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Genetic testing

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.

  • Muscle weakness leading to Foot Drop

  • High-stepped gait

  • Frequent tripping and falling

  • Stork-like legs due to muscle atrophy

  • Dropping things

  • Clumsiness

  • Bone deformities

  • Hammertoes and High arches

  • Decreased deep tendon reflexes

  • Sensory loss

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.

Leber Congenital Amaurosis

Leber Congenital Amaurosis or LCA is an inherited retinal degenerative disease that causes severe loss of vision in infants. Retina is located at the back of the eye. It contains photoreceptors called rods and cones, through which retina captures light. It converts the light into chemical signals that go to the brain via the optic nerve to interpret it as an image. In case of Leber Congenital Amaurosis, rods and cones do not develop properly and thereby retina ceases to function effectively causing visual impairment. Though LCA can cause complete blindness, most often, infants are born with residual vision.

LCA is a genetic condition that is transmitted by autosomal recessive pattern in which both the parents carry a defective gene to result in LCA. Infants with LCA usually develop other eye related problems such as roving eye movements known as nystagmus, extreme farsightedness hyperopia, deep-set eyes, and sensitivity to bright light. Leber Congenital Amaurosis is a rare disease and only 3 in every 1,00,000 newborns are said to be affected by this condition.

There are 14 types of genes that are associated with Leber Congenital Amaurosis and mutations in any of these genes hinder the development and effective function of the retina. However mutations in the genes naming CEP290, CRB1, GUCY2D, and RPE65 are the most common causes of the LCA.

Symptoms and diagnosis

Infants with LCA may have roving and sunken eyes, cone-shaped corneas termed as Keratoconus and also exhibit oculo-digital reflex in which they press or poke their eyes regularly. Most infants also have sluggish pupils and hyperopia. Rarely, infants with LCA may also have problems with central nervous system and hearing impairment. They may experience seizure disorders, motor impairments and developmental delays.

With LCA, initially, the eyes of the infant may look normal. The diagnosis process is generally initiated after few weeks of the birth, when the infant fails to respond to the visual stimuli. The LCA cannot be easily diagnosed based on the symptoms alone as many other eye diseases also present with similar warning signs. Electroretinography (ERG) test is usually advised to evaluate the retinal function and diagnose LCA. If ERG results confirm poor retinal function, genetic testing will be performed to confirm Leber Congenital Amaurosis.

Treatment of Leber Congenital Amaurosis

No effective treatment is currently available for Leber Congenital Amaurosis. Palliative and supportive care is normally provided to the patients based on symptoms. Those with slight remaining vision are given low-vision aids, including electronic, computer-based and optical aids.

Tags: #Genetic testing #Charcot MarieTooth Disease #Leber Congenital Amaurosis
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Collection of Pages - Last revised Date: February 25, 2020