Unit 5: Mental Retardation with Associated Conditions
5.1 Fragile X Syndrome
5.2 Downs Syndrome
5.3 Hydro cephaly
5.4 Cretinism
5.5 Progressive Metabolic Disorders
5.1 Fragile X Syndrome
Fragile X syndrome (FXS) is a genetic disorder. A genetic disorder means that there are changes to the person’s genes. FXS is caused by changes in the fragile X mental retardation 1 (FMR1) gene. The FMR1 gene usually makes a protein called fragile X mental retardation protein (FMRP). FMRP is needed for normal brain development. People who have FXS do not make this protein. People who have other fragile X-associated disorders have changes in their FMR1 gene but usually make some of the protein.
Symptoms of Fragile X Syndrome
There are several, including:
Some children with fragile X also have changes to their face and body that can include:
Symptoms are usually milder in girls. While most boys with fragile X have trouble with learning and development, girls usually don't have these issues.
Girls with fragile X sometimes have trouble getting pregnant when they grow up. They might also go into menopause earlier than usual.
The FMR1 gene, which is on the X chromosome, makes a protein called FMR that helps nerve cells talk to one another. A child needs this protein for his brain to develop normally. Children with fragile X make too little or none of it.
People with this condition also have more copies than usual of a DNA segment known as CGG. In most people, this segment repeats five to 40 times. In people with fragile X, it repeats more than 200 times. The more times this DNA segment repeats, the more serious the symptoms are.
A mother with the FMR1 gene change has a 50% chance of passing it to any of her children. A father can only pass it to his daughters.
Boys are more likely to have fragile X than girls, and they have more severe symptoms. This is because girls have two copies of the X chromosome. Even if one X chromosome has the gene change, the other copy can be fine. Boys have one X and one Y chromosome. If the X chromosome has the gene change, they will have symptoms of fragile X syndrome.
Some people inherit the fragile X gene without having symptoms. They are called carriers. Carriers can pass the gene change to their children.
FXS can be diagnosed by testing a person’s DNA from a blood test. A doctor or genetic counselor can order the test. Testing also can be done to find changes in the FMR1 gene that can lead to fragile X-associated disorders.
A diagnosis of FXS can be helpful to the family because it can provide a reason for a child’s intellectual disabilities and behavior problems. This allows the family and other caregivers to learn more about the disorder and manage care so that the child can reach his or her full potential. However, the results of DNA tests can affect other family members and raise many issues. So, anyone who is thinking about FXS testing should consider having genetic counseling prior to getting tested.
5.2 Downs Syndrome
Down syndrome is a genetic disorder caused when abnormal cell division results in an extra full or partial copy of chromosome 21. This extra genetic material causes the developmental changes and physical features of Down syndrome.
Down syndrome varies in severity among individuals, causing lifelong intellectual disability and developmental delays. It's the most common genetic chromosomal disorder and cause of learning disabilities in children. It also commonly causes other medical abnormalities, including heart and gastrointestinal disorders.
Better understanding of Down syndrome and early interventions can greatly increase the quality of life for children and adults with this disorder and help them live fulfilling lives.
Each person with Down syndrome is an individual — intellectual and developmental problems may be mild, moderate or severe. Some people are healthy while others have significant health problems such as serious heart defects.
Children and adults with Down syndrome have distinct facial features. Though not all people with Down syndrome have the same features, some of the more common features include:
· Flattened face
· Small head
· Short neck
· Protruding tongue
· Upward slanting eye lids (palpebral fissures)
· Unusually shaped or small ears
· Poor muscle tone
· Broad, short hands with a single crease in the palm
· Relatively short fingers and small hands and feet
· Excessive flexibility
· Tiny white spots on the colored part (iris) of the eye called Brushfield's spots
· Short height
Infants with Down syndrome may be average size, but typically they grow slowly and remain shorter than other children the same age.
Most children with Down syndrome have mild to moderate cognitive impairment. Language is delayed, and both short and long-term memory is affected.
Causes
Human cells normally contain 23 pairs of chromosomes. One chromosome in each pair comes from your father, the other from your mother.
Down syndrome results when abnormal cell division involving chromosome 21 occurs. These cell division abnormalities result in an extra partial or full chromosome 21. This extra genetic material is responsible for the characteristic features and developmental problems of Down syndrome. Any one of three genetic variations can cause Down syndrome:
· Trisomy 21. About 95 percent of the time, Down syndrome is caused by trisomy 21 — the person has three copies of chromosome 21, instead of the usual two copies, in all cells. This is caused by abnormal cell division during the development of the sperm cell or the egg cell.
· Mosaic Down syndrome. In this rare form of Down syndrome, a person has only some cells with an extra copy of chromosome 21. This mosaic of normal and abnormal cells is caused by abnormal cell division after fertilization.
