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Our Trisomy 18 Angel Q & A about Trisomy 18

What is Trisomy 18?
	Trisomy 18 also known as "Edwards syndrome" is named after the physician who first described the disorder. Trisomy 18 is a genetic disorders that is seen in about one in every 3,000 live births, that present a combination of birth defects including severe mental retardation, as well as health problems involving nearly every organ system in the body. Twenty to 30 percent of babies born with trisomy 18 die in the first month of life, and 90 percent die by age 1. It is important to note that 5 to 10 percent of babies with trisomy 18 do survive the first year of life. Therefore, these disorders are not universally fatal and, in the absence of any immediate life-threatening problems, accurate predictions of life expectancy are difficult to make. There are those 5 to 10 percent with trisomy 18 that survive to their early childhood and teens, however, it is very rare.
What causes Trisomy 18?
	Usually each egg and sperm cell contains 23 chromosomes. The union of these creates 23 pairs, or 46 total chromosomes at the time of fertilization. In this manner, a person receives exactly half of their genetic material from each parent. Sometimes, an error occurs when an egg or sperm cell is forming, causing it to have an extra chromosome #18. When this cell contributes the extra chromosome 18 to the embryo, trisomy 18 results. The extra chromosome 18 can come from either the mother's egg cell or the father's sperm cell. The features of trisomy 18 result from having this extra chromosome 18 in each of the body's cells. Occasionally, the extra chromosome 18 is attached to another chromosome in the egg or sperm; this is called a translocation. This is the only form of trisomy 18 that can be inherited in a family. Sometimes, a parent can carry a "balanced" rearrangement where chromosome 18 is attached to another chromosome. However, since the parent does not have any extra or missing chromosome material, they are said to have a "balanced translocation" and they are usually normal and healthy. Rarely, mosaic trisomy 18 may occur when the error in cell division occurs after fertilization. These persons have some cells with an extra chromosome 18 and others with the normal number.
What type of medical problems could my baby have?
	Babies with trisomy 18 appear thin and frail. They fail to thrive and have problems feeding. Trisomy 18 causes a small head size, with the back of the head (strawberry shaped) prominent. Ears are usually low set on the head. The mouth and jaw are unusually small, and there is a shortened sternum (breastbone). At birth, these babies are small for their age, even when delivered full-term, and have a weak cry. Their response to sound can be decreased and there is often a history of infrequent fetal activity during the pregnancy. About 90 percent of babies with trisomy 18 have heart defects. They clench their fists in a characteristic manner and extending the fingers fully is difficult. Joint contractures - where the arms and legs are in a bent position, rather than relaxed - are usually present. The feet may be referred to as "rocker bottom" due to their shape, and also club feet. Babies with trisomy 18 may also have spina bifida, eye problems, cleft lip and palate, and hearing loss. It is also common to see feeding problems, slow growth, seizures, high blood pressure, kidney problems and scoliosis. In males, the testes fail to descend into the scrotum. Most babies with trisomy 18 have problems which affect all parts of the body in some way. Most children with trisomy 18 will have some, but not all, of the health problems mentioned above.
Could this happen to another child of ours?
	In general, the chance of having another baby with trisomy 18 is no greater than 1 percent. The risk to have a baby with trisomy 18 increases slightly with each added year of maternal age. After birth, the physician usually can takes a blood sample from your baby and perform a chromosomal analysis (called a karyotype). This confirms the physical findings of trisomy 18 and determines the underlying chromosomal abnormality. This information is important in determining the risk in future pregnancies. (Translocation and mosaic trisomy 18 have different recurrence risks). The physician may refer parents to a genetic physician or genetic counselor who can explain the results of chromosomal tests in detail.

Q & A about Trisomy 18