Down syndrome is a genetic condition that causes mental retardation and some specific physical characteristics. It was named after John Langdon Down, the 19^th century physician who first described it. The condition occurs in about one in every 800 newborns, according to the U.S. Centers for Disease Control and Prevention (CDC), and occurs equally among all races and ethnic groups.

Down syndrome is caused by the presence of an extra chromosome. Most cells in the human body have 46 chromosomes in 23 pairs. The mother and father each contribute one-half of each pair. However, people with Down syndrome have triplication of chromosome 21 (an extra copy or extra genetic material of the smallest of these chromosomes, chromosome 21) The cause of this chromosomal abnormality is not known. However, the risk of having a child with Down syndrome increases as a parent ages.

The characteristics, features and potential complications of Down syndrome vary greatly among patients. Down syndrome is commonly associated with a number of physical features, including a flat facial profile, upward slanting eyes and a single crease along the center of the palms. Various medical issues, including an increased susceptibility to infection, poor muscle tone, congenital heart defects and eye, ear, breathing and digestive problems, are also generally associated with Down syndrome.

The extra genetic material present in Down syndrome also results in developmental delays, including mild to moderate mental retardation. Infants born with Down syndrome are usually born an average size, but tend to grow more slowly than others. Because of this, most people with Down syndrome will be smaller than their age peers throughout life. Other developmental delays include delays in sitting up, walking, talking and toilet training. Early intervention with speech, physical and occupational therapy can help overcome these delays. Children and adolescents with Down syndrome may attend regular schools, although some may still need special classes to help with learning disabilities.

Down syndrome is often detected before birth. Prenatal screening tests may be used to determine the chance that a particular fetus has Down syndrome. A positive result on a screening test may lead to the use of a diagnostic test such as amniocentesis or chorionic villus sampling. Prenatal diagnosis of Down syndrome may give parents the time to decide to terminate the pregnancy or to adjust to the upcoming challenges of raising a child with Down syndrome. After an infant is born, Down syndrome can usually be diagnosed by a physical examination.

There is no cure for Down syndrome and no known way to prevent it. Though the condition itself cannot be treated, the health problems that are often associated with it can be.

Down syndrome is a condition caused by extra genetic material that results in some degree of mental retardation and certain physical problems. Usually, people with Down syndrome have an entire extra chromosome in most of their cells, although occasionally only an extra piece of a chromosome is present.

Down syndrome is among the most common birth defects and is the most common cause of developmental delays and mental retardation in the United States. The condition was named after John Langdon Down, the 19^th century physician who first described it. Down syndrome is associated with certain facial features (e.g., flatter face, upward slanting eyes) that may seem abnormal, particularly for the child’s race.

Most people have 46 chromosomes in 23 pairs in all of their cells -- 22 regular pairs and one pair of sex chromosomes. The mother and father each contribute one chromosome of each pair. However, people with Down syndrome have triplication of chromosome 21 (an extra copy in the smallest of these chromosome pairs, chromosome 21). This extra copy may be an entire extra chromosome, or only a part of it attached to a different chromosome.

This extra genetic material found in Down syndrome can affect almost every system in the body. It almost always results in developmental delays, including mild to moderate mental retardation. The severity of mental retardation and developmental delays in children with Down syndrome varies widely. Some have a near-normal overall level of functioning, but others require substantial assistance. However, people with Down syndrome tend to demonstrate near-average levels of social functioning. In general, a child's overall functioning can be improved with proper medical management, therapy, education and a supportive home environment.

About one in every 800 newborns has Down syndrome, according to the U.S. Centers for Disease Control and Prevention (CDC). The condition occurs equally among all races and ethnic groups.

Down syndrome involves an abnormality in chromosome 21. Each person has 23 pairs of chromosomes in each body cell -- 22 regular pairs and one pair of sex chromosomes. The abnormality associated with Down syndrome and chromosome 21 can occur three ways:

• Standard trisomy 21. Three entire copies of chromosome 21 occur in all the nonreproductive cells in a child's body. This form results from a problem that occurs during egg or sperm cell development. The vast majority of Down syndrome cases are of this type.
  
  
• Translocation 21. Due to an abnormality in the genes of a parent or an error in egg or sperm cell development, an extra piece of chromosome 21 is attached to a different chromosome. The normal pair of chromosome 21 is still present. This is an uncommon form of Down syndrome.
  
  
• Mosaic trisomy 21. Three entire copies of chromosome 21 occur in some, but not all, cells in the child's body. This is caused by a problem in embryo development after the sperm and egg have joined. It is a rare form of Down syndrome.

