Edwards Syndrome (Trisomy 18)

Definition

Definition of Edwards Syndrome (Trisomy 18)
Edwards syndrome (known as Trisomy 18 (T18) or Trisomy E) is a genetic disorder caused by the presence of all or part of an extra 18th chromosome. It is named after John H. Edwards, who first described the syndrome in 1960. It is the second most common autosomal trisomy, after Down syndrome, that carries to term.

Symptoms

Symptoms of Edwards Syndrome (Trisomy 18)
Children born with Edwards syndrome may have some or all of the following characteristics: kidney malformations, structural heart defects at birth (i.e., ventricular septal defect, atrial septal defect, patent ductus arteriosus), intestines protruding outside the body (omphalocele), esophageal atresia, mental retardation, developmental delays, growth deficiency, feeding difficulties, breathing difficulties, and arthrogryposis (a muscle disorder that causes multiple joint contractures at birth).

Some physical malformations associated with Edwards syndrome include small head (microcephaly) accompanied by a prominent back portion of the head (occiput); low-set, malformed ears; abnormally small jaw (micrognathia); cleft lip/cleft palate; upturned nose; narrow eyelid folds (palpebral fissures); widely spaced eyes (ocular hypertelorism); drooping of the upper eyelids (ptosis); a short breast bone; clenched hands; choroid plexus cysts; underdeveloped thumbs and or nails, absent radius, webbing of the second and third toes; clubfoot or Rocker bottom feet; and in males, undescended testicles.

Causes

Causes of Edwards Syndrome (Trisomy 18)
Edwards syndrome is caused by the presence of three – as opposed to two – copies of chromosome 18 in a fetus's or infant's cells. Edwards' syndrome occurs in around one in 6,000 live births and around 80 per cent of those affected are female. The majority of fetuses with the syndrome die before birth. The incidence increases as the mother's age increases. The syndrome has a very low rate of survival, resulting from heart abnormalities, kidney malformations, and other internal organ disorders.

Diagnosis

Diagnosis of Edwards Syndrome (Trisomy 18)
A diagnosis of Edward's syndrome may be reached by the physical abnormalities that are characteristic to the syndrome. A physical examination of the infant can show arched-type finger print patterns, for example, while X-rays can show a shortened breast bone. A more definitive diagnosis can be reached through, 'karyotyping,' which involves taking a sample of the infant's blood for examination of their chromosomes. Through use of specific stains and microscopy, identification of specific chromosomes is possible and the presences of an additional chromosome eighteen is shown.

Edward's syndrome is something that may be detected prior to the birth of the child. Potential testing includes maternal serum alpha-fetal protein analysis or screening, amniocentesis, ultrasonography, and chorionic villus sampling. A woman who is pregnant with a child who has Edward's syndrome might have an uncommonly large uterus during the pregnancy because of the presence of extra amniotic fluid. An unusually small placenta might be noted during the birth of the child.

Genetics

Genetics of Edwards Syndrome (Trisomy 18)
Edwards syndrome is a chromosomal abnormality characterized by the presence of an extra copy of genetic material on the 18th chromosome, either in whole (trisomy 18) or in part (such as due to translocations). The additional chromosome usually occurs before conception. The effects of the extra copy vary greatly, depending on the extent of the extra copy, genetic history, and chance. Edwards syndrome occurs in all human populations but is more prevalent in female offspring.

A healthy egg or sperm cell contains individual chromosomes, each of which contributes to the 23 pairs of chromosomes needed to form a normal cell with a typical human karyotype of 46 chromosomes. Numerical errors can arise at either of the two meiotic divisions and cause the failure of a chromosome to segregate into the daughter cells (nondisjunction). This results in an extra chromosome, making the haploid number 24 rather than 23. Fertilization of eggs or insemination by sperm that contain an extra chromosome results in trisomy, or three copies of a chromosome rather than two.

Treatment

Treatment of Edwards Syndrome (Trisomy 18)
Medical science has not found a cure for Edward's syndrome at this time. Babies with the syndrome commonly present with major physical abnormalities and doctors face hard choices in regards to their treatment. Surgery can treat some of the issues related to the syndrome, yet extreme and invasive procedures might not be in the best interests of an infant whose lifespan could be measured in weeks or even days. Treatment today consists of palliative care.

Approximately five to ten-percent of children with Edward's syndrome survive beyond their first year of life, requiring treatments that are appropriate for the various and chronic effects that are associated with the syndrome. Problems related to nervous system abnormalities and muscle tone affect the development of the infant's motor skills, potentially resulting in scoliosis and crossed eyes or, 'esotropia.' Forms of surgical intervention might be limited due to the child's cardiac health.

Infants with Edward's syndrome can experience constipation caused by poor abdominal muscle tone, something that can be a life-long problem. The results can be discomfort, fretfulness, and feeding issues. Special milk formulas, anti-gas medications, laxatives, stool softeners, as well as suppositories are potential treatments a doctor may recommend. Enemas are something that should not be given to a child with Edward's syndrome because they can deplete the child's electrolytes and alter their body fluid composition.

Prognosis

Prognosis of Edwards Syndrome (Trisomy 18)
In England and Wales, there were 495 diagnoses of Edwards syndrome (trisomy 18) in 2008/2009, of which 92% were made prenatally. There were 339 medical terminations, 49 stillbirths/miscarriages/fetal deaths, 72 unknown outcomes, and 35 live births. Because approximately 3% of cases of Edwards' syndrome with unknown outcomes are likely to result in a live birth, the total number of live births is estimated to be 37 (2008/09 data are provisional). Major causes of death include apnea and heart abnormalities. It is impossible to predict the exact prognosis of a child with Edwards syndrome during pregnancy or the neonatal period. Half of infants with this condition do not survive beyond the first week of life. The median lifespan is 5–15 days. About 8% of infants born with this syndrome survive longer than 1 year, 1% of children live to age 10, typically in less severe cases of the mosaic Edwards syndrome. The small percentage of babies with the full Edwards syndrome who survive birth and early infancy may live to adulthood, and children with mosaic or partial forms of this trisomy may have a completely different and much more hopeful prognosis.