what is down syndrome caused by

Down syndrome is caused by an extra copy of chromosome 21 , usually from an error in cell division called nondisjunction. It can also happen from translocation or, more rarely, mosaicism.

What that means

• Typical human cells have 46 chromosomes, arranged in 23 pairs.
• In Down syndrome, there is extra genetic material from chromosome 21.
• That extra material changes how the body and brain develop.

Main types

• Trisomy 21: most common form, with three copies of chromosome 21.

• Translocation Down syndrome: part of chromosome 21 attaches to another chromosome.

• Mosaic Down syndrome: only some cells have the extra chromosome.

Simple takeaway

It is a genetic condition , not something caused by anything a parent did or did not do during pregnancy.