Infants with Down syndrome will generally require more frequent medical checkups (e.g., well-child visits) to ensure and maintain good health. Some symptoms that commonly affect infants with Down syndrome must be identified shortly after birth and monitored. For example, babies with heart or gastrointestinal defects may require corrective surgery in infancy.

Infants with Down syndrome are usually born an average size but tend to grow more slowly than others. Because of this, throughout life, most people with Down syndrome will be smaller than their age peers.

Down syndrome infants frequently have poor muscle tone (hypotonia). This may lead to problems with sucking and feeding. These infants develop more slowly than other infants. They tend to sit up and reach other developmental milestones later than usual. Teething often occurs later and the teeth may erupt in an abnormal pattern. Digestive issues such as constipation are also common during infancy.

Early intervention services can be extremely helpful for Down syndrome patients. These are best started as early as possible. Regular physical therapy, for example, can help to build muscle tone and improve coordination so the infants can learn to sit up and crawl.

Children with Down syndrome generally still require frequent medical checkups (e.g., well-child visits) to ensure and maintain good health. Many pediatricians recommend vision and hearing tests at every visit. Many children with Down syndrome have sight problems and suffer from chronic ear infections (e.g., otitis media) in addition to hearing loss, which can compromise their ability to learn and use language. Identifying vision and hearing problems early may minimize their effect on learning and language skills.

Developmental delays continue in childhood. Children with Down syndrome may begin to walk and speak later than other children. It may also take longer for them to become toilet trained and to learn to feed and dress themselves.

Early-intervention services are generally recommended to continue from infancy up to school age. Physical therapy can continue to help increase muscle tone and coordination. Occupational therapy can be used to improve fine-motor skills, such as hand coordination. Speech therapy may help to improve language development. Therapists can also teach the parents of children with Down syndrome how to continue to improve these and other communication skills at home.

The U.S. Individuals with Disabilities Education Act (IDEA) guarantees educational services to children with Down syndrome who are 3 years of age and older. This includes free education that is appropriate for the child's level of development and an individualized education plan (IEP). These services are typically provided by the local school district.

Many school-aged children with Down syndrome can attend classes in regular schools. Some may still need special classes to help with any learning disabilities. There are also special programs available for the schooling of children with Down syndrome.

Children with Down syndrome can participate in activities (e.g., music, dance) and usually play sports, although medical problems may restrict some of these children from certain sports (e.g., football, diving). Many children with Down syndrome participate in the Special Olympics, a sports training and athletic competition for people with intellectual disabilities.

Schooling for children with Down syndrome may vary by state and school district. In some areas, classrooms are grouped by age regardless of education level. In others, children with disabilities may study separately in groups according to their ability level. Parents of Down syndrome children can educate themselves about their child's abilities and the programs offered within their districts.

Many adolescents with Down syndrome can still attend the same classes and schools and participate in the same activities as their age peers. They can often get after-school or summer jobs. Some continue their education through college, and many can look forward to living at least partially independently.

These adolescents generally have the same desires and interests as other adolescents. They can be concerned over romantic relationships and having their own families one day. Boys and men with Down syndrome are usually infertile. Girls with Down syndrome reach sexual maturity and experience menstrual periods, and many can become pregnant. However, a girl or woman with Down syndrome has an increased chance of having a child who also has Down syndrome.

The characteristics, features and potential complications of Down syndrome vary greatly among patients. All children with the condition are different. However, some degree of mental retardation is nearly universal. In most cases, children with Down syndrome have mild to moderate retardation. Severe retardation is uncommon.

Mild retardation is defined as an intelligence quotient (IQ) of 50 to 70, moderate retardation as an IQ of 35 to 50, severe retardation as an IQ of 20 to 35. The overall development is slow in these children but still occurs. In most cases, children with Down syndrome reach all of the developmental goals of infancy and childhood, just not as quickly as usual.