· Translocation Down syndrome. Down syndrome can also occur when a portion of chromosome 21 becomes attached (translocated) onto another chromosome, before or at conception. These children have the usual two copies of chromosome 21, but they also have additional genetic material from chromosome 21 attached to another chromosome.
There are no known behavioral or environmental factors that cause Down syndrome.
Risk factors
Some parents have a greater risk of having a baby with Down syndrome. Risk factors include:
· Advancing maternal age. A woman's chances of giving birth to a child with Down syndrome increase with age because older eggs have a greater risk of improper chromosome division. A woman's risk of conceiving a child with Down syndrome increases after 35 years of age. However, most children with Down syndrome are born to women under age 35 because younger women have far more babies.
· Being carriers of the genetic translocation for Down syndrome. Both men and women can pass the genetic translocation for Down syndrome on to their children.
· Having had one child with Down syndrome. Parents who have one child with Down syndrome and parents who have a translocation themselves are at an increased risk of having another child with Down syndrome. A genetic counselor can help parents assess the risk of having a second child with Down syndrome.
5.3 Hydro cephaly
Hydrocephalus is a condition that occurs when fluid builds up in the skull and causes the brain to swell. The name means “water on the brain.”
Brain damage can occur as a result of the fluid buildup. This can lead to developmental, physical, and intellectual impairments. It requires treatment to prevent serious complications.
Hydrocephalus mainly occurs in children and adults over 60, but younger adults can get it too. The National Institute of Neurological Disorders and Stroke (NINDS) estimates that 1 to 2 of every 1,000 babies are born with hydrocephalus.
Cerebrospinal fluid (CSF) flows through your brain and spinal cord in normal conditions. Under certainconditions, the amount of CSF in your brain increases. The amount of CSF can increase when:
Too much of this fluid puts your brain under too much pressure. This pressure can cause brain swelling, which can damage your brain tissue.
In some cases, hydrocephalus starts before a baby is born. This can result from:
This condition can also occur in infants, toddlers, and older children due to:
When hydrocephalus occurs in adults, CSF levels rise but the amount of pressure is usually normal. It still causes the brain to swell and can lead to impaired functioning. In adults, this condition usually results from conditions that prevent CSF from flowing. However, in some cases, there is no known cause.
You might be at higher risk if you’ve experienced any of the following:
If you suspect that you or your child has hydrocephalus, your doctor will perform a physical exam to look for signs and symptoms. In children, doctors check for eyes that are sunken in, slow reflexes, a bulging fontanel, and a head circumference that is larger than normal for their age.
Your doctor may also use an ultrasound to get a closer look at the brain. These tests use high-frequency sound waves to create images of the brain. This type of ultrasound can only be done in babies whose fontanel (soft spot) is still open.
Magnetic resonance imaging (MRI) scans can be used to look for signs of excess CSF. MRIs use a magnetic field and radio waves to make a cross-sectional image of the brain.
Computerized tomography (CT) scans can also help diagnose hydrocephalus in children and adults. CT scans use several different X-rays to form a cross-sectional image of the brain. These scans can show enlarged brain ventricles that result from too much CSF.
Hydrocephalus can be fatal if it’s left untreated. Treatment may not reverse brain damage that’s already occurred. The goal is to prevent further brain damage. This involves restoring the normal flow of CSF. Your doctor may explore either of the following surgical options:
In most cases, a shunt is surgically inserted. The shunt is a drainage system made of a long tube with a valve. The valve helps CSF flow at a normal rate and in the right direction. Your doctor inserts one end of the tube in your brain and the other end into your chest or abdominal cavity. Excess fluid then drains from the brain and out the other end of the tube, where it can be more easily absorbed. A shunt implant is typically permanent and has to be monitored regularly.
A procedure called a ventriculostomy can be performed as an alternative to having a shunt inserted. This involves making a hole at the bottom of a ventricle or in between ventricles. This allows CSF to leave the brain.
5.4 Cretinism
Congenital hypothyroidism, previously known as cretinism, is a severe deficiency of thyroid hormone in newborns. It causes impaired neurological function, stunted growth, and physical deformities. The condition may occur because of a problem with the baby’s thyroid gland, or a lack of iodine in the mother’s body during pregnancy.
A baby’s body needs iodine to make thyroid hormones. These hormones are essential for healthy growth, brain, and nervous system development.
The introduction of iodized salt in the early 20th century made congenital hypothyroidism very rare in the United States and the rest of the Western world. However, severe iodine deficiency is still common in developing nations.
Congenital hypothyroidism vs. myxedema
Myxedema is a term used to describe a severely underactive thyroid gland in an adult. Congenital hypothyroidism refers to a thyroid deficiency in an infant.
