Down syndrome

People with Down syndrome may develop the following medical problems:^[2] 

• Congenital hypothyroidism
• Hearing loss
• Congenital heart defects
• Seizures
• Vision disorders
• Decreased muscle tone (hypotonia)

Children with Down syndrome are also more likely to develop chronic respiratory infections, middle ear infections, and recurrent tonsillitis. In addition, there is a higher incidence of pneumonia in children with Down syndrome than in the general population.^[2]

Children with Down syndrome have developmental delay. They are often slow to turn over, sit, and stand. Developmental delay may be related to the child's weak muscle tone. Development of speech and language may also take longer than expected. Children with Down syndrome may take longer than other children to reach their developmental milestones, but many of these milestones will eventually be met.^[2]

Adults with Down syndrome have an increased risk of developing Alzheimer disease, a brain disorder that results in a gradual loss of memory, judgment, and ability to function. Although Alzheimer disease is usually a disorder that occurs in older adults, about half of adults with Down syndrome develop this condition by age 50.^[2]

There are 3 possible genetic causes of Down syndrome:^[2][3][5]

• Trisomy 21. Most often, Down syndrome is caused by an extra chromosome 21 in all cells of the affected person.  In these cases, the chromosome 21 pair fails to separate during the formation of an egg (or sperm); this is called "nondisjunction." When the egg with 2 copies of chromosome 21 unites with a normal sperm with one copy of chromosome 21 to form an embryo, the resulting embryo has 3 copies of chromosome 21 instead of the normal two.The extra chromosome is then copied in every cell of the baby's body, causing the features of Down syndrome.
  
  The cause of nondisjunction is unknown, but research has shown that it happens more often as women age. Nondisjunction is not known to be caused by anything in the environment or anything that parents do (or don't do) before or during pregnancy.

• Mosaic trisomy 21. In about 1-2% of cases, only some of the cells in a person's body have an extra chromosome 21; this is called "mosaic trisomy 21".  In this situation, the fertilized egg may have the right number of chromosomes, but due to a cell division error early in the development of the embryo, some cells "acquire" an extra chromosome 21. A person with mosaic trisomy 21 typically has 46 chromosomes in some cells, and 47 chromosomes (with the extra chromosome 21) in others. The features and severity in people with mosaic trisomy 21 may vary widely.

• Translocation trisomy 21. About 3-4% of people with Down syndrome have cells that contain 46 chromosomes; however, there is extra chromosome 21 material attached (translocated) onto another chromosome. For parents of a child with Down syndrome due to a translocation, there may be an increased chance of Down syndrome in future pregnancies. This is because one of the two parents may be a carrier of a balanced translocation. However, not all parents of people with translocation trisomy 21 have a translocation.
  
  

Down syndrome may be suspected and/or diagnosed during pregnancy, or after a child is born.

During pregnancy, a woman can opt to have specific tests that may either screen for, or diagnosis, Down syndrome in a fetus. A screening test poses no risks to the fetus and can determine the likelihood that a fetus has Down syndrome. It may show that a fetus is at an increased risk to be affected, but cannot determine whether it is definitely affected. Screening tests for Down syndrome may involve different types of blood tests for the mother and/or specific types of ultrasounds that can detect features more common in fetuses with Down syndrome (called markers). Depending on the type of screening tests a woman has, they may be done during the 1st trimester, the 2nd trimester, or both. If a screening test shows an increased risk for Down syndrome, a woman may then choose to have a diagnostic test.^[7]

Diagnostic tests during pregnancy can determine with certainty whether a fetus has Down syndrome, but they are invasive and carry a slight risk of miscarriage. Examples of diagnostic tests include chorionic villus sampling in the 1st trimester and amniocentesis in the 2nd trimester. During these tests, a small sample of genetic material is obtained from the amniotic fluid or placenta, and the fetus' chromosomes are then analyzed in a laboratory.^[7]

In recent years, non-invasive prenatal testing (NIPT) has become available to women who are at increased risk to have a baby with Down syndrome. NIPT is a blood test that examines DNA from the fetus in the mother's bloodstream. However, women who have a positive NIPT result should then have invasive diagnostic testing to confirm the result.

People with questions about the different options for prenatal screening or diagnostic testing should speak with a genetic counselor. A genetic counselor can discuss the benefits, limitations and risks of each test, and help each person decide which test (if any) is best for them.

If a diagnosis of Down syndrome is not made prenatally, the diagnosis can be made in the newborn. Down syndrome may be suspected if a newborn has characteristic physical features of the condition. The diagnosis can then be confirmed by obtaining a karyotype (a blood test to look at a picture of the newborn's chromosomes).^[8]

Early intervention services, quality educational programs, a stimulating home environment, good health care, and positive support from family and friends can help people with Down syndrome develop to their full potential.^[6] The overall goal of treatment is to boost cognition by improving learning, memory, and speech.^[9] Other treatments depend on the specific health problems or complications present in each affected person. The Research Down syndrome Foundation have a webpage with information about active reseach projects.