thousands of different types of rare disorders are known, some of which are Cystic Fibrosis, Sickle Cell Disease, Fragile X Syndrome, Muscular Dystrophy, or Huntington disease. Rare genetic disorders can have detrimental effects on any part of the body. These may appear in an individual randomly but rarely, inheriting two different mutations in same Gene by chance. However, scientific evidences exist suggesting such disorders are found more frequently among those families that follow a trend of performing repetitive consanguineous marriages, that is, marriages between and restricted to close blood-relatives. Closer the relationship, higher is the possibility of inheritance of
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