Trisomy 18 or Edward's Syndrome By Austin Scharfstein

How does the disorder occur? Trisomy 18, or Edward's syndrome, is the second most common trisomy after Down's syndrome. Edward's syndrome occurs when three sets (trisomy) of chromosome 18 occur. Trisomy 18 is therefore caused by a genetic abnormality occurring before conception, when egg and sperm cells are made. A healthy egg or sperm cell contains 23 individual chromosomes - one to contribute to each of the 23 pairs of chromosomes needed to form a healthy, 46 chromosome cell. However, sometimes egg and sperm cells are left with 24 (or more) chromosomes. It is the joining of these egg or sperm cells that eventually cause a trisomy fetus to be formed.

A Brief History of the Disorder Trisomy 18 was discovered by John Hilton Edwards, a British geneticist, in His discovery of it led to the association of his name with the syndrome. Edwards (b 1928) served as professor of human genetics at Birmingham University from 1969 to 1979 and at Oxford University from 1979 to He was the author of Human Genetics (1978) as well as numerous papers on a variety of topics in the field.

CanTrisomy 18 Be Passed to Future Generations? Because Trisomy 18 is caused by non- disjunction, it cannot be passed on to future generations. In addition, babies diagnosed with Edwards syndrome rarely live past 5-6 days; fetuses identified with Trisomy 18 are often miscarried or aborted.

Type of Mutation: Trisomy 18 is a gene mutation which is caused by an extra 18th chromosome Where does it occur in a karyotype/chromosome/gene? Where does it occur in a karyotype/chromosome/gene? It occurs in the 18th chromosomal pair

What Are the Phenotypic Effects to the Human Body? Most children born with Edwards' syndrome appear weak and fragile, and they are often underweight. The head is unusually small and the back of the head is prominent. The ears are malformed and low-set, and the mouth and jaw are small (also known as micrognathia). The baby may also have a cleft lip. Often, the hands malformed, clenched into fists with the index finger overlapping the other fingers. The child may have club feet, and toes may be webbed or fused. A number of problems involving the internal organs may be present. Abnormalities often occur in the lungs and diaphragm, and blood vessel malformations are common. Various types of congenital heart disease may be present. The child may have an a hernia, malformed kidneys, and abnormalities of the urogenital system, such as undescended testicles in a male child (cryptochordism).

How Is it Diagnosed? Edwards' syndrome at birth may be diagnosed by the physical abnormalities characteristic to the syndrome. In addition, physical examination of the infant may show arched type fingerprint patterns and xrays may reveal a short breast bone. Definitive diagnosis is achieved through karyotyping, which involves drawing the baby's blood for a microscopic examination of the chromosomes. Using special stains and microscopy, individual chromosomes are identified, and the presence of an extra chromosome 18 is revealed. Edwards' syndrome can be detected before birth. If a pregnant woman is older than 35, has a family history of genetic abnormalities, has previously conceived a child with a genetic abnormality, or has suffered earlier miscarriages, she may undergo tests to determine whether her child carries genetic abnormalities. Potential tests include maternal serum alpha-fetal protein analysis or screening, ultrasonography, amniocentesis, and chorionic villus sampliing. In addition, a pregnant woman carrying a child with Edwards' syndrome may have an unusually large uterus during pregnancy, due to the presence of extra amniotic fluid. An unusually small placenta may be noted during the birth of the child.

How Is it Treated? There is no cure for Edwards syndrome. Ninety to 95 % of all babies born with it die within a year of birth. The few infants that do survive need special treatment--ranging from muscular therapy to nervous system and skeletal corrections--for their various handicaps.

Diagnosis Edwards' syndrome may be diagnosed at birth by the physical abnormalities characteristic to the syndrome. In addition, physical examination of the infant may show arched fingerprint patterns, while xrays may show a short sternum. Definitive diagnosis is achieved through karyotyping, which involves drawing the baby's blood for a micrscopic examination of the chromosomes. Using special stains and microscopy, individual chromosomes are identified, and the presence of an extra chromosome 18 is revealed. Edwards' syndrome can be detected before birth. If a pregnant woman is older than 35, has a family history of genetic abnormalities, has previously conceived a child with a genetic abnormality, or has suffered earlier miscarriages, she may undergo tests to determine whether her child carries genetic abnormalities. Tests include maternal serum alpha- fetal protein analysis or screening, ultrasoundgraphy, amniocentesis, and chorionic villus sampling. serum In addition, a pregnant woman carrying a child with Edwards' syndrome may have an unusually large uterus during pregnancy, due to the presence of extra amniotic fluid. In addition, an unusually small placenta may be noted during birth.

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