Autosomal dominant genetic disorder is a genetic condition where just a single copy of mutant allele is required to express the defect in the progeny. The following article will explain more about the inheritance this genetic disease.
Genes contain the instructions that help in formation of an organism. Each and every cell in the body contains a complete set of genes. There are thousands of genes in our bodies that contain information related the phenotypic as well as genetic make up of an individual. These genes are passed on from both parents, that is father and mother. Thus, an individual carries phenotypic as well as genetic information containing genes that are actually combination genes from both parents. However, any changes or mutation in the coding of the genes can lead to alteration in reading the information. If this alteration occurs, it causes the gene to function abnormally or stop functioning completely. This leads to expression of a genetic disorder in the baby born. There are different types of inheritance patterns that lead to expression of normal and abnormal characteristic in individuals.
It is not always necessary the genes inherited will lead to a genetic defect. Genes are present on chromosomes that make up our DNA. Thus, they are responsible for each and every characteristic of the body. This includes the color of the eyes, hair, skin color, height, weight, personality, behavior and many more. When the gametes, or sex cells from parents, that is sperms and eggs fuse together they lead to fertilization and formation of an embryo. The sperm contains half the number of chromosomes, that is, 23 chromosome (halpid ‘n’). The other half comes from the mother’s egg. Thus, after fusion the embryo formed contains the complete set of chromosome, that is 46 chromosome in each cell. Of these 23 chromosomes from each parent, 22 chromosomes are called autosomes and the remaining one pair is called sex chromosome. The autosomes are responsible for the expression of phenotypic characters of an individual and sex chromosome decides the gender of the baby. Any mutation or changes in the baby leads to autosomal genetic diseases.
What is Autosomal Dominant Inheritance
When only one gene in a pair of genes undergoes a mutation, and the other remains normal, it tends to compensate for the abnormality. However, this is not true for all cases. Sometimes, a single copy of a mutated gene is enough to lead to a disorder, disease or defect. Such an inheritance pattern where the mutant autosomal gene is expresses itself instead of the normal gene is called an autosomal genetic disorder. It is known as dominant, as the mutated gene dominates over the normal gene.
These genes are passed on to children of parents suffering from a particular condition. These parents may pass on the normal gene to the child. It may even happen that the defect gene is the one passed on to the child from the parent. As this is a random process, there are 50% chances of the child receiving a mutated copy of gene or normal copy of the autosomal gene. In order to understand this pattern of inheritance, you can have a look at the following diagram:
As you can see, there are 50% chances the child may inherit abnormal gene. If this happens, he may express the defect and even pass on the same gene to his children. If the child receives a normal gene, he will be free from any type of disease and will not pass on the trait to his children in future.
In many cases, a child born is the first person in the family to have a dominant genetic disorder. The parents do not carry the mutated gene. But the mutation occurs only in the egg or sperm of the parent. Thus, the chances of another child to the same parents developing these disorders is very low. But, the child who has inherited the gene, will pass on the trait to his next generation. In some cases, the autosomal condition has variable effects. Thus, some children are severely affected, some show mild effects and a few live an asymptomatic life.
Examples of the Genetic Disorder
Some of the disorders include the following conditions:
- Huntington’s disease
- Hereditary nonpolyposis colorectal cancer
- Hereditary multiple exostoses
- Marfan syndrome
Prenatal diagnosis is important to find out if the child has an inherited genetic disease from the parents. Thus, people with genetic conditions should always seek genetic counseling before planning for a baby.