Understanding Down syndrome starts with the facts. Down syndrome is a genetic condition caused by an extra copy of chromosome 21 — which is why it is also called trisomy 21. It is one of the most common chromosomal conditions, and children with Down syndrome live full, active lives.
What causes Down syndrome?
Typically, each cell has 46 chromosomes. In Down syndrome there is an extra full or partial copy of chromosome 21, making 47. This extra genetic material changes how the body and brain develop. It is not caused by anything a parent did or did not do.
The three types
- Trisomy 21 — the most common, where every cell has an extra chromosome 21.
- Translocation — extra chromosome 21 material attaches to another chromosome.
- Mosaic — only some cells carry the extra chromosome.
Facts that reassure
Children with Down syndrome reach the same milestones as other children, usually on a longer timeline. With early support, health care and inclusive education, they thrive. Ongoing research — including infant brain imaging studies — continues to improve how early that support can begin.
Where to go next
If your child has recently been diagnosed, start with the early signs in infants and early intervention therapies, then reach out to your care team.