Trisomy 18 (also called Edwards syndrome)
Trisomy 18 is a rare condition that occurs in approximately 1 in 6,000 live births which makes it about ten times rarer that Down syndrome. Ninety-five percent of trisomy 18 is caused by an extra number 18 chromosome and 5% is due to a translocation involving chromosome 18.
Unfortunately, children with trisomy 18 have severe physical birth defects. About 90% of infants with trisomy 18 will have a heart defect and these infants can also have kidney defects, lung and diaphragm abnormalities. Because of their severe physical birth defects about 90% of infants with trisomy 18 will die in the first days of life. Those infants that do survive, have profound mental retardation. Most do not survive beyond the first few months of life, but some children do survive until adolescence.
Trisomy 13 (also called Patau syndrome)
Trisomy 13 (Patau syndrome) is the third most common autosomal abnormality among live births after Down syndrome (trisomy 21) and Edwards syndrome (trisomy 18). Trisomy 13 occurs in about 1 out of every 10,000 newborns. Most trisomy 13 cases result from total trisomy 13 with a very small proportion of trisomy 13 cases due to mosaicism and translocation. Some trisomy 13 fetuses detected in mid-trimester do not survive to term or are stillborn.
Children with trisomy 13 can have cleft lip and palates, extra fingers and toes, malformed and rotated internal organs, severe congenital heart defects and severe brain abnormalities. Because of the severe heart problems, internal organ defects and brain abnormalities, more than 80% of children with trisomy 13 that are liveborn, die in the first month. Less than 5% of infants with trisomy 13 survive into childhood.
47,XXY syndrome (also called Klinefelter syndrome)
Klinefelter syndrome, 47,XXY or XXY syndrome, is a condition caused by a and extra X chromsomes and it occurs in about 1 in 500 males (therefore 1 in 1000 births). Affected individuals have two X chromosomes and one Y chromosome. Many individuals are unaware that they have Klinefelter syndrome as the differences due to having an extra X chromosome are not very obvious and often go undetected.
The main problems seen in Klinefelter syndrome are small testicles and reduced fertility. A variety of other physical and behavioral differences are common, but the severity varies and many boys and men with the condition have few detectable symptoms. People with Klinefelter syndrome is also referred to as "XXY Males", or "47, XXY Males.”
About 1 in 1,000 boys are born with an extra Y chromosome and have a 47,XYY karyotype. Most often, this extra Y chromosome causes no unusual physical features or medical problems. Males with 47,XYY syndrome can sometimes be taller than average and may have an increased risk of learning disabilities and delayed speech and language skills. Developmental delays and behavioral problems are also possible, but these characteristics vary widely among affected boys and men. Most males with 47,XYY syndrome have normal sexual development and are able to conceive children.
47,XXX (also called triplo-X, trisomy X, and XXX syndrome)
About 1 in 1000 girls are born with Triple X syndrome. Triple X syndrome often has no associated physical features or medical problems. A small proportion of women with the condition may have menstrual irregularities and can have learning disabilities, delayed speech, and language skills. Many individuals with 47,XXX syndrome have completely normal physical and mental development.
Trisomy 15 is rare. Most pregnancies with trisomy 15 end in early miscarriage. In pregnancies that have progressed in development, the fetus often has abnormalities of their facial and cranial features, hands, and feet and growth retardation is seen late in pregnancy. Trisomy 15 has been linked to Prader Willi syndrome.
Trisomy 16 is the most common autosomal trisomy seen in miscarriages and accounts for at least 15% of first trimester miscarriages. Most pregnancies with trisomy 16 are lost around 12 weeks although a small percent may be lost in the second trimester. A few fetuses with mosaic trisomy 16 have survived until birth. Most of these infants have growth failure, psychomotor retardation and die in infancy.
Complete trisomy 22 is the second most common finding in miscarriages after trisomy 16. Survival beyond the first trimester of pregnancy is rare. Complete trisomy 22 is very rare. Most affected individuals with complete trisomy 22 die before or shortly after birth due to severe birth defects.
While we tend to focus on trisomy 21 because it is the most common trisomy, it is important to remember that trsiomy is a common occurence in pregnancy. There is no known cause or cure.
Hay, William W., Deterding, Robin R. , Levin, , Myron J., Sondheimer , Judith M., Current Pediatric Diagnosis & Treatment, The McGraw-Hill Companies, Inc. Eighteenth Edition. 2007
Nelson-Anderson, D., Waters, C., Genetic Connection A Guide to Documenting your Individual and Family Health History Sonters Publishing, 1995