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Any one of three genetic changes can cause Down syndrome: Trisomy 21. About 95% of the time, Down syndrome is caused by trisomy 21. This means the person has three copies of chromosome 21, instead of the usual two copies. The extra chromosome 21 is in all cells in the body.
Trisomy 21 is the most common type of Down syndrome. The term “ trisomy ” means having an extra copy of a chromosome. Trisomy 21 occurs when a developing fetus has three copies of chromosome 21 in every cell instead of the typical two copies. This type makes up 95% of all cases of Down syndrome.
Signs and symptoms. Symptoms of Down syndrome may include: Distinctive facial features. Mild to moderate intellectual disabilities. Heart, kidney and thyroid issues. Numerous respiratory infections, from colds to bronchitis and pneumonia. Skeletal abnormalities, including spine, hip, foot and hand disorders.
Down syndrome (trisomy 21) is a genetic disorder that affects about one in 700 newborns. Often, people with Down syndrome look the same or related due to distinctive physical characteristics. This article explains Down syndrome and how it is diagnosed.
Trisomy 21. With Trisomy 21, each cell in the body has three separate copies of chromosome 21. About 95% of people with Down syndrome have Trisomy 21. Translocation Down syndrome. In this type, an extra part or a whole extra chromosome 21 is present.
13 min read. What Is Down Syndrome? Down syndrome is a genetic condition that causes mild to significant physical and developmental problems. People with Down syndrome (DS) are born with an...
Down Syndrome (Trisomy 21) - Learn about the causes, symptoms, diagnosis & treatment from the Merck Manuals - Medical Consumer Version.