Monarch Disease Ontology term MONDO_0008608 (Down syndrome) is a chromosomal abnormality caused by the presence of a third (partial or total) copy of the chromosome 21 genetic material and that is characterized by variable intellectual disability, muscular hypotonia, and joint laxity, often associated with a characteristic facial dysmorphism and various anomalies such as cardiac, gastrointestinal, or endocrine defects. Also known as: Down syndrome, Isolated cases, Down's syndrome, Down's syndrome - trisomy 21, Downs syndrome, G trisomy, leukemia, megakaryoblastic, with or without Down syndrome, somatic, trisomy 21 (Down syndrome).