These cell division abnormalities result in an extra partial or full chromosome 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:. Most of the time, Down syndrome isn't inherited. It's caused by a mistake in cell division during early development of the fetus. Translocation Down syndrome can be passed from parent to child.
However, only about 3 to 4 percent of children with Down syndrome have translocation and only some of them inherited it from one of their parents. When balanced translocations are inherited, the mother or father has some rearranged genetic material from chromosome 21 on another chromosome, but no extra genetic material.
This means he or she has no signs or symptoms of Down syndrome, but can pass an unbalanced translocation on to children, causing Down syndrome in the children. People with Down syndrome can have a variety of complications, some of which become more prominent as they get older. These complications can include:. For people with Down syndrome, getting routine medical care and treating issues when needed can help with maintaining a healthy lifestyle.
Life spans have increased dramatically for people with Down syndrome. Today, someone with Down syndrome can expect to live more than 60 years, depending on the severity of health problems. There's no way to prevent Down syndrome. If you're at high risk of having a child with Down syndrome or you already have one child with Down syndrome, you may want to consult a genetic counselor before becoming pregnant.
A genetic counselor can help you understand your chances of having a child with Down syndrome. He or she can also explain the prenatal tests that are available and help explain the pros and cons of testing. Mayo Clinic does not endorse companies or products. Advertising revenue supports our not-for-profit mission. This content does not have an English version. This content does not have an Arabic version. Overview The genetic basis of Down syndrome Open pop-up dialog box Close.
The genetic basis of Down syndrome There are 23 pairs of chromosomes, for a total of Request an Appointment at Mayo Clinic. Share on: Facebook Twitter. Prominent lower lip. Enlarged colon lacking nerve cells.
Absent anus. Clouding of the lens of the eye. Cloudy lens. Conductive deafness. Conductive hearing loss. Abnormal gait. Abnormal walk. Impaired gait. Underactive thyroid. Decreased pain sensation. Close sighted. Near sighted. Near sightedness. Squint eyes. Noninsulin-dependent diabetes. Type 2 diabetes. Type II diabetes. Late-onset form of familial Alzheimer disease. Broad hand. Broad hands. Wide palm. Zygomatic flattening.
Small ears. Underdeveloped ears. Short middle bone of the little finger. Short middle bone of the pinkie finger. Short middle bone of the pinky finger. Decreased body height. Small stature. No previous family history. Do you have more information about symptoms of this disease? We want to hear from you. Do you have updated information on this disease? Cause Cause. There are 3 possible genetic causes of Down syndrome : [2] [3] [5] Trisomy 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. 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 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 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 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. Regardless of the type of Down syndrome a person has, all people with Down syndrome have an extra, critical portion of chromosome 21 present in all or some of their cells.
This extra genetic material disrupts the normal course of development, causing the characteristic features of Down syndrome. Diagnosis Diagnosis. 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.
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. 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.
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. Treatment Treatment. 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. The Research Down syndrome Foundation have a webpage with information about active reseach projects.
Committee on Genetics. J Pediatr Health Care. Find a Specialist Find a Specialist. Healthcare Resources To find a medical professional who specializes in genetics, you can ask your doctor for a referral or you can search for one yourself. You can also learn more about genetic consultations from MedlinePlus Genetics. Related Diseases Related Diseases. Conditions with similar signs and symptoms from Orphanet. Differential diagnosis includes Zellweger syndrome, 9qter deletion or other chromosomal abnormalities.
Visit the Orphanet disease page for more information. Research Research. Clinical Research Resources ClinicalTrials. Click on the link to go to ClinicalTrials. Please note: Studies listed on the ClinicalTrials. We strongly recommend that you talk with a trusted healthcare provider before choosing to participate in any clinical study.
Patient Registry A registry supports research by collecting of information about patients that share something in common, such as being diagnosed with Down syndrome. The type of data collected can vary from registry to registry and is based on the goals and purpose of that registry.
Some registries collect contact information while others collect more detailed medical information. Learn more about registries. Organizations Organizations. Organizations Supporting this Disease. Association for Children with Down Syndrome, Inc.
Do you know of an organization? Living With Living With. Their Web site offers general and condition-specific education resources to help teachers and parents better understand the needs of students who have genetic conditions.
Still, many physicians are not fully informed about advising their patients about the incidences of Down syndrome, advancements in diagnosis, and the protocols for care and treatment of babies born with Down syndrome.
Heredity is not a factor in trisomy 21 nondisjunction and mosaicism. Most cases are sporadic — chance — events. However, in about one-third of cases, one parent is a carrier of a translocated chromosome. Once a woman has given birth to a baby with trisomy 21 nondisjunction or translocation, it is estimated that her chances of having another baby with trisomy 21 is 1 in up until age Genetic counseling can determine the origin of translocation.
There are two categories of tests for Down syndrome that can be performed before a baby is born: screening tests and diagnostic tests. Prenatal screens estimate the chance of the fetus having Down syndrome. These tests do not tell you for sure whether your fetus has Down syndrome; they only provide a probability. There is an extensive menu of prenatal screening tests now available for pregnant women.
Most screening tests involve a blood test and an ultrasound sonogram. The blood tests or serum screening tests measure quantities of various substances in the blood of the mother. New advanced prenatal screens are now able to detect chromosomal material from the fetus that is circulating in the maternal blood. These tests are not invasive like the diagnostic tests below , but they provide a high accuracy rate.
Still, all of these screens will not definitively diagnose Down syndrome. Prenatal screening and diagnostic tests are now routinely offered to women of all ages.
The diagnostic procedures available for prenatal diagnosis of Down syndrome are chorionic villus sampling CVS and amniocentesis. Amniocentesis is usually performed in the second trimester between 15 and 20 weeks of gestation, CVS in the first trimester between 9 and 14 weeks.
Down syndrome is usually identified at birth by the presence of certain physical traits: low muscle tone, a single deep crease across the palm of the hand, a slightly flattened facial profile and an upward slant to the eyes. Because these features may be present in babies without Down syndrome, a chromosomal analysis called a karyotype is done to confirm the diagnosis. They photograph the chromosomes and then group them by size, number, and shape.
By examining the karyotype, doctors can diagnose Down syndrome. Another genetic test called FISH can apply similar principles and confirm a diagnosis in a shorter amount of time. Individuals with Down syndrome are becoming increasingly integrated into society and community organizations, such as school, health care systems, work forces, and social and recreational activities.
Individuals with Down syndrome possess varying degrees of cognitive delays, from very mild to severe. Most people with Down syndrome have cognitive delays that are mild to moderate. Due to advances in medical technology, individuals with Down syndrome are living longer than ever before.
In , children with Down syndrome were expected to survive to age nine. With the discovery of antibiotics, the average survival age increased to 19 or More and more Americans are interacting with individuals with Down syndrome, increasing the need for widespread public education and acceptance.
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