Most common genetic cause of cognitive or intellectual disability, with a prevalence of 1 in 691 births.
Characteristic physical features include brachycephaly with a flat occiput; epicanthal folds and upslanting palpebral fissures; Brushfield spots in the iris; low nasal bridge; low-set ears; broad neck; and small hands with transverse crease.
Higher frequency of congenital and acquired medical conditions, including congenital heart defects, audiological, vision, GI, haematological, and thyroid issues.
Global developmental delay, variable IQ ranging from mild to moderate intellectual disability, and age-related pattern of neurobehavioural phenotype.
Early interventional therapies (e.g., speech therapy, physiotherapy, occupational therapy) and individualised educational programmes/resources are essential to maximise the potential of a person with Down's syndrome.
Down's syndrome (DS), or trisomy 21, is the most common genetic form of intellectual disability, occurring in 1 in 691 births.  In addition to having characteristic physical features, short stature, and hypotonia, individuals with DS have a distinctive cognitive and behavioural profile. They also have a higher frequency of associated medical conditions, including congenital heart defects, and gastrointestinal, thyroid, haematological, audiological, and visual abnormalities.
Associate Professor of Pediatrics
Down Syndrome Center of Western Pennsylvania
Children’s Hospital of Pittsburgh
KV declares that he has no competing interests.
Dr Kishore Vellody would like to gratefully acknowledge Dr Jeannie Visootsak, the previous contributor to this monograph. JV declares that she has no competing interests.
Vanderbilt University School of Medicine
Crotched Mountain Foundation
Center for Medical Home Improvement
Adjunct Professor of Pediatrics
Dartmouth Medical School
WCC declares that he has no competing interests.
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