only human autosomal trisomy where people last longer than a year past birth
-1/800 live births
-250,000 individuals currently in United States with Down syndrome
-Down syndrome has 12 to 14 characteristics, and affected individuals express 6 to 8 on average (Figure 6-2).
Prominent epicanthic fold in each eye
Flat face, round head, short stature with protruding tongue
Short, broad hands with characteristic palm and fingerprint pattern
Mental retardation, average life span 50 years.
-Children are prone to respiratory disease and heart malformations.
Show a higher incidence of leukemia (20 times higher)
Death in older individuals often due to Alzheimer's disease, which usually occurs earlier than in normal population.
-People with syndrome have decreased risk in some cancers because of an extra copy of the DSCR1 which seems to be associated with decreased risk of some cancers.
Approximately 10% reduction
-as the age of childbearing women exceeds 45, the probability of Down syndrome births continues to increase substantially.
Down syndrome is caused by a random error—nondisjunction of chromosome 21, thus the disorder is not expected to be inherited.
Nevertheless, Down syndrome occasionally runs in families (familial Down syndrome).
Translocation of bottom part of chromosome 21 onto another chromosome