Down syndrome can result from several different genetic mechanisms. This results in a wide variability in individual signs and symptoms due to complex gene and environment interactions.
Prior to birth, it is not possible to predict the symptoms that an individual with Down syndrome will develop.
Individuals with Down syndrome may have some or all of the following physical characteristics: microgenia (abnormally small chin), oblique eye fissures with epicanthic skin folds on the inner corner of the eyes (formerly known as a mongoloid fold), muscle hypotonia (poor muscle tone), a flat nasal bridge, a single palmar fold, a protruding tongue (due to small oral cavity, and an enlarged tongue near the tonsils) or macroglossia, excessive joint laxity including atlanto-axial instability, excessive space between large toe and second toe, a single flexion furrow of the fifth finger, and a higher number of ulnar loop dermatoglyphs.
Most individuals with Down syndrome have intellectual disability in the mild (IQ 50–70) to moderate (IQ 35–50) range, with individuals having Mosaic Down syndrome typically 10–30 points higher.
They also may have a broad head and a very round face.
Language skills show a difference between understanding speech and expressing speech, and commonly individuals with Down syndrome have a speech delay. Fine motor skills are delayed and often lag behind gross motor skills and can interfere with cognitive development.
Effects of the condition on the development of gross motor skills are quite variable. Some children will begin walking at around 2 years of age, while others will not walk until age 4.
Physical therapy, and/or participation in a program of adapted physical education (APE), may promote enhanced development of gross motor skills in Down syndrome children.
Growth parameters such as height, weight, and head circumference are smaller in children with DS than with typical individuals of the same age.
Adults with DS tend to have short stature — the average height for men is 5 feet 1 inch (157 cm) and for women is four feet 9 inches (144 cm).
Individuals with DS are also at increased risk for obesity as they age.
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