'Autosomal' refers to the genetic defect that occurs among any of the first 22 chromosomes, excluding the 23rd sex-linked chromosome. The term 'recessive' means that the affected person should have two copies of the affected gene―one from each parent―in order to inherit the genetic disease.
So, autosomal recessive inheritance means inheritance of two copies of an abnormal gene, which leads to development of a genetic trait or disease.
It is necessary for the person to inherit both the affected genes, each from the father, and the mother. In spite of having an mutated gene, the parent may not have the traits or diseases, because the healthy gene can balance the health of the person. Mentioned next is the pattern of inheriting autosomal recessive genetic diseases, and how it usually works.
❖ If both the parents are carriers, meaning, they have 1 abnormal gene each, then there are 25% chances that the child will have the disease (have two abnormal gene, one from each parent).
On the other hand, there are 50% chances that the child will be a carrier (have one affected gene and one healthy gene, but have no disease), and again, there are 25% percent chances that the child will neither be the carrier, nor have the disease (have both healthy genes).
❖ If only one parent is the carrier, and the other parent is unaffected, then there are 50% chances for the child to be the carrier, however, in no way can he be affected by the resultant traits or diseases.
❖ If one of the parent is a carrier, and the other parent has the disease, then there are 50-50 chances for the child to either have the disease, or be the carrier. In any case, he will be affected.
To explain it in a better way, let us take an example: There is a couple that carries the abnormal gene, but none of them is affected by the disease. What can be the chances of their children having autosomal recessive diseases? Let us say that they have 4 children, the pattern of autosomal recessive inheritance would be -
- 1 out of the 4 children will have both normal genes, meaning he will be unaffected.
- 2 out of the 4 children will contain one normal and one abnormal gene. Which means that they will be carriers but will not have the disease.
- Lastly, 1 out of the 4 children will have both abnormal genes, that means he might inherit the disease.
Some examples of such diseases include: Sickle Cell Anemia, Osteogenesis Imperfecta (brittle bone disease), Cystic Fibrosis (affects secretory glands), Congenital Neutropenia (blood disorder), and Alport Syndrome (kidney disease).
A point to be noted is that not all genetic diseases and disorders are related to autosomal recessive inheritance. An example for the same would be the 'Sporadic Genetic Disease', which can occur in children, in spite of no genetic abnormalities in the parents. In order to call a disease autosomal recessive, the genes of both the parents should be affected.
Another important point here, is that this condition is not gender biased, meaning, it can be found in both males and females because the abnormality does not occur in the 23rd sex chromosome. Researchers are still trying to explore the many facets of human genetics, many facts that are unexplored will soon come into light as technology advances.
Disclaimer: This post is meant for informational purposes only and should not be considered as a replacement for expert medical advice.