Abnormalities in genes or chromosomes leads to expression of genetic disorders. These genetic disorders do not necessarily express themselves at birth. There are a few disorders that make an appearance later in life. There are different types of genetic mutations that lead to expression of these genetic conditions. Of these, recessive genetic disorders occur only when both parents carry the mutated gene and pass it on to their child.
What are Autosomal Recessive Genetic Disorders?
Autosomal recessive disorders are those conditions that appear only when the child receives two copies of an autosomal gene. These two defective or abnormal gene copies are from each parent. These genes are present on the autosomal chromosome. The autosomal recessive inheritance includes a 25% chance of the child inheriting the abnormal genes, if both parents are carriers of the gene. There is 505% chance the child will inherit only one abnormal gene and become a carrier and a 25% chance that the child will inherit both a pair of normal genes.
List of Recessive Genetic Disorders
Autosomal recessive disorders occur when there is an abnormality in a gene copy, donated by both parents. Parents who carry the gene, but themselves do not suffer from the condition are called carriers or 'heterozygotes'. When the child that inherits both the abnormal gene copies from parents is called 'homozygote'. Some of the disorders in humans are as follows:
One of the most commonly inherited gene disorders in Caucasians of northern European origins is cystic fibrosis (CF). It is caused by mutation in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. This condition causes the person to secrete abnormal amounts of body fluids like sweat and mucus. The mucus starts affecting the internal organ functioning leading to chronic infections. It also affects the pancreas that leads to decrease in absorption of essential nutrients in the body. The life expectancy of this autosomal recessive disorder has improved considerably since the last few years. This is due to the advancement of medical science related to the management of this condition.
Sickle Cell Anemia
Sickle cell anemia (SC) is a blood disorder where the structure of hemoglobin is abnormal. Hemoglobin is a very important protein that helps in carrying oxygen from the lungs to each and very part of the body. In case of sickle-cell anemia, the shape of the hemoglobin turns to a crescent shape or sickle shape, instead of the normal round shape. This causes the red blood cells to be destroyed sooner than the normal red blood cells. Sickle cells survive for only 15 days, whereas normal RBCs live up to 120 days. Thus, the affected person regularly becomes anemic due to lack of red blood cells. It causes the affected person to suffer from frequent infections, severe pain in the arms, legs, back and stomach. It also makes them vulnerable to mild jaundice and development of gallstones, stroke and eye problems.
Tay-Sachs disease is a fatal disorder that causes death of the affected child by the age of 5 years. This condition leads to progressive degeneration of the central nervous system. The degeneration occurs due to absence of an enzyme called hexosaminidase A (hex A). If Hex A is not present in the body, it causes fatty substances to start building up on the nerve cells, especially in the brain. This condition starts occurring when the baby is still in the womb. However, the condition becomes apparent only after several months of birth. Till date, there is no cure found for treatment of Tay Sachs disease.
Gaucher's disease is a genetic disease that causes accumulation of fatty substances in the cells and organs. This condition occurs due to deficiency of an enzyme called glucocerebrosidase. In absence of the enzyme, the fatty substances accumulate in the white blood cells, spleen, liver, kidneys, brain, lungs and bone marrow. Thus, it leads to skeletal disorders, enlarged spleen, neurological complications, anemia, low platelet count, etc. It affects about 1 in 100 people born in United States.
Phenylketonuria (PKU) is an autosomal recessive metabolic disorder. It occurs due to the abnormal coding of enzyme phenylalanine hydroxylase (PAH). This causes the enzyme to become nonfunctional and leads to accumulation of the amino acid phenylalanine.
These are some of the recessive genetic disorders that affect many children and adults around the world. Some other conditions include Mucopolysaccharidosis (MPS), Osteogenesis imperfecta, Fanconi anemia, Ehlers-Danlos syndrome. One should undergo genetic counseling, especially when either of the partner has a family history of genetic disease. This will help reduce the chances of the child developing the disease or becoming a carrier of the genetic disorder.