Down Syndrome : Genetic Disorder of Humans
Down syndrome (DS) is a chromosomal disorder that includes a combination of birth defects, including some degree of mental retardation, characteristic facial features and, often, heart defects and other health problems. The severity of these problems varies greatly among affected individuals.
- What are Chromosomal Abnormalities
- What are Gene Families and How they Evolved?
- What are interrupted Genes
How often the syndrome occurs?
Down syndrome is one of the most common genetic defects birth and affects about one in 800 babies (about 3,400 infants) each year in the United States. According to the National Down Syndrome Society (National Down Syndrome Society), in the US There are more than 400,000 individuals with Down syndrome.
What are the causes of Down syndrome?
Down syndrome is caused by the presence of extra genetic material from chromosome 21. Chromosomes are the cell structures containing the genes. Normally, each person has 23 pairs of chromosomes or 46 in total. Every individual inherits one chromosome from each pair of the egg of the mother; inherits the other chromosome of each pair from the father’s sperm. In normal situations, the union of egg and sperm results in a fertilized egg with 46 chromosomes.
Sometimes something goes wrong before fertilization. An egg or sperm development can be divided incorrectly and produce an egg or sperm with an extra chromosome 21. When sperm meets an egg, the resulting embryo has 47 chromosomes instead of 46. Down syndrome is called trisomy 21 because affected individuals have three chromosomes 21 instead of two. This type of accident in cell division produces about 95 percent of cases of Down syndrome.
Occasionally, before fertilization, part of chromosome 21 is released during cell division and attaches to another chromosome in the egg or sperm. The resulting embryo may have what is called “translocation Down syndrome“. Affected people have two normal copies of chromosome 21, and chromosome 21 additional material attached to another chromosome. This type of accident in cell division is responsible for about 3 to 4 percent of cases of Down syndrome. In some cases, the parent has a redistribution of chromosome 21, called balanced translocation, it does not affect health.
- What is Mendelian Law and Mendelism?
- Types of DNA
About 1 to 2 percent of people have a form of Down syndrome called mosaic Down syndrome. 3 In this case, the accident in cell division occurs after fertilization. Affected individuals have some cells with an extra chromosome 21 and others with the normal number.
What can health problems have people with Down syndrome?
The outlook for people with DS is more encouraging than they used to be. Most of the health problems associated with Down syndrome can be treated and life expectancy is currently 60 years. 2 People with Down syndrome are more likely than not to have affected one or more of the following diseases:
- Heart defects: About half of babies with D.Syndrome have heart defects. Some defects are minor and can be treated with drugs, but others require surgery. All babies with Down syndrome should be examined by a pediatric cardiologist, a doctor who specializes in heart diseases of children, and an echocardiogram (a special heart ultrasound) performed during the first two months of life to allow Treatment of any heart defect they may have.
- Intestinal defects: About 12 percent of babies with Down syndrome are born with intestinal malformations that have to be surgically corrected.
- Vision problems: More than 60 percent of children with Down syndrome have vision problems such as esotropia (cross-vision), myopia, hyperopia, and cataracts. The view can be improved with the use of glasses, surgery or other treatments. Children with Down syndrome should be examined by a pediatric ophthalmologist within the first 6 months of life and eye exams performed regularly.
- Hearing loss: Approximately 75 percent of children with Down syndrome have hearing impairments. It may be due to the presence of fluid in the middle ear (which may be temporary), defects in the middle or inner ear, or both things. Babies with Down syndrome should undergo tests at birth and again during the first months of life to detect hearing loss. Also, they should undergo hearing tests periodically to allow treatment of any problem and avoid problems in the development of speech and other skills.
- Infections: Children with Down syndrome tend to colds much and ear infections; moreover, often getting bronchitis and pneumonia. These children should receive all routine childhood vaccines that help prevent some of these infections.
- Thyroid problems: About 1 percent of babies with Down syndrome are born with congenital hypothyroidism, a thyroid hormone deficiency that can affect growth and brain development. This hypothyroidism can be detected by screening tests in routine newborn and treated oral doses of thyroid hormone. Children with Down syndrome are also at increased risk for thyroid problems and should be tested annually.
