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A genetic disorder, or genetic disease is a disease caused, at least in part, by the genes of the person with the disease. There are a number of possible causes for genetic defects: A disease is any abnormal condition of the body or mind that causes discomfort, dysfunction, or distress to the person affected or those in contact with the person. ...
- They may be caused by an unwelcome mutation, as are most cancers.
- There are genetic disorders caused by the accidental duplication of a chromosome, as in Down syndrome and Klinefelter's syndrome, or repeated duplication of part of a chromosome as in Fragile X syndrome.
- The defective genes are often inherited from the person's parents. In this case, the genetic disorder is known as a hereditary disease. This can often happen unexpectedly when two healthy carriers of a defective recessive gene reproduce, but can also happen when the defective gene is dominant.
| Contents | 1.1 Transmission of single gene disorders
This article is about mutation in biology, for other meanings see: mutation (disambiguation). ...
When normal cells are damaged or old they undergo apoptosis; cancer cells, however, avoid apoptosis. ...
Figure 1: Chromosome. ...
XXY karyotype Klinefelters syndrome is a condition caused by a chromosome abnormality in males (specifically, a nondisjunction); sufferers have a pair of X sex chromosomes instead of just one. ...
Fragile X Syndrome is the most common inherited cause of mental impairment, and the most common known cause of autism. ...
In genetics, the term recessive gene refers to an allele that causes a phenotype (visible or detectable characteristic) that is only seen in a homozygous genotype (an organism that has two copies of the same allele). ...
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Single gene disorders
A number of genetic disorders are due to the change of a single gene, resulting in an enzyme or other protein not being produced or having altered functionality, they are called monogenic disorders. The change can be trivial and relatively harmless in its effects, such as color blindness, or lethal such as Tay-Sachs. Other disorders, though harmful to those afflicted with them, appear to offer some advantage to carriers; as in carriers of sickle cell anemia and thalassemia appearing to have enhanced resistance to malaria. Several hereditary diseases are sex-linked, meaning that they afflict one sex much more common than the other because the mutation is located on the X (or, rarely, on the Y) chromosome. This stylistic schematic diagram shows a gene in relation to the double helix structure of DNA and to a chromosome (right). ...
Neuraminidase ribbon diagram An enzyme (in Greek en = in and zyme = leaven) is a protein, or protein complex, that catalyzes a chemical reaction and also controls the 3D orientation of the catalyzed substrates. ...
A representation of the 3D structure of myoglobin, showing coloured alpha helices. ...
In genetics, monogenic genetic disorders are hereditary diseases that result from abnormalities in one (mono) gene. ...
Color blindness in humans is the inability to perceive differences between some or all colors that other people can distinguish. ...
Tay-Sachs disease is a fatal genetic disorder, inherited in an autosommal recessive pattern, in which harmful quantities of a fatty substance called ganglioside GM2 accumulate in the nerve cells in the brain. ...
Sickle-shaped red blood cells Sickle cell anemia (American English), sickle cell anaemia (British English) or sickle cell disease is a genetic disease in which red blood cells may change shape under certain circumstances. ...
Thalassemia (American English) (or Thalassaemia in British English) is an inherited disease of the red blood cells, classified as a hemoglobinopathy. ...
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Sex-linked genes are those carried on the mammalian X chromosome but not the Y chromosome. ...
Transmission of single gene disorders Where genetic disorders are the result of a single mutated gene they can be passed on to subsequent generations in the following ways, however genomic imprinting and uniparental disomy may affect inheritance paterns. Imprinting is the suppressing (or silencing) of certain genes on chromosomes, depending on which parent they were received from. ...
Uniparental disomy (UPD) occurs when a person receives two copies of a chromosome, or part of a chromosome, from one parent and no copies from the other parent. ...
| Inheritance pattern | Description | Examples | | Autosomal dominant | Only one mutated copy of the gene is needed for a person to be affected by an autosomal dominant disorder. Each affected person usually has one affected parent. There is a 50% chance that a child will inherit the mutated gene. | Huntingtons disease, neurofibromatosis 1 | | Autosomal recessive | Two copies of the gene must be mutated for a person to be affected by an autosomal recessive disorder. An affected person usually has unaffected parents who each carry a single copy of the mutated gene (and are referred to as carriers). Two unaffected people who each carry one copy of the mutated gene have a 25% chance with each pregnancy of having a child affected by the disorder. | cystic fibrosis, sickle cell anemia | | X-linked dominant | X-linked dominant disorders are caused by mutations in genes on the X chromosome. Only a few disorders have this inheritance pattern. Females are more frequently affected than males, and the chance of passing on an X-linked dominant disorder differs between men and women. The sons of a man with an X-linked dominant disorder will not be affected, and his daughters will all inherit the condition. A woman with an X-linked dominant disorder has a 50% chance of having an affected daughter or son with each pregnancy | X-linked hypophosphatemia | | X-linked recessive | X-linked recessive disorders are also caused by mutations in genes on the X chromosome. Males are more frequently affected than females, and the chance of passing on the disorder differs between men and women. The sons of a man with an X-linked recessive disorder will not be affected, and his daughters will carry one copy of the mutated gene. With each pregnancy, a woman who carries an X-linked recessive disorder has a 50% chance of having sons who are affected and a 50% chance of having daughters who carry one copy of the mutated gene. | hemophilia A, Duchenne muscular dystrophy | | Mitochondrial | This type of inheritance, also known as maternal inheritance, applies to genes in mitochondrial DNA. Because only egg cells contribute mitochondria to the developing embryo, only females can pass on mitochondrial conditions to their children. | Leber's hereditary optic neuropathy (LHON) | Sickle-shaped red blood cells Sickle cell anemia (American English), sickle cell anaemia (British English) or sickle cell disease is a genetic disease in which red blood cells may change shape under certain circumstances. ...
