Chromosomal abnormalities that cause birth defects including Down syndrome.

Chromosomes in the human body generally come in pairs. Most people have 23 pairs of chromosomes, for a total of 46. When an extra chromosome is present in one of the pairs (resulting in three instead of two), the abnormality is labeled trisomy. Scientists have numbered the 23 pairs of human chromosome, and the trisomy abnormality may occur in several different chromosomes. For example, when the trisomy abnormality occurs in chromosome 21, the result is Down syndrome. Babies born with Down syndrome usually survive into adulthood.

Other chromosomal abnormalities are trisomy 13, Patau's syndrome, and trisomy 18, Edward's syndrome. Both are relatively rare but serious conditions that cause severe mental retardation and physical deformities. Babies born with either of these trisomies usually do not survive beyond their first year.

For Further Study

Organizations

Support Organization for Trisomyl3/18 (SOFT)
Address: 5030 Cole
Pocatello, ID 93202
(Organization for families of children with trisomy 13 or 18. Publishes a newsletter, SOFT Touch, and a book, Trisomy 18: Book for Families.)