Autosomal Recessive Disorders: Types, Symptoms, Diagnosis
Think of autosomal recessive disorders as sneaky and secretive for now. However, in order to fully appreciate autosomal recessive disorders, the types, symptoms and diagnoses, let us first break down ‘autosomal recessive’ and go from there.
Every one of us has a set of 23 chromosome pairs. Chromosomes 1-22 are called autosomes, while chromosome 23 is a sex chromosome. In females, the sex chromosome is the X chromosome, whereby females carry two copies (XX), while in males the 23rd chromosome is a Y chromosome, and males carry one of each (XY). Autosomes do not have an effect on the gender of the children, while sex chromosomes do. It is said that we have chromosome pairs because we inherit half of our genetic material from the mother and the other half from the father. This also means that we have two copies of every single gene on each of the chromosomes. Every gene codes for specific characteristics, and depending on the type, we either need two copies of the gene that codes for a trait or one copy that is enough for the trait to be expressed.
In the case of the former, if two copies of the gene are needed for a trait to be outwardly expressed or visible, the gene is said to be recessive. In the case of latter, or if just one copy of the gene is enough to be expressed, that gene is said to be dominant. Furthermore, this means that a person who has two genes, one dominant and one recessive, will only have a characteristic of the dominant gene. This also means that people can be ‘carriers’ of a gene and pass it on to their children without it showing among their outward characteristics. In fact, most individuals are not even aware of the fact that they are carriers of a recessive mutation until they either have children or other family members of that mutation. So, in yet other words, autosomal recessive inheritance is inheriting a recessive genetic mutation on one of the 22 autosome pairs. Approximately five or more recessive genes that cause genetic diseases or conditions are carried by all of us. Furthermore, parents who are carriers of the autosomal recessive mutation have a 25% chance that they will have an affected child. On the other hand, this also means that there is a 75% chance that the children of each successive pregnancy will not have the disease.
So what are autosomal recessive disorders? Genetic mutations have happened over the course off time all over the world, and anyone can be a carrier of any type of recessive gene. However, depending on the origin of the mutation, certain cultures are much more likely to be carriers. For example, the mutation for Tay-Sachs disease is estimated to have originated in Eastern Europe, which is why the disease is much more prevalent among Ashkenazi Jews as well as others who live in that region of the world.
There are several different types of autosomal disorders, and we will get into a few of them here. Those include Tay-Sachs disease, cystic fibrosis, and sickle cell anemia.
Tay-Sachs disease is a deadly condition affecting children by the age of five, and it is a process that starts very early during the pregnancy during a baby’s development and is only apparent after several months following birth. It is marked by a degenerating nervous system that results from a missing enzyme, namely hexosaminidase A (or hex A). Without this enzyme, the nerve cells in the body (and particularly in the brain) accumulate a fatty substance. Currently, Tay-Sachs disease cannot be cured, and about 1 in 27 of those with European Ashkenazi Jewish ancestry are carriers the Tay-Sachs genetic mutation.
This is a common disorder among Caucasians. It is inherited, and it is one of the single-gene disorders we have mentioned earlier in the post. Symptoms of cystic fibrosis include production of an abnormally viscous and sticky mucus that is detrimental to body organs. Affected organs include the lungs, in particular, whereby the mucus results in chronic and repeated infections. Cystic fibrosis also affects the pancreas, leading to a lower absorption of nutrients that are needed for survival. This can also lead to problems in the reproductive system. While cystic fibrosis is not exactly treatable, it can be managed and those who are affected can survive to adulthood. Respiratory failure is the most frequent cause of death among those who have the disease.
Sickle cell anemia
This disorder is a very common and inherited disorder that mostly affects individuals of African American origin. It is another example of a single-gene disorder that affects approximately 1 in 500 African American babies with nearly 1 in 12 African Americans being carriers of the mutation. The condition is marked by the inability of red blood cells to carry oxygen to organs within the body. While the appearance of normal red blood cells is smooth, round, and flexible, sickle cells are stiff and also sticky and cannot move through the body as easily as normal red blood cells. This means that they eventually accumulate in blood vessels, causing blockages and thereby stopping the movement of healthy and normal blood that carries oxygen. This has detrimental side effects as each organ of the body depends on oxygen for proper functioning. Individuals with sickle cell disease are typically anemic. These abnormal cells eventually wreak havoc on the spleen and eventually cause it to stop functioning. This, in turn, renders affected individuals much more likely to suffer from infections. Infants and younger children are particularly vulnerable as those affections can be deadly. Treatment for sickle cell disease typically starts out with emergency care for fevers and infections. It also involves specific vaccinations, penicillin as well as keeping anemia under control.