Genetics

Down syndrome is caused by an extra (third) chromosome 21. Individuals with Down syndrome have therefore not 46, but 47 chromosomes. Whereas everyone has two chromosomes 21, they have 3. Therefore, Down syndrome is also called trisomy 21. The trisomy is usually due to an abnormality of the egg of the mother: normally all reproductive […]

As a woman is born with all her egg cells, the risk of a chromosome anomaly in the egg cell increases with her age.

When a pregnant woman is 30 yrs, the risk on Down syndrome is 1 on 1000 (0.1 %); at the age of 40 yrs the risk is 1 on 100 (1 %), […]