Genetic defects: genetic health.
A disorder or disease caused by a damaging gene variation that may be inherited.
An abnormal trait or disease that results from mistakes in an individual’s “genetic blueprint,” such as a problem in the DNA coding of the genes or errors in duplication of the chromosomes. The defective gene may have been received from one or both parents, as part of the individual’s genetic inheritance, or it may stem from a mutation in the genetic material in the sperm or egg (ovum) that joined at conception to form the new individual.
Medical conditions caused by errors in genetic material. Some genetic disorders cause medical problems that are apparent at birth, while others do not show up until later in life. Some genetic disorders, such as cystic fibrosis, can be so severe that they ultimately cause death, while others, like color blindness, produce mild symptoms. Genetic disorders can be rare or common. They can be caused by an error in the DNA of a single gene; by abnormalities of entire chromosomes; by combinations of genes and environmental factors, such as diet or chemical exposure; or by mutations in mitochondria (self-reproducing parts of cells).
These are caused when there are mutations or other abnormalities which disrupt the code of a gene or set of genes. These are divided into autosomal (one of the 44 chromosomes which are not sex-linked), dominant, autosomal recessive, sex-linked and polygenic disorders.
A genetic disorder refers to any condition caused entirely or partially by one or more anomalies in an individual’s DNA. Such disorders may be congenital, meaning they are present at birth, or they might manifest later in life. Many are familial, occurring among multiple people in the same family. Nonetheless, a child may be born with a genetic disorder even when there’s no prior family history of it.
A genetic disorder can manifest in two distinct ways: it can be inherited from one or both parents who possess a defect in their own genetic material, or it can arise from a mutation that happens during the creation of the egg or sperm cell.
Genetic disorders are categorized broadly into three types: chromosomal abnormalities, single gene defects, and multifactorial defects. Chromosomal abnormalities are when a child possesses an unusual number of whole chromosomes, or additional or lacking parts of chromosomes, as seen in Down’s syndrome. Single gene defects are rare and result from one abnormal gene or pair of genes. Multifactorial disorders are believed to arise from the combined effects of several genes and environmental factors.
Single gene defects primarily take two forms. Sex-linked disorders occur when the faulty gene is located on one of the sex chromosomes, typically the X chromosome. In contrast, autosomal disorders arise when the defective gene is found on any of the remaining 44 chromosomes. These disorders are further classified into autosomal dominant and autosomal recessive disorders.
Another infrequent category of single-gene abnormalities concerns the mitochondrial DNA, which exists outside the cell nuclei.
The most prevalent form of sex-linked disorder is X-linked recessive disorders, which result from a faulty gene located on an X chromosome. Examples of this type include haemophilia and color blindness.
Women have two X chromosomes; men have only one, inherited from their mothers. When a woman inherits one defective gene, its effect is masked by the normal gene on her other X chromosome and she has no abnormality. She is, however, capable of passing the gene on to her children, and is called a carrier. On average, carriers transmit the defective gene to half their sons, who are affected, and to half their daughters, who become carriers in turn. When a
male inherits the defective gene from his mother, he has no normal gene on a second X chromosome to mask it, so he displays the abnormality. Affected males therefore greatly outnumber affected females. The males pass the defective gene to none of their sons but to all of their daughters, who become carriers.
Under these circumstances, the faulty gene exerts dominance over the corresponding normal gene, meaning that just one copy is sufficient to cause an abnormality. Individuals with an autosomal dominant disorder carry both a normal and a defective copy of the affected gene, making them heterozygotes. Affected individuals have a 50 percent likelihood of passing the defective gene to their offspring.
The gene responsible for causing an autosomal recessive disorder exhibits recessiveness when compared to the normal gene. As a result, two faulty copies of the gene must be present to trigger an abnormality. Individuals who have the disorder carry two identical defective copies of the gene and are referred to as homozygotes. In the majority of cases, both parents of an affected individual are heterozygotes, meaning they carry one copy of the defective gene and one copy of the normal gene.
In uncommon instances, diseases can arise from defects in a particular region of mitochondrial DNA. These disorders encompass certain myopathies (muscle disorders), neuropathies (nerve disorders), as well as certain cases of retinal degeneration and deafness. It’s important to note that these disorders are always inherited from the mother since sperm cells contain very few or no mitochondria.
Various disorders, such as asthma, diabetes mellitus, and many types of hyperlipidemia, are believed to stem from the combined impact of multiple faulty genes along with environmental influences. Unlike chromosomal abnormalities or single gene defects, the inheritance pattern in these disorders is more intricate and less straightforward.