Genetic conditions are the result of mutations or changes in a person's DNA. Genetic disorders are illnesses caused by abnormalities in the genes or chromosomes. When a genetic disease is inherited it is due to mutation in the body's germ cells. These are the cells responsible for passing genetic information from the parents to the offspring. Genetic disease can also be caused by changes in the DNA in cells in the body that are not germ cells, or somatic cells.
Genetic diseases caused by mutations occurring in the DNA sequence of a single gene are called Mendelian disorders. Mendelian disorders are usually rare diseases such as Huntington's disease and cystic fibrosis. Other genetic diseases are caused by mutations in several genes compounded by environmental factors such as heart disease and cancer.
Autosomal Dominant Inheritance
When a genetic disorder is diagnosed within a family, the chances of a disorder being passed to the children are increased. Although it is difficult to predict, certain factors will influence the person's chances of developing the disorder.
Autosomal dominant inheritance is one such cause. The majority of genes come in pairs. One of each being inherited by both the mother and the father. Autosomal dominant inheritance is caused by a mutated gene that is located in one of the autosomes. Autosomes are chromosome pairs 1 through 22. This means that the disorder has come from one of your parents. With a mutation in just one of the copies of a gene, an increase of odds for the person to develop a disorder or disease such as developing heart disease is threatened. When one parent is affected by a dominant gene mutation, she carries a 50 percent chance of passing the trait to her children.
Many conditions follow this pattern of inheritance in families. While some of the conditions are obvious at birth, other conditions do not appear until later in life. Neurofibromatosis type 1, Huntington disease, achondroplasia, inherited predisposition to breast, ovarian and bowel cancers and familial hypercholesterolemia all follow autosomal dominant inheritance pattern.
For a small number of conditions, it is possible to test to determine if a person is carrying an autosomal dominant gene mutant gene.
For other conditions, such as breast cancer, determining inherited predisposition, testing for the mutant gene will show an increased risk for the person developing the condition, but will not be a certainty.
Autosomal Recessive Inheritance
Autosomal recessive inheritance is another cause. This too, is when a gene that carries the mutation is in one of the chromosome pairs 1 to 22. Recessive means that the person has received the mutated gene copy from each of his parents and develops the trait. An individual that has inherited one recessive gene mutation is a "carrier," meaning he can pass the trait or disease onto his children, but have no health problems due to carrying the one mutation. Many times the carrier is unaware until she has a child born with the trait or disease. Once a child is born to parents with a recessive disease, there is a 25 percent chance of another child being born with the disease.
Cystic fibrosis, Tay-Sachs disease, thalassaemia, and hereditary haemochromatosis are a few of autosomal recessive inheritance conditions. Men and women are equally affected by this disease.
Testing for automosomal recessive inheritance to see if a person is a carrier can be done. Testing will vary. With some cases, analyzing of the gene product can be in the gene itself to determine if it is mutant. Genetic carrier testing is only considered appropriate when there is an indication that the person may be a carrier of some particular mutant gene.
Examples would be:
1. A family history of the condition.
2. When a condition is more common in people of certain ethic groups or cultural backgrounds.
For couple when both partners are genetic carriers of the autosomal recessive condition, they should speak to their doctor regarding the risks of their children being affected and discuss their reproductive options with a genetic counselor.
X-linked Dominant Inheritance
X-linked dominant inheritance differs in men and women as men have one X chromosome and one Y chromosome and women have two X chromosomes. Men pass their Y chromosome to their daughters and their X chromosome to their sons. For this reason, when a father has an X-linked dominant disorder will not be affected, but his daughters will inherit the condition. The mother passes on one of the other X chromosomes to each child. Thus, a mother with an X-linked dominant disorder has a 50 percent chance of both a son or a daughter affected by the disorder.
There are very few X-linked dominant inheritance conditions that have shown to follow the pattern. However, Rett syndrome is one example. Rett syndrome falls under the classification autism. Among, clinical features head growth rate is accelerated and the person has small feet and small hands. Girls with Rett Syndrome are prone to develop gastrointestinal disorders and records show that up to 80 percent of them have seizures. Typically they do not have verbal skills and in for about 50 percent of females there is no improvement. Scoliosis, constipation and growth failure are all common.
X-Linked Recessive Inheritance
X-linked recessive inheritance differs between males and females. Male children of men will not be affected by an X-linked recessive disorder, however, daughters of the man will carry one copy of the mutated gene. For the female who has an X-linked recessive disorder, there will be a 50 percent chance of her sons being affected and a 50 percent chance that her daughters will be a carrier of one copy of the mutated gene.
Inheritance patterns in families of conditions due to faulty genes
Inheritance pattern of Inheritance patterns in families of conditions due to faulty genes
Heemophilia, Becker and Duchemne types of muscular dystrophy and fragile X syndrome all follow a patter of X linked recessive inheritance.
By following the birth of the first affected boy in a family, carriers of X-linked mutant genes can be detected. Genetic testing can be performed to determine if a woman is a carrier of the X-linked recessive mutant gene or not. This can also provide information for additional family members and in planning their future pregnancies. In some cases, the gene product is analyzed and in some cases the gene itself is, to determine if the mutant gene is present.
Codominant Inheritance
Codominant Inheritance is when each of the parents contributes a different version of a particular gene, and both have an influence on the resulting genetic trait. Whether one is to develop a genetic condition through codominant inheritance and the condition's characteristic features will depend on which versions of the gene are passed to the child via the parents.
Sickle cell anemia is an example of a codominant inheritance condition. Sickle cell anemia is a disease which is due to a blood disorder and is characterized by red blood cells that are abnormal. The disease is life-long. The cells assume an rigid, sickle shape. Sickling is responsible for decreasing the flexibility of the cells' and thus consequently in a risk of various complications. The sickling is due to a mutation in the hemoglobin gene. Life expectancy is shortened and for the male it averages from 42 to 48 years of age and for females, respectively.
Mitochondria
Mitochondria are the energy producing centers within the cells, with each containing a small amount of DNA. Mitochondrial disorders result because of mitochondrial DNA mutations. Both males and females can be affected by mitochondrial disorders, but only the females pass the mutations of the mitochondrial DNA mutations to their children. The female will pass the disorder to all of her sons and daughters, while the children of the man with a mitochondrial disorder will not inherit the mutation.
Mitochondrion are often referred to as "cellular power plants" as they generate the majority of the cell's supply of adenosine triphosphate, used as a source of chemical energy. Mitochondria are involved in processes such as signaling, cell depth, cellular differentiation, as well as the control of the cell cycle and cell growth. Mitochondria have been implicated in several human diseases, including mitochondrial disorders and cardiac dysfunction, and may also play a role in the aging process.
Summary
With each pregnancy the chances of passing a genetic condition to the child are equal. For example, if parents gives birth to a child with an autosomal recessive disorder, the risk of having another child with a autosomal recessive disorder is still 25 percent, just as having a child without the disorder does not decrease the chances of another child being born without the disorder.
Factors that will weigh in inheriting a genetic condition will include the person's family history and results of genetic testing, which can sometimes modify chances of inheritance. In addition, carriers that never develop health problems from the condition or only experience mild symptoms of the disorder. Without a clear cut inheritance pattern of the disease, predicting the odds of a person developing the condition is difficult.
Tags: mutant gene, percent chance, mutated gene, recessive disorder, X-linked recessive
