Trisomy 18 or Trisomy 18 or Edward's SyndromeEdward's Syndrome

By Austin ScharfsteinBy Austin Scharfstein

How does the disorder occur?How does the disorder occur? Trisomy 18, or Edward's syndrome, is the second Trisomy 18, or Edward's syndrome, is the second

most common trisomy after Down's most common trisomy after Down's syndrome. Edward's syndrome occurs when syndrome. Edward's syndrome occurs when three sets (trisomy) of chromosome 18 occur. three sets (trisomy) of chromosome 18 occur.

Trisomy 18 is therefore caused by a genetic Trisomy 18 is therefore caused by a genetic abnormality occurring before conception, abnormality occurring before conception, when egg and sperm cells are made. A when egg and sperm cells are made. A healthy egg or sperm cell contains 23 healthy egg or sperm cell contains 23 individual chromosomes - one to contribute to individual chromosomes - one to contribute to each of the 23 pairs of chromosomes needed each of the 23 pairs of chromosomes needed to form a healthy, 46 chromosome cell. to form a healthy, 46 chromosome cell. However, sometimes egg and sperm cells However, sometimes egg and sperm cells are left with 24 (or more) chromosomes. It is are left with 24 (or more) chromosomes. It is the joining of these egg or sperm cells that the joining of these egg or sperm cells that eventually cause a trisomy fetus to be eventually cause a trisomy fetus to be

formedformed..

A Brief History of the DisorderA Brief History of the Disorder

Trisomy 18 was discovered by John Hilton Trisomy 18 was discovered by John Hilton Edwards, a British geneticist, in 1960. His Edwards, a British geneticist, in 1960. His discovery of it led to the association of his name discovery of it led to the association of his name with the syndrome.with the syndrome.

Edwards (b 1928) served as professor of human Edwards (b 1928) served as professor of human genetics at Birmingham University from 1969 to genetics at Birmingham University from 1969 to 1979 and at Oxford University from 1979 to 1979 and at Oxford University from 1979 to 1995. He was the author of 1995. He was the author of Human GeneticsHuman Genetics (1978) as well as numerous papers on a variety (1978) as well as numerous papers on a variety of topics in the field. of topics in the field.

CanTrisomy 18 Be Passed to CanTrisomy 18 Be Passed to Future Generations?Future Generations?

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

Type of Mutation:Type of Mutation:

Trisomy 18 is a gene mutation which is Trisomy 18 is a gene mutation which is caused by an extra 18th chromosome caused by an extra 18th chromosome

Where does it occur in a Where does it occur in a karyotype/chromosome/gene?karyotype/chromosome/gene?

It occurs in the 18th chromosomal pair It occurs in the 18th chromosomal pair

What Are the Phenotypic Effects to What Are the Phenotypic Effects to the Human Body?the Human Body?

Most children born with Edwards' syndrome Most children born with Edwards' syndrome appear weak and fragile, and they are often appear weak and fragile, and they are often underweight. The head is unusually small underweight. The head is unusually small and the back of the head is prominent. The and the back of the head is prominent. The ears are malformed and low-set, and the ears are malformed and low-set, and the mouth and jaw are small (also known as mouth and jaw are small (also known as micrognathia). The baby may also have a micrognathia). The baby may also have a cleft lip. Often, the hands malformed, cleft lip. Often, the hands malformed, clenched into fists with the index finger clenched into fists with the index finger overlapping the other fingers. The child may overlapping the other fingers. The child may have club feet, and toes may be webbed or have club feet, and toes may be webbed or fused.fused.

A number of problems involving the internal A number of problems involving the internal organs may be present. Abnormalities often organs may be present. Abnormalities often occur in the lungs and diaphragm, and blood occur in the lungs and diaphragm, and blood vessel malformations are common. Various vessel malformations are common. Various types of congenital heart disease may be types of congenital heart disease may be present. The child may have an a hernia, present. The child may have an a hernia, malformed kidneys, and abnormalities of the malformed kidneys, and abnormalities of the urogenital system, such as undescended urogenital system, such as undescended testicles in a male child (cryptochordism).testicles in a male child (cryptochordism).

How Is it Diagnosed?How Is it Diagnosed?Edwards' syndrome at birth may be diagnosed by the physical abnormalities Edwards' syndrome at birth may be diagnosed by the physical abnormalities characteristic to the syndrome. In addition, physical examination of the infant may 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. show arched type fingerprint patterns and xrays may reveal a short breast bone. Definitive diagnosis is achieved through karyotyping, which involves drawing the Definitive diagnosis is achieved through karyotyping, which involves drawing the baby's blood for a microscopic examination of the chromosomes. Using special stains 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 and microscopy, individual chromosomes are identified, and the presence of an extra chromosome 18 is revealed.chromosome 18 is revealed.

Edwards' syndrome can be detected before birth. If a pregnant woman is older than 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 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 with a genetic abnormality, or has suffered earlier miscarriages, she may undergo tests to determine whether her child carries genetic abnormalities. Potential tests tests to determine whether her child carries genetic abnormalities. Potential tests include maternal serum alpha-fetal protein analysis or screening, ultrasonography, include maternal serum alpha-fetal protein analysis or screening, ultrasonography, amniocentesis, and chorionic villus sampliing.amniocentesis, and chorionic villus sampliing.

In addition, a pregnant woman carrying a child with Edwards' syndrome may have an 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. 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.An unusually small placenta may be noted during the birth of the child.

How Is it Treated?How Is it Treated?

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

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

BibliographyBibliography

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