Genetic testing is a method of genetic diagnosis to check for the susceptibility to hereditary diseases and can also be used to establish the ancestry of any person. Genetic testing studies the chromosome, breaking it to individual genes. In a broader sense, it can be used as a biochemical test for scrutinizing the existence and nonexistence of main proteins that hint abnormalities of certain genes. Genetic testing studies the abnormality in the chromosomes, genes or proteins. It can be used to find out whether a particular genetic condition is developing and it's chances of being passed over to the future generations.
The most widely used type of genetic testing is newborn screening. Genetic testing during pregnancies is called as prenatal genetic testing and is performed during pregnancy to screen or identify birth defects. This provides ample information on the developing fetus both for the parents and the physician. Amniocentesis and chorionic villus sampling is the common diagnostic test performed to diagnose any defect in the fetus. These diagnostic tests are ordered for if the triple test (AFP test, hCG blood test, and UE3) returns abnormal results.
Charcot MarieTooth Disease
Charcot MarieTooth disease or CMT, also called as hereditary motor and sensory neuropathy, is a group of inherited disorders that cause damage to peripheral nerves. The disease is named after three physicians Jean Charcot, Pierre Marie, and Howard Henry Tooth, who researched about the condition. The condition is progressive, meaning, the muscles of the arms and legs of CMT patients become weak over a period of time. CMT is a genetic disorder and is caused by many different gene mutations. Since 1991, 90 different genes causing CMT have been identified and the list continues to grow.
Signs and symptoms
CMT patients usually begin to notice symptoms in adolescence or early adulthood. Charcot MarieTooth disease affects both motor and sensory nerves and hence results into both motor symptoms (weakness and muscle wasting) and sensory symptoms such as numbness and tingling in extremities. Very rare symptoms of CMT include breathing problems, hearing loss, speech and swallowing problems.
Diagnosis and treatment
Examining patient's medical history and family history forms the basis for diagnosing Charcot MarieTooth disease. After noting down the symptoms, doctor may further order nerve conduction studies, electromyography (EMG), nerve biopsy, genetic testing and bone X-rays. Nerve biopsy might be done to check for appearance of CMT. Genetic testing is used to check for mutations that cause CMT.
CMT is not a fatal disease and people with most forms of CMT have normal life expectancy. However there is no cure for Charcot MarieTooth disease. It only needs to be managed depending upon the symptoms of the patient. Physiotherapy plays a major role in improving the condition of CMT patients. Physical therapy involving stretches and light exercises helps in building muscle strength and preventing atrophy. Depending on the symptoms, orthopaedic devices such as splints and braces may be used to maintain the mobility of the limbs. If the patients have severe foot deformity, it can be rectified through surgery to help them walk with ease. It can be supported with use of orthotics - specialized shoes.
Haemochromatosis is characterized by excess iron in the body. Just like lack of iron can cause anemia, excessive levels of iron in the blood are toxic. The effects are damaging since the iron mineral starts building up in the tissue. In many cases, Hemochromatosis is caused due to an inherited abnormality that causes the body to increase absorption of iron from the intestine. This condition is called primary Hemochromatosis. Secondary Hemochromatosis occurs when abnormal red blood cells in the body are destroyed and iron is released.
Causes : Hereditary Hemochromatosis is an autosomal recessive condition. This Hemochromatosis which is known as iron overload, bronze diabetes, hereditary Hemochromatosis and familial Hemochromatosis. Hemochromatosis afflicts nearly 1.5 million people in the United States and it is one of the most common genetic disorders in the US. Approximately one in 9 persons have one abnormal Hemochromatosis gene which works out to 11% of the US population. Since all of us have 2 copies of each gene, these individuals have an abnormal HFE gene and a normal gene. Thus they are called as carriers. Between 1/200 and 1/400 individuals have two abnormal genes for Hemochromatosis and no normal gene. The culprit gene is on chromosome 6, known as HFE.
As it is an autosomal recessive condition, siblings of the Hemochromatosis patients are at 25% risk to be affected as well. But the chances of the person to develop symptoms depends on which gene mutation s/he has in addition to environmental factors. The 2 most common changes in the HFE gene are C282Y and H63D. To complicate things further, the age at which symptoms show up vary widely even within the same family.
Idiopathic Pulmonary Hemosiderosis (IPH), a disorder affecting largely children and young adults, is a similar disorder owing to abnormal accumulation of hemosiderin. Hemosiderin is a protein found in most tissues, but primarily in the liver. It is produced by digestion of hematin, an iron related substance.
Although it affects both sexes in equal proportion, women suffer later in their lives because of the blood loss in menstruation and child birth in their younger ages. This iron dose overload usually affects people in the age group of 30 - 60 years. It is essential to treat this condition lest it lead to heart failure or cirrhosis of the liver. 5% of cirrhosis cases are caused by hereditary Hemochromatosis.
In Hemochromatosis, as the excess iron is deposited in the liver, pancreas, heart, endocrine glands, skin, joints and intestinal lining, it may result in toxicity of the affected organs. Persons suffering from Hemochromatosis tend to feel fatigue and lethargy. There might be joint pain or arthritis. Men might notice impotence and reduced sex drive. Other symptoms of Hemochromatosis are loss of body hair and darkening of skin. Cirrhosis of the liver might occur due to scarring of liver. This is accompanied by abdominal pain, jaundice and enlargement of the liver and spleen. Haemochromatosis can lead to heart failure or abnormal heart rhythms. The patient may show symptoms similar to heart failure, diabetes or cirrhosis of the liver. Changes in the pigment of the skin may occur, like grayness or a tanned/yellow appearance. Idiopathic pulmonary hemosiderosis appears as paleness of the skin. At times, the patient may start spitting of blood from the lungs or bronchial tubes.
Diagnosis: Hemochromatosis is diagnosed through blood tests and liver biopsy. The usual diagnostic methods are genetic blood studies, blood studies of iron, Magnetic Resonance Imaging (MRI), and liver biopsy. Blood studies of transferrin iron saturation and ferritin (a protein that transports iron and liver enzymes) concentration are used to screen for iron overload. Genetic testing is a reliable technique of diagnosis of Hemochromatosis as this method became widely available. Diagnosis of idiopathic pulmonary hemosiderosis begins with blood tests and X-ray studies of the chest area.
Hemochromatosis Treatment: The first option of treatment is therapeutic venesection or phlebotomy ( a process of regular bloodletting, similar to blood donation). Patients may need to undergo these procedures one or two times a week for a year. The frequency of phlebotomy may be reduced subsequently based on the condition of iron build up. For cases of patients who cannot tolerate phlebotomy owing to other medical conditions can be treated with Desferal (Desferrioxamine). Patients suffering from Haemochromatosis must limit the consumption of iron. Some times chelating agents may be prescribed to control the absorption of iron. Excess alcohol consumption must be avoided. Avoid iron supplements and Vitamin C, which aids absorption of iron. Reduction in the intake of supplements containing iron and foods such as uncooked sea food may help manage this condition.
Prevention: Genetic testing might be the most helpful as variable severity has been noted in patients who have 2 C282Y genes compared to patients with 2 H63D genes or one of each. The best screening method may be iron and ferritin studies which are cost effective for the susceptible group of people. At the end of the day, Hemochromatisis is a common, easily and effectively treated condition. The complications arise in diagnosis as the symptoms mimic other medical conditions.
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Bibliography / Reference
Collection of Pages - Last revised Date: August 8, 2020