Myxedema can also be used to describe skin changes caused by low thyroid hormone levels.
Signs of cretinism or congenital hypothyroidism in a newborn include:
Causes
Congenital hypothyroidism in newborns can be caused by:
Iodine deficiency is no longer considered a health risk in the United States due to the introduction of iodized salt. However, it’s still the most common preventable cause of impaired neurological function in the world.
Because our bodies don’t make iodine, we need to get it from food. Iodine gets into food through soil. In some parts of the world, the soil is lacking in iodine.
Newborns in the United States and many other countries are routinely screened for thyroid hormone levels. The test involves taking a small blood sample from the baby’s heel. A laboratory checks the baby’s blood levels of thyroid hormone (T4) and thyroid-stimulating hormone (TSH).
Doctors called pediatric endocrinologists treat congenital hypothyroidism. The main treatment is to give the baby thyroid hormone (levothyroxine). This condition must be treated within the first four weeks after birth or the intellectual disability may be permanent.
Thyroid hormone comes in a pill that parents can crush up into their baby’s breast milk, formula, or water. Parents need to be cautious about using some formulas. Soy protein and concentrated iron formulas can interfere with the absorption of thyroid hormone.
Once babies are on thyroid hormone medication, they will need to have blood tests every few months. These tests will check that their TSH and T4 levels are within a normal range.
Congenital hypothyroidism is typically seen in developing countries where iodine deficiency is common. Adults can prevent iodine deficiency by getting the Institute of Medicine’s recommended dietary allowance (RDA) of 150 micrograms of iodine per day. One teaspoon of iodized salt contains about 400 micrograms of iodine.
Because an iodine deficiency in pregnancy can be dangerous to the growing baby, pregnant women are advised to get 220 micrograms of iodine daily. The American Thyroid Association recommends that all women who are pregnant or breastfeeding take a prenatal vitamin containing at least 150 micrograms of iodine each day.
5.5 Progressive Metabolic Disorders
Metabolic syndrome is a cluster of conditions that occur together, increasing your risk of heart disease, stroke and type 2 diabetes. These conditions include increased blood pressure, high blood sugar, excess body fat around the waist, and abnormal cholesterol or triglyceride levels.
Having just one of these conditions doesn't mean you have metabolic syndrome. But it does mean you have a greater risk of serious disease. And if you develop more of these conditions, your risk of complications, such as type 2 diabetes and heart disease, rises even higher.
Most of the disorders associated with metabolic syndrome don't have obvious signs or symptoms. One sign that is visible is a large waist circumference. And if your blood sugar is high, you might notice the signs and symptoms of diabetes — such as increased thirst and urination, fatigue, and blurred vision.
Causes
Metabolic syndrome is closely linked to overweight or obesity and inactivity.
It's also linked to a condition called insulin resistance. Normally, your digestive system breaks down the foods you eat into sugar. Insulin is a hormone made by your pancreas that helps sugar enter your cells to be used as fuel.
In people with insulin resistance, cells don't respond normally to insulin and glucose can't enter the cells as easily. As a result, your blood sugar levels rise even as your body churns out more and more insulin to try to lower your blood sugar.
Risk factors
The following factors increase your chances of having metabolic syndrome:
· Age. Your risk of metabolic syndrome increases with age.
· Ethnicity. In the United States, Hispanics— especially Hispanic women — appear to be at the greatest risk of developing metabolic syndrome.
· Obesity. Carrying too much weight, especially in your abdomen, increases your risk of metabolic syndrome.
· Diabetes. You're more likely to have metabolic syndrome if you had diabetes during pregnancy (gestational diabetes) or if you have a family history of type 2 diabetes.
· Other diseases. Your risk of metabolic syndrome is higher if you've ever had nonalcoholic fatty liver disease, polycystic ovary syndrome or sleep apnea.
Complications
Having metabolic syndrome can increase your risk of developing:
· Type 2 diabetes. If you don't make lifestyle changes to control your excess weight, you may develop insulin resistance, which can cause your blood sugar levels to rise. Eventually, insulin resistance can lead to type 2 diabetes.
· Heart and blood vessel disease. High cholesterol and high blood pressure can contribute to the buildup of plaques in your arteries. These plaques can narrow and harden your arteries, which can lead to a heart attack or stroke.
Prevention
A lifelong commitment to a healthy lifestyle may prevent the conditions that cause metabolic syndrome. A healthy lifestyle includes:
· Getting at least 30 minutes of physical activity most days
· Eating plenty of vegetables, fruits, lean protein and whole grains
· Limiting saturated fat and salt in your diet
· Maintaining a healthy weight
· Not smoking