Down syndrome true true Downs syndrome disease_ontology MTHICD9_2006:758.0 ORDO:870 Down's syndrome - trisomy 21 MESH:D004314 NCI:C2993 DOID:14250 OMIM:190685 ICD10CM:Q90.9 trisomy 21 syndrome G Trisomy NCI2004_11_17:C2993 Complete trisomy 21 syndrome GARD:10247 UMLS_CUI:C0013080 A chromosomal disease that is characterized by flat-looking facial features and weak muscle tone (hypotonia) in infancy and is caused by trisomy of all or a critical portion of chromosome 21 and is associated with intellectual disability. CSP2005:1254-8068 OMIM mapping confirmed by DO. [SN]. Down syndrome is a common chromosomal disorder with well-recognized dysmorphic features, epilepsy occurs in approximately 10% of individuals and age of seizure onset is bimodal with 40% having seizures before 1 year of age (commonly epileptic spasms) and 40% having seizures from the third decade of life. All major seizure types have been described in children with Down syndrome including focal seizures, epileptic spasms, myoclonic and generalized tonic-clonic seizures. Phenotypes seen may also include reflex (startle-induced) seizures. Co-existing acquired structural brain abnormalities may occur, as a consequence of congenital cardiac disease. Down's syndrome ICD10CM:Q90 ICD9CM:758.0 SNOMEDCT_US_2018_03_01:41040004 chromosomal anomaly