Down syndrome or trisomy 21 is a trisomic condition in which the zygote inherits an extra chromosome 21 for a total of 47 chromosomes, due to non-disjunction of chromosomes. It happens in about 1 in 800 births, a big proportion comparing with other syndromes. Down syndrome can be predicted through amniocentesis, but not prevented. The possibility to be born a baby with down syndrome is increased when the mother is older. In Down syndrome there are mental and physical disfunctions like heart disease, celiac disease, eye problems, hearing, skeletal intestinal problems, dementia and thyroid disfunctions. A Down person has some characteristics like flat face, short neck, abnormally shaped ears, poor muscle tone, small hands and feet    .
- ↑ http://kidshealth.org/parent/medical/genetic/down_syndrome.html#
- ↑ http://www.nichd.nih.gov/health/topics/down_syndrome.cfm
- ↑ http://www.nlm.nih.gov/medlineplus/downsyndrome.html
- ↑ http://www.medicinenet.com/down_syndrome/article.htm