- Leukemia: Less than one in 100 children with Down syndrome develop leukemia, a cancer of the blood. Often, affected children can be successfully treated with chemotherapy.
- Memory loss: People with D.Syndrome are more likely than unaffected individuals to develop Alzheimer’s disease, characterized by gradual memory loss, personality changes and other problems) Adults with Down syndrome tend to develop Alzheimer’s disease rather than unaffected individuals. Studies suggest that about 25 percent of adults with Down syndrome over age 35 have symptoms of Alzheimer’s disease.
Some people with Down syndrome have several of these problems while others have none. The seriousness of the problems varies greatly.
What aspect has a child with Down syndrome?
A child with Down syndrome may have:
- Eyes slanted upward
- Small and slightly bent at the top of ear
- Smallmouth, making the tongue appear large
- Small flat nose and between the eyes
- Short neck
- Small hands and feet
- Low muscle tone
- Short stature in childhood and adulthood.
Most children with Down syndrome have some of these features, but not all.
How serious is an intellectual disability?
The degree of intellectual disability varies considerably. In most of those affected, intellectual disabilities are mild to moderate and, with proper intervention, few suffer severe intellectual disabilities. There is no way to predict the mental development of a child with Down syndrome based their physical characteristics.
What can a child with Down syndrome?
Usually, children with Down syndrome can do most of the things that makes any child, like walking, talking, dressing and going to the bathroom. However, generally, they start learning these skills later than unaffected children. You cannot predict the exact age when they reach these points of development. However, early intervention programs that begin in infancy can help these children overcome before the various stages of its development.
Can a child with Down syndrome go to school?
Yes. There are special programs from preschool to help children with Down syndrome develop skills as much as possible. Along with benefiting from early intervention and special education, many children get integrated into normal classes for children. Many affected children learn to read and write. Some finish high school and continue studying or go to college.
Many children with Down syndrome participate in various activities of the children, both at school and in their neighborhoods.While there are special work programs designed for adults with Down syndrome, many people affected by this disorder are able to work normally. Today, it is increasing the number of adults with Down syndrome living in a semi-independent in community group homes, take care of themselves, participate in household chores, make friends, take part in recreational activities and work in their community.
Can you cure Down syndrome?
There is no cure for Down syndrome. However, some studies suggest that women who have certain versions of some genes that affect the way your body metabolizes (process) the B vitamin folic acid may be more likely to have a baby with Down syndrome, If confirmed, this finding may provide yet another reason to recommend that women who may become pregnant to take a daily multivitamin containing 400 micrograms of folic acid. As has been proven, it helps to reduce the risk of having a baby with certain birth defects of the brain and spinal cord.
Does the risk of Down syndrome increase with maternal age?
Yes. The risk of Down syndrome increases with maternal age: 7
- At age 25, the probability that a woman teenager a baby with Down syndrome is 1 in 1,250.
- At age 30, the probability is 1 in 1,000.
- At 35 years, the probability is 1 in 400.
- At age 40, the probability is 1 in 100.
- At age 45, the probability is 1 in 30.
Although the risk is greater with increasing age of the mother, about 80 percent of babies with Down syndrome are born to women under 35 years. This is because younger women have more babies than older women.
What is the risk of parents of a child with Down syndrome having another affected child?
Overall, the chances of conceiving another baby with D.Syndrome in each subsequent pregnancy are 1 percent to 40 years. After 40 years, the risk varies depending on the age of the made. However, if the first child has translocation Down syndrome, the chance of having another child with Down syndrome may be greatly increased.
Usually, after birth, when you suspect that a baby has Down syndrome, the doctor draws a blood sample to perform a chromosomal analysis (called a karyotype). This analysis is used to determine if the baby has Down syndrome and to identify the corresponding genetic form. This information is important in determining the risk to parents in future pregnancies. The physician may refer parents to a genetic counselor to explain to them in detail the results of chromosomal analysis and tells them about the risks that this phenomenon is repeated in another pregnancy.
How to diagnose Down syndrome before birth?
