Genetic disorders | Causes & Effects

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Genetic disorders can be caused by a mutation in one gene (monogenic disorder), by mutations in multiple genes (multifactorial inheritance disorder), by a combination of gene mutations and environmental factors, or by damage to chromosomes (changes in the number or structure of entire chromosomes, the structures that carry genes). Most genetic disorders are quite rare and affect one person in every several thousands or millions. Genetic disorders may be hereditary or non-hereditary, meaning that they are passed down from the parents' genes. However, in some genetic disorders, defects may be caused by new mutations, altered phenotype, or changes to the DNA. In such cases, the defect will only be passed down if it occurs in the germline. Genetic disorders can be monogenic, multifactoral, or chromosomal .there are Some types of recessive gene disorders confer an advantage in certain environments when only one copy of the gene is present Chromosomal disorder. A chromosomal disorder is a missing, extra, or irregular portion of chromosomal DNA. It can be from an atypical number of chromosomes or a structural abnormality in one or more chromosomes. An example of these disorders is Trisomy 21 (Down syndrome), in which there is an extra copy of chromosome 21. we are learning that nearly all diseases have a genetic component. Some diseases are caused by mutations that are inherited from the parents and are present in an individual at birth, like sickle cell disease. Other diseases are caused by acquired mutations in a gene or group of genes that occur during a person's life. Such mutations are not inherited from a parent, but occur either randomly or due to some environmental exposure (such as cigarette smoke). These include many cancers, as well as some forms of neurofibromatosis. Genes are sections or segments of DNA that are carried on the chromosomes and determine specific human characteristics, such as height or hair color. Because you have a pair of each chromosome, you have two copies of every gene. Some characteristics come from a single gene, whereas others come from gene combinations. Because every person has about 25,000 different genes, there is an almost endless number of possible combinations! Researchers have identified more than 4,000 diseases that are caused by mutations. But having a genetic mutation that may cause a disease or condition doesn't always mean that a person will actually develop that disease or condition.On average, people probably carry from 5 to 10 genes with mutations in each of their cells. Problems happen when the particular gene is dominant or when a mutation is present in both copies of a recessive gene pair. Problems can also happen when several variant genes interact with each other — or with the environment — to increase susceptibility to diseases. If a person has a change in a dominant gene that is associated with a particular condition, he or she will usually have features of that condition. And, each of the person's children will have a 1 in 2 (50%) chance of inheriting the gene and developing the same features. Diseases and conditions caused by a dominant gene include achondroplasia (pronounced: ay-kon-druh-PLAY-zhuh, a form of dwarfism), Marfan syndrome (a connective tissue disorder), and Huntington disease (a degenerative disease of the nervous system). John George Associate Editor Journal of Genetic Disorders and Genetic Medicine Email: geneticmed@molecularbiol.com