The presence of three copies of chromosome 21 due to meiotic nondisjunction, Robertsonian translocation, or Down mosaicism.
The failure of chromosome pairs to separate properly during meiosis 1 and 2.
Significantly impaired cognitive functioning and deficits in two or more adaptive behaviors.
A simian crease is a single line that runs across the palm of the hand.
Patients with Down syndrome have characteristically flat facies consisting of a low nasal bridge and small nose.
Duodenal atresia is a birth defect of the digestive tract where the duodenum is not patent. This occurs more frequently in infants with Down syndrome. Duodenal atresia is commonly diagnosed with a “double bubble” sign on imaging.
This disease is characterized by the loss of Auerbach's plexus in the gut, causing failure of a segment of the colon to relax. Hirschsprung's disease is more common in individuals with Down syndrome.
While the majority of atrial septal defects are septum secundum type, Down syndrome is most commonly associated with a septum primum type ASD.
A range of congenital cardiac defects characterized by involvement of the atrial septum, the ventricular septum, and one or both of the AV valves.
Prominent skin fold of the upper eyelid, covering the inner corner medial canthus, is common in Down syndrome.
Children with Down syndrome have a markedly increased risk for acute lymphoblastic leukemia.
People with Down syndrome begin to have symptoms of Alzheimer's disease in their late 40s or early 50s. Although the exact cause is unknown, the early onset of Alzheimer's may be linked to the extra copy of chromosome 21, because it can lead to increased production of beta amyloid in the brain.
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