The human X chromosome, is is one of the two chromosomes involved in the XY sex-determination system. ...
Hypophosphatemia is an electrolyte disturbance in which there is an abnormally depleted level of phosphate in the blood. ...
Haemophilia A (also spelt Hemophilia A or Hæmophilia A) is a blood clotting disorder caused by a mutation of the Factor VIII gene, leading to a deficiency in Factor VIII. It is the most common hemophilia. ...
Duchenne muscular dystrophy (also known as pseudohypertrophic muscular dystrophy or muscular dystrophy - Duchenne type) is an inherited disorder characterized by rapidly progressive muscle weakness which starts in the legs and pelvis and later affects the whole body. ...
Mitochondrial DNA (mtDNA) is DNA which is not located in the nucleus of the cell but in the mitochondria. ...
Multifactoral and polygenic disorders Genetic disorders may also be complex, multifactorial or polygenic, this means that they are likely associated with the effects of multiple genes in combination with lifestyle and environmental factors. Multifactoral disorders include heart disease and diabetes. Although complex disorders often cluster in families, they do not have a clear-cut pattern of inheritance. This makes it difficult to determine a person’s risk of inheriting or passing on these disorders. Complex disorders are also difficult to study and treat because the specific factors that cause most of these disorders have not yet been identified. Coronary heart disease (CHD), also called coronary artery disease (CAD) and atherosclerotic heart disease, is the end result of the accumulation of atheromatous plaques within the walls of the arteries that supply the myocardium (the muscle of the heart). ...
This article is about the disease that features high blood sugar. ...
Examples of polygenic disorders in humans include:
This article is about the disease that features high blood sugar. ...
In medicine, hypertension refers to the problem of abnormally high blood pressure. ...
Manic depression, with its two principal sub-types, bipolar disorder and major depression, was first clinically described near the end of the 19th century by psychiatrist Emil Kraepelin, who published his account of the disease in his Textbook of Psychiatry. ...
Chromosomal disorders Changes that affect entire chromosomes or segments of chromosomes can cause problems with growth, development, and function of the body's systems. These changes can affect many genes along the chromosome and alter the proteins made by those genes. Conditions caused by a change in the number or structure of chromosomes are known as chromosomal disorders. Figure 1: Chromosome. ...
Some chromosomal conditions are caused by changes in the number of chromosomes, called aneuploidy. These changes are not inherited, but occur as random events during the formation of reproductive cells (eggs and sperm). An error in cell division called nondisjunction results in reproductive cells with an abnormal number of chromosomes. For example, a reproductive cell may accidentally gain or lose one copy of a chromosome. If one of these atypical reproductive cells contributes to the genetic makeup of a child, the child will have an extra (trisomy) or missing chromosome (monosomy) in each of the body’s cells. Aneuploidy is a chromosomal state where abnormal numbers of specific chromosomes or chromosome sets exists within the nucleus. ...
A human ovum An ovum (also oocyte, ovocyte, or loosely, egg or egg cell) is a female sex cell or gamete. ...
Schematic diagram of a sperm cell, showing the (1) acrosome, (2) cell membrane, (3) nucleus, (4) mitochondria, and (5) flagellum (tail) A sperm cell, or spermatozoon ( spermatozoa) (in Greek: sperm = semen and zoon = alive), is the haploid cell that is the male gamete. ...
Cell division is the process of a biological cell (called a mother cell) dividing into two daughter cells. ...
A trisomy means the presence of three (instead of the normal two) chromosomes of a particular numbered type in an organism. ...
Chromosomal disorders can also be caused by changes in chromosome structure. These changes are caused by the breakage and reunion of chromosome segments when an egg or sperm cell is formed or in early fetal development. Pieces of DNA can be rearranged within one chromosome, or transferred between two or more chromosomes. The effects of structural changes depend on their size and location. Many different structural changes are possible; some cause medical problems, while others may have no effect on a person’s health. Fetus at eight weeks A fetus (alternatively foetus or fœtus) is an embryo in later stages of development, from the third month of pregnancy until birth in humans. ...
Although it is possible to inherit some types of chromosomal abnormalities, most chromosomal disorders are not passed from one generation to the next.
See also The following is a list of genetic disorders and their origins. ...
External links - Genetic Disease Information from the Human Genome Project (http://www.ornl.gov/hgmis/medicine/assist.html) This article incorporates public domain text from The U.S. National Library of Medicine (http://ghr.nlm.nih.gov)
- Genes and Disease (http://www.wellcome.ac.uk/en/genome/genesandbody/gb_genesanddisease.html) from the Wellcome Trust
- Polygenic and multifactorial disease (http://www.wellcome.ac.uk/en/genome/genesandbody/hg06b010.html) from the Wellcome Trust
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