Genetic disorders are caused by changes in the DNA sequence, partial or whole, resulting in abnormal DNA sequences. They may be caused by a variation in a single gene (monogenic disorder), by mutations in multiple genes (multifactorial inheritance disorder), by a combination of gene mutations and environmental factors, or by damage to chromosomes.
With the rapidly progressing field of genetics and genomics, we now know that genetics is a major factor affecting health. Some diseases may be caused by genetic mutations or germline mutations, passed on to offspring, such as cystic fibrosis and certain cancers. On the other hand, several cancers result from somatic mutations, of which causes include exposure to toxic environments, certain viral infections and aging.
Common genetic disorders
There are several types of genetic disorders depending on the genetic material abnormality. But common ones are the following:
- Polycystic kidney disease is caused by the defect in the PKD1 gene, causing the patient to have a large number of cysts in the kidneys, which increases over time. The cysts of different sizes may spread all over the kidneys, reducing renal function, developing into chronic kidney disease in the late stages, then kidney failure and death. It also causes complications such as high blood pressure, gallstones, and infections. Those with hereditary PKD may show no symptoms for decades and then begin to develop symptoms in their 30-40s.
- Sickle cell disease is caused by mutation in genes, causing a red blood cell disorder, making the cells of sickle shape, unhealthy, short-lived and break apart easily. This leads to anemia and also causes arm pain, swollen feet, and life-threatening complications such as liver failure, pulmonary hypertension, and cerebrovascular disease.
- Cystic fibrosis is a genetic condition caused by a mutation in CFTR gene The body thus produces thick and sticky mucus, clogging the lungs, which can lead to difficulty breathing and severe lung infections. The sticky mucus also blocks the secretion of enzymes used to digest food in the pancreas, causing problems with the digestive system and then a lack of key nutrients. The mucus also clogs the ducts connecting the testicles to the prostate resulting in male infertility. Women with cystic fibrosis will find it difficult to get pregnant.
- Huntington's disease is caused by a mutation in the Huntington gene and its production of abnormal proteins, resulting in the degeneration of nerve cells in the brain, and in turn, movement, cognitive, and psychiatric disorders. Functional abilities keep worsening until the person finds it hard to move or self-care and suffers from dementia. Risks of complications include heart disease, pneumonia and falls. Patients usually die within 20 years of the onset of symptoms.
- Thalassemia is a type of anemia caused when the body makes an abnormal form or inadequate amount of hemoglobin in red blood cells. A person with Thalassemia usually has pale or yellowish skin and in mild cases, can lead a normal life. But in severe cases, the person may suffer from facial bone deformities, slow growth, enlarged liver and spleen, vulnerability to infection, and brittle bones.
- Hemophilia is a malfunction of the genes affecting the coagulation factors, causing easy bleeding, which is then hard to stop. It is a disorder found only in men as women who is a carrier of the hemophilia gene are asymptomatic. Symptoms vary depending on the severity of the disease. In mild cases, heavy bleeding may occur only after an accident, a surgery or a tooth extraction, when the bleeding is found hard to stop. In severe cases, the patient has bruises all over the body, bleeding in the muscles and joints, and possibly bleeding in other organs such as the gastrointestinal tract and the brain.
- Down syndrome is condition in which a child is born with an extra full or partial copy of their 21st chromosome, causing physical and mental developmental delays. Common physical characteristics include a flat facial feature, bulging tongue, small head and ears, upward slanting eyes, short neck, round face, plus short and wide hands. Children with Down syndrome are short and tend to be overweighed growing up. Complications include congenital heart disease, thyroid disease, hearing loss, cataract and dementia as well as vulnerability to infections. Risks of giving birth to a child with Down syndrome include the expecting mother being over 35, the mother previously having a child with Down syndrome, or with a family history of Down syndrome.
- Color blindness (Color vision deficiency) is the decreased ability to see color or differences in color. The most common cause of color blindness is a genetic disorder in the development of one or more of the three sets of the eyes' cone cells, which sense color. These cone cells sense wavelengths of light and enable the retina to distinguish between colors. Abnormal photoreceptor cells thus cause impaired color vision. Most patients cannot distinguish between red and green. In severe cases, the patients may see things only as black and white or in shades of gray.
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Cancer is caused by mutations in genes, accelerating cell division rates or inhibiting normal controls on the cell cycle. Gene mutations can be spontaneous or triggered by environmental pollution or exposure to carcinogens. Gene mutations can also be inherited from parents to offspring. When transmitted to a child, a germline mutation is incorporated in every cell of the body. Common genetically inherited cancers include breast cancer, uterine cancer, retinoblastoma, pancreatic cancer, ovarian cancer, colorectal cancer, prostate cancer and thyroid cancer.
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Genes regulate many aspects of the cardiovascular functions. Cardiovascular diseases can ensue from a gene mutation. Several of such diseases can be inherited, including arrhythmias, congenital heart disease, hypertrophic cardiomyopathy (HCM), idiopathic dilated cardiomyopathy (DCM), hyperlipidemia, coronary artery disease, and heart failure. Thus, in a family where a member has a heart disease especially at a young age or sudden death, other family members are recommended to be tested for the risk of developing a heart disease even without any symptoms.
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Drug allergy risk
Different people respond differently to a drug. Some drugs may be more effective in one person than in another. Also, some people may have an overreaction to the drug, known as a drug allergy. Symptoms range from mild to moderate including rash, swelling, fever, to severe allergic reactions which could result in abnormal and life-threatening conditions such as bronchospasm, causing difficulty breathing, swollen tongue blocking airway, diarrhea, low blood pressure, seizures and loss of awareness, etc. Genetic testing allows doctors to choose the most appropriate drugs for the patient so as to avoid drug allergy. This further helps save treatment time and cost as appropriate drugs can be prescribed right from the start without trial and error.
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