Down syndrome is commonly associated with a number of physical features. Some children with the condition may have many of these. However, some may have few, if any. These physical features include:

• A small, short and broad head
  
  
• A flat facial profile with a flat nasal bridge
  
  
• Upward slanting eyes with epicanthic folds (eyelid folds at the inner corner of the eyes)
  
  
• Brushfield spots (speckled discoloration on the iris, the colored part of the eye)
  
  
• Small ears that may be misshapen or look lower than usual
  
  
• A small mouth with a large, protruding tongue
  
  
• Excess skin at the back of the neck
  
  
• Short, broad hands with short fingers
  
  
• A curved fifth finger
  
  
• Simian crease (single crease along the center of the palms)
  
  
• Wide gap between the big toe and the second toe

Many medical problems are commonly associated with Down syndrome. Some children with the condition have no other medical problems at all. However, others require a great deal of medical attention. Medical problems commonly associated with Down syndrome include:

• Infections. Most children with Down syndrome are at least slightly more susceptible to infections (e.g., colds, flu) that their peers. When these infections occur, they are likely to last longer than normal.
  
  
• Low muscle tone and loose joints. Many children with Down syndrome have low muscle tone (hypotonia) and loose joints. This can result in excessive flexibility and a floppy, rag-doll like appearance. These problems are often worse in infancy and improve with age. Children with Down syndrome have a 6 percent chance of dislocating their hip, according to the American Academy of Pediatrics (AAP). Some children have a characteristic instability with the bones in the neck that may need to be monitored.
  
  
• Ear problems. Hearing loss occurs in 75 percent of children with Down syndrome, according to the AAP. These children also have between a 50 and 75 percent risk of ear infections. These problems may be due to structural problems or a fluid buildup in the inner ear.
  
  
• Obstructive sleep apnea. Temporary interruptions in breathing during sleep. Children with Down syndrome have a 50 to 75 percent risk of sleep apnea, according to the AAP.
  
  
• Eye problems. The AAP reports an overall risk of eye disease of 60 percent in children with Down syndrome. This includes a 50 percent risk of vision loss due to severe myopia (nearsightedness), hyperopia (farsightedness) or astigmatism (abnormal shape of the retina). These children also have a 15 percent chance of cataracts, according to the AAP. Lazy eye (amblyopia) is also more common in children with Down syndrome.
  
  
• Congenital heart defects. According to the AAP, about 50 percent of infants with Down syndrome are born with heart defects, such as abnormal openings called septal defects. These conditions can also increase a child’s risk of high blood pressure in the lungs (pulmonary hypertension).
  
  
• Thyroid disease. Children with Down syndrome have a 15 percent risk of thyroid disease (e.g., hypothyroidism), according to the AAP.
  
  
• Digestive problems. The AAP reports that 12 percent of infants with Down syndrome are born with incomplete or absent openings (atresia) in their digestive tract. These can include the openings into and out of the stomach, between different parts of the intestines, or a lack of an anus. Poor muscle tone may also increase the risk of digestive problems such as constipation. Intestinal obstruction (blockage) may occur due to problems with function (Hirschsprung disease) in 1 percent of Down syndrome infants, according to the AAP. There may be an increased risk of celiac disease (gluten intolerance).
  
  
• Childhood leukemia. Children with Down syndrome have a greater risk of leukemia than other children. However, this risk is still low, less than 1 percent, according to the AAP. Furthermore, depending on the type of leukemia present, children with Down syndrome may have a higher long-term survival rate than other children with the same type of leukemia.
  
  
• Other problems, such as:
  
  
• • Obesity
    
  • Seizure disorders
    
  • Respiratory problems
    
  • Alopecia areata (patchy baldness)

Some of the developmental delays of Down syndrome may worsen the child’s experience with physical symptoms. For example, many children with Down syndrome have delayed or difficult to understand speech. They also understand language more readily than they can use it and may not be able to say when a body part hurts. They may refuse to walk on a hurt foot if they are unable to tell someone about the pain.

Down syndrome is often detected before birth. Prenatal testing includes screening tests and diagnostic tests. Screening tests identify a higher likelihood of a given defect but cannot definitively diagnose it. A woman who receives a positive result on a screening test may elect to have a diagnostic test, which can confirm the presence of Down syndrome in more than 98 percent of cases.

Prenatal screening tests include:

• Maternal blood tests. Identify and measure substances in the mother’s blood that reveal information about her fetus. There are a number of these tests available, including the triple screen test and quadruple screen test. The triple screen identifies the levels of alpha-fetoprotein (AFP), human chorionic gonadotropin (HCG) and estriol. The quadruple screen tests levels of those three elements plus the inhibin A protein. They are usually performed in the 16^th to 18^th weeks of pregnancy.
  
  
• Detailed ultrasound. Uses sound waves to create an image of inside a mother's womb. This can be used to identify certain physical features common in Down syndrome, but it is not very accurate without supplementation with other screening tests.
  