Yes. The College of Obstetricians and Gynecologists in the United States (American College of Obstetricians and Gynecologists, ACOG) recommends offering all pregnant women, regardless of age, a screening test called prenatal testing in the first quarter. The test may consist of an analysis of the blood of the mother during the first trimester (11-13 weeks of pregnancy) with an exam ultrasound special (nuchal translucency), to measure the thickness of the baby’s neck. Or you can make an analysis of maternal blood during the second trimester (weeks 15-20) without ultrasound. The screening tests help identify pregnancies at risk for Down syndrome above average but not they can diagnose this or other birth defects.
Women who have an abnormal test result diagnostic testing can be performed as an amniocentesis or chorionic villus sample (CVS). These tests are used to diagnose or, more often, rule out Down syndrome with great accuracy.
ACOG also recommends that pregnant women of all ages have the option not to have the screening test but made directly to a diagnostic test for Down syndrome. 9 Until recently, only offered diagnostic tests rather than tests early detection, women over 35 years old and other women who were considered at increased risk of having a baby with Down syndrome as amniocentesis and CVS carry a small risk of spontaneous abortion. In the future, it is possible that screening tests for Down syndrome can be made by a simple blood test for pregnant women can detect and examine minute quantities of genetic material of the fetus.
Most parents received the news that the baby has Down syndrome which reassures. However, if prenatal diagnosis test shows that the baby has Down syndrome; parents have the opportunity to consider the diagnosis and options. They can also prepare medical, emotional and financial support for the birth of a child with special needs and program delivery in a properly equipped medical center.
Can people with Down syndrome have children?
While there have been rare exceptions, men with Down syndrome usually cannot father children. 3A woman with Down syndrome has a 50 percent chance of conceiving a child with Down syndrome but often occur in spontaneous abortions many pregnancies of an affected fetus.
Are you investigating the March of Dimes Down syndrome?
Yes. Some scholars of March of Dimes is investigating why accidents occur in the division of chromosomes in order to prevent Down syndrome and other birth defects caused by abnormalities in the number or structure of chromosomes. Other scholars are investigating the role specific genes in brain abnormalities and other health problems associated with Down syndrome, in order to develop appropriate treatments. One grantee, for example, is studying the role of genes in a form of leukemia that occurs in children with Down syndrome. Another is investigating the role of genes in causing premature Alzheimer’s disease in adults with Down syndrome. An international team of scientists has made a map of all the genes of chromosome 21, which could pave the way for finding a treatment for many of the characteristics of this disorder.
Where can you get more families affected by Down syndrome?
There are many organizations that provide support and information to families with children with Down syndrome, such as:
- Centres for Disease Control and Prevention (CDC). Down Syndrome. Created March 11, 2009, www.cdc.gov/ncbddd/birthdefects/Down Syndrome.htm.
- National Down syndrome Society. Information Topics. Retrieved April 20, 2009, www.ndss.org.
- American Academy of Pediatrics Committee on Genetics. Health Supervision for Children with Down syndrome. Pediatrics, Volume 107, Number 2, February 2001, pp. 442-449 (confirmed September 1, 2007).
- National Institute of Child Health and Human Development (NICHD). Facts About Down Syndrome. Last updated August 15, 2008, http://www.nichd.nih.gov/publications/pubs/downsyndrome.cfm.
- O’Leary, VB, et al. MTRR and MTHFR Polymorphism: Link to Down syndrome? American Journal of Medical Genetics, January 15, 2002, Volume 107, No. 2, pp. 151-155.
- Scala, I., et al. Analysis of Maternal Seven Polymorphisms of Genes Involved in Homocysteine / Folate Metabolism and Risk of Down syndrome. Genetics in Medicine, Volume 8, Number 7, July 2006, pp. 409-416.
- American College of Obstetricians and Gynecologists (ACOG). Your Pregnancy and Birth, Fourth Edition. ACOG, Washington, DC, 2005.
- Morris, JK, and Alberman, E. Recurrence of Free Trisomy 21: Analysis of Data from National Down syndrome Cytogenetic Register. Prenatal Diagnosis, Volume 25, Number 12, December 2005, pp. 1120-1128.
- American College of Obstetricians and Gynecologists (ACOG). Screening for Fetal Chromosomal Abnormalities. ACOG Practice Bulletin, number 77, January 2007.