Synonyms: 21q- syndrome | Partial 21q monosomy
Monosomy 21 is a chromosomal anomaly characterized by the loss of variable portions of a segment of the long arm of chromosome 21 that leads to an increased risk of birth defects developmental delay and intellectual deficit.
Data from Orphanet are used to provide information on a disease's name, synonym(s), and overview. Reference: Access aggregated data from Orphanet at Orphadata. Orphadata: Free access data from Orphanet. © INSERM 1999. Available on http://www.orphadata.org. Data version April 2026
Newly diagnosed with
21q deletion syndrome?
Our RARE Concierge Services Guides are available to assist you by providing information, resources and connections as you navigate your rare disease journey.
Advocacy Organizations
Rare Chromosome Disorder Support Group – Unique
Through sharing knowledge and lived experience, Unique helps families and professionals navigate the world of chromosome and gene disorders
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Clinical Trials
For a list of clinical trials in this disease area, please click here.