Genetic abnormalities are defined as the presence of one or more abnormal genes. Certain genetic disorders are inherited from parent to child through the genetic makeup of the parents. In addition, there may be sporadic mutations that cause a child to develop a disorder without any family history.
How does a genetic abnormality occur?
There are 46 chromosomes in the human body, and the presence of an abnormal chromosome can cause health problems. An abnormal chromosome is most commonly caused by an error in cell division but can also be caused by one or more other factors, including:
• Errors that occur during the division of sex cells (meiosis)
• Errors that occur during the division of other cells (mitosis)
• Exposure to substances that are known to cause birth defects, such as alcohol, drugs, certain chemicals, etc.
Types of common genetic disorders
Genes are known as the building blocks of heredity. They contain DNA—the instructions for making proteins. In some cases, mutations of a gene or genes occur. A mutation alters the gene’s instructions for producing a protein, causing the protein to malfunction or to be missing altogether. This can lead to a condition known as a genetic disorder. The following are five of the most common genetic disorders:
Down Syndrome: Normally, there are 23 pairs of chromosomes in the nucleus of a single cell. The presence of an extra copy of chromosome 21 in all or certain cells causes Down syndrome. Infants with Down syndrome are likely to have mild to severe cognitive impairments. Other Down syndrome characteristics include a predisposition to heart defects, poor muscle tone, a smaller body size, and an upward tilt of the eyes.
Thalassemia: Thalassaemia is a group of inherited blood disorders that limit the amount of haemoglobin a person can make in their body. There's a 25% chance that a child will have thalassaemia if they inherit the thalassaemia gene from both their parents. Severe anemia is a common occurrence with any type of thalassaemia and may require specialized treatments such as frequent blood transfusions or chelation therapy.
Cystic Fibrosis (CF): Cystic Fibrosis is a long-term, inherited disease characterized by the production of thick, sticky mucus that obstructs the respiratory, gastrointestinal, and reproductive systems of patients. There's a 25% chance that a child will have cystic fibrosis if they inherit the cystic fibrosis gene from both their parents. A stuffy nose, persistent cough (with sputum), wheezing, recurrent lung infections, diarrhea or fatty stools, and weight loss are just a few of the common symptoms of CF.
Tay-Sachs disease: Tay-Sachs disease is a rare genetic disorder passed from parents to children. A defect in chromosome 15 results in this disease, which is known to be fatal when it is present in children. The disease gradually damages the nervous system and usually results in death by the age of five. Late-onset Tay-Sachs disease can be diagnosed in adults and may result in a mild level of cognitive impairment.
Sickle Cell anemia: Sickle Cell disease is a long-term genetic disorder that can be inherited when both parents pass on the sickle cell trait to their offspring. In this condition, red blood cells form a sickle shape. These red blood cells clump together and become trapped in the blood vessels, resulting in a blockage of blood flow. This can deprive the organs of oxygen-rich blood flow, causing organ damage or failure. This condition also causes severe pain and complications like infections and acute respiratory syndrome.
How to prevent chromosomal abnormalities in pregnancy?
Prior to conception, it is recommended to consult with a medical professional to determine the best course of action to ensure the health of the unborn child. Both men and women should abstain from exposure to hazardous substances, including ionizing radiation (IR), alcohol, drugs, etc. Pre-pregnancy genetic testing can be used to determine if an individual is at an increased risk of conceiving a child with a hereditary genetic disorder such as Cystic Fibrosis. If the results of the test indicate an increased risk, the individual may opt for assisted reproductive technologies, such as egg or sperm donation, or choose to undergo in vitro fertilization (IVF) and screen the embryos for genetic disorders prior to implantation.
What is karyotyping and how does it work?
Karyotyping is the process of determining the chromosome size, number, and shape of an individual. This process provides a comprehensive overview of an individual's chromosome, including any abnormalities such as duplication, deletion, translocation, or inversion. Additionally, it can be used to diagnose hereditary diseases, birth defects, immune system disorders, and the cause of male or female infertility.
Karyotype testing can be carried out in a variety of ways, including:
Blood testing: This is the most commonly used method of karyotype testing for adults, children, and infants and involves the collection and testing of a few milliliters (ml) of blood.
Bone aspiration and bone marrow biopsy: It involves the collection of bone marrow samples from individuals to examine whether their sample contains certain forms of cancer and blood disorders, such as leukemia.
Amniocentesis: This is used to test the protective fluid surrounding a developing fetus.
Chorionic Villus Sampling (CVS): This includes testing of cells taken from the placental cord, an organ that connects the baby to the uterus.
Karyotyping test results
It typically takes approximately one to two weeks to receive the results of karyotyping tests. While some chromosomal abnormalities will present with common symptoms, the effects and severity of the condition may vary between individuals and are often unpredictable.
Abnormal test result: An abnormal test result indicates the presence of an abnormal chromosome structure or number (that is, more or less than the normal 46 chromosomes). An abnormal test result on the prenatal screening test may indicate that the fetus has chromosomal abnormalities such as Down Syndrome, which may result in poor pregnancy outcomes.
Normal test result: A normal test result indicates that the individual has a normal number of chromosomes (46 chromosomes) without any structural abnormalities.
Each chromosome is made up of thousands of genes located in specific regions of the chromosome. These genes play a major role in an individual's genetic makeup and play a significant role in their growth, development and function.
Prenatal screening tests performed during pregnancy, such as karyotyping, are used to provide information regarding the presence of any chromosomal abnormality in the fetus and may help to improve prenatal care for the unborn baby.