Among the more common physical features are hypotonia (floppiness), small head with brachycephaly, epicanthic folds across the inside corners of the eyes, upward outward slanting palpebral fissures (eye slits), Brushfield spots in the iris, small mouth, small ears, excessive skin at the nape of the neck, a single transverse palmar crease, and short fifth finger with clinodactyly (incurving). A wide space, often with a deep fissure between the first and second toes, is also common.
There is an increased risk of congenital heart defects (50%); leukemia (<1%); hearing loss (75%); otitis media (ear infections) (50%-70%); Hirschsprung disease with absence of nerves from the bowel (<1%); gastrointestinal atresia (12%); eye disease (60%), including cataracts (15%) and severe refractive errors (50%); acquired hip dislocation (6%); obstructive sleep apnea (50%-75%); and thyroid disease (15%). There is no increased risk of solid tumors.
There is mental impairment. The degree is variable, ranging from mild (IQ: 50-70) to moderate (IQ: 35-50), and only occasionally to severe (IQ: 20-35).
The social quotient may be improved with early intervention techniques, although the level of function is exceedingly variable. Children with Down syndrome often function better in social situations than might be expected from their IQ.