  
• Nuchal translucency testing. Ultrasound is used to examine the back of the fetus's neck. Fluid tends to accumulate in this area when Down syndrome or other chromosomal conditions are present. This gives a swollen appearance on the ultrasound. This test may be performed between 11 and 14 weeks of pregnancy. Recent research indicates that nuchal translucency testing combined with a test for HCG and another protein can identify more than 80 percent of Down syndrome cases before 13 weeks of gestation, much earlier than some diagnostic tests.

The American College of Obstetricians and Gynecologists began recommending in 2007 that all pregnant women be offered the choice of having screening tests for Down syndrome, not just higher-risk mothers.

Prenatal diagnostic tests are nearly 99 percent accurate in identifying Down syndrome and certain other chromosomal conditions, according to the American Academy of Family Physicians. However, they are associated with complications, including a risk of miscarriage and preterm labor. These tests are typically recommended only for women with a high risk of having a child with Down syndrome, including those over age 35, those with a family history of genetic problems and those who had abnormal results on screening tests.

Prenatal diagnostic tests include:

• Amniocentesis. A needle is inserted through the abdomen and into the uterus. Then, a small amount of amniotic fluid (the fluid in the uterus) is removed for testing. This test is generally performed between 16 and 20 weeks into the pregnancy.
  
  
• Chorionic villus sampling (CVS). A sample of the placenta is removed for testing. It may be obtained using either a needle through the abdomen (as in amniocentesis) or a tube inserted through the vagina. This test can be performed between eight and 12 weeks of pregnancy.
  
  
• Percutaneous umbilical blood sampling (PUBS). A needle is used to remove a sample of blood from the fetus's umbilical cord. This test carries higher risks of complications than amniocentesis or CVS and is typically used only when diagnosis must be made quickly. It is typically performed later in pregnancy, after 20 weeks.

The results of screening and diagnostic tests may provide pregnant women with valuable information about the fetus. Some women may choose to terminate an affected pregnancy. Others use the information to prepare to care for an infant with special needs.

After an infant has been born, Down syndrome can usually be diagnosed by a physical examination, or even just looking at the infant. The diagnosis is confirmed with a karyotype. This is a chart of the child's chromosomes created using a blood or other tissue sample.

There is no cure for Down syndrome, but the health problems that are often associated with it can be treated.

At one time, death in infancy or childhood was nearly universal for Down syndrome patients. Now, most children born with Down syndrome survive into older adulthood, as a result of better understanding of the condition and medical advances such as antibiotics and corrective surgery. However, they do require more frequent medical checkups (e.g., well-child visits) than normal, including regular eye and ear examinations.

The birth defects that may be associated with Down syndrome (e.g., heart defects, gastrointestinal atresia) can typically be treated through surgery. After these abnormalities are corrected, they usually cause no more problems. Infections (e.g., colds, ear infections) and other conditions (e.g., thyroid disease, seizure disorders) can be treated with medications. Vision or hearing loss may require corrective lenses or hearing aids. Obstructive sleep apnea (temporary interruptions in breathing while asleep) can often be treated with a tonsillectomy (surgical removal of the tonsils) or adenoidectomy (surgical removal of the adenoids). As with all children, proper nutrition and regular physical activity are also very important to maintain good health.

The developmental problems associated with Down syndrome are a lifelong concern. Parents may involve themselves in their children's treatment, therapy and education so the children can achieve to the limits of their abilities in independent living and functioning.

There is no sure way to prevent Down syndrome, but women and men can increase their chances of having healthy children by not delaying parenthood until later in life.

Preparing questions in advance can help patients and parents have more meaningful discussions with their physicians regarding their or their child's treatment options. The following questions about Down syndrome may be helpful:

1. Do you know of any support groups in the area where I can meet and talk to children with Down syndrome and their parents?
   
   
2. What type of Down syndrome does my child have?
   
   
3. Does my child have any complications associated with Down syndrome, such as heart or intestinal defects?
   
   
4. What treatments do you recommend for my child's complications?
   
   
5. How frequently should my child come in for regular checkups?
   
   
6. What signs and symptoms of infections should I watch for in my child?
   
   
7. How will I know if my child is in pain if there are communication problems?
   
   
8. Are there any signs I should be on the lookout for that may indicate that my child may be losing vision or hearing?
   
   
9. What early intervention services for children with Down syndrome are available in my area?
   
   
10. Do you recommend that my child attend a regular school or a special school for children with Down syndrome?
    
    
11. What are the risks that any additional children I may have will also have Down syndrome?