|
Detailed Definition Trisomy 13 is a rare chromosome abnormality, affecting about one in every 5,000 to 10,000 babies, which involves both severe mental retardation and physical birth defects. Most babies with Trisomy 13 do not live longer than a few days, weeks, or months. About 2/3 die before six months of age, and 90% die before their first birthday, although some do live for years. Only |
|
very rarely do children with Trisomy 13 walk or have speech. In addition to mental retardation, babies with Trisomy 13 have physical birth defects. The most common of these are a cleft lip (when the upper lip does not form properly), eyes which are small and closer together than is normal, heart defects, kidney abnormalities, and extra fingers or toes. Sometimes the baby’s brain does not form properly, and instead of having the usual two distinct hemispheres (halves), there is only a single continuous structure. This is called holoprosencephaly. Often the brain abnormality leads to death in the newborn period.
These problems are all caused by an extra chromosome, specifically an extra copy of chromosome number 13. Chromosomes, which normally come in pairs (one in each pair from the mother, and one from the father), are the packages of genetic material which give the baby instructions for growth and development. The extra genetic material that the baby receives interferes with these instructions. The extra chromosome was present in either the sperm or the egg which went to form the baby, and this mistake occurred either prior to or just at conception. Many parents wonder why Trisomy 13 occurred, but we know of nothing that either parent could have done that would have caused or prevented this from happening. It is very unusual for a family to have a second child with Trisomy 13. If you were under 30 years when pregnant with your baby with Trisomy 13, then there is approximately a 1% chance for another baby to have Trisomy 13. If you were over 30, then your risk is not increased; it is simply the same as that of any other woman your age. There is an exception to this statement. Rarely, a baby has Trisomy 13 due not to a complete extra copy of chromosome 13, but rather due to a rearrangement of part of chromosome 13 with another chromosome. These cases are called "translocations" and can run in families, although most of the time they do not. The chromosome study you had during prenatal diagnosis, or when the baby was first diagnosed with Trisomy 13, distinguishes between the more common type of Trisomy 13 and the translocation type. Prenatal diagnosis is an option for you in a future pregnancy, regardless of which type of Trisomy 13 your baby had.
Trisomy 13 can be diagnosed prenatally through CVS or amniocentesis; sometimes an abnormal ultrasound provides the first indication that the baby has a problem. In other cases a baby with Trisomy 13 may be diagnosed shortly after birth. If facial features, a heart defect or other problems raise the possibility of Trisomy 13, a blood chromosome test will be done to confirm the diagnosis.
When a baby is born with Trisomy 18, parents usually need to make some difficult decisions about whether to use medical interventions to prolong the baby's life, or whether to simply give the baby supportive care to make him or her as comfortable as possible. You can receive help and support in this process from the baby's doctor, the nursery social worker, hospital chaplain and your genetic counselor.
If you have learned during your pregnancy
that your baby has Trisomy 13 and are trying to decide whether
or not to continue your pregnancy, you will probably not find
many sources of information on this condition. There is an
organization called SOFT (Support |
