Edwards syndrome
Synonyms and Key Words: Edwards syndrome, Edwards' syndrome, trisomy 18 syndrome, trisomy E syndrome, severe psychomotor retardation, severe growth retardation, microcephaly, microphthalmia, malformed ears, micrognathia, retrognathia, microstomia, clenched fingers, congenital malformations, cardiac malformations, renal malformations, polyhydramnios, oligohydramnios, small placenta, single umbilical artery, intrauterine growth retardation, weak fetal activity, fetal distress, delayed psychomotor development, mental retardation, neonatal hypotonia, cerebellar hypoplasia, meningoencephalocele, anencephaly, hydrocephaly, holoprosencephaly, Arnold-Chiari malformation, hypoplasia of corpus callosum, aplasia of corpus callosum, defective falx cerebri, frontal lobe defect, migration defect, arachnoid cyst, myelomeningocele, ocular hypertelorism, epicanthal folds, short palpebral fissures, iris coloboma, cataract, corneal clouding, abnormal retinal pigmentation, short nose with upturned nares, choanal atresia, narrow palatal arch, cleft lip, cleft palate, preauricular tags, camptodactyly, limited hip abduction, narrow pelvis, short sternum, short neck with excessive skin folds, dorsiflexed great toes, hypoplastic nails, radial aplasia, radial hypoplasia, thumb aplasia, syndactyly of the second and third digits, arthrogryposis, rocker-bottom feet with prominent calcanei, talipes equinovarus, ventricular septal defects, poly-valvular heart disease, pulmonary valve defects, aortic valve defects, atrial septal defects, patent ductus arteriosus, overriding aorta, coarctation of aorta, hypoplastic left heart syndrome, tetralogy of Fallot, transposition of great arteries, pulmonary hypoplasia, abnormal lobation of lung, omphalocele, malrotation of the intestine, ileal atresia, common mesentery, Meckel diverticulum, esophageal atresia, tracheoesophageal fistula, diaphragmatic eventration, prune belly anomaly, diastasis recti, absent gallbladder, absent appendix, accessory spleens, exstrophy of Cloaca, pyloric stenosis, imperforate anus, malpositioned anus, pilonidal sinus, hernias, micro multicystic kidneys, double ureters, megaloureters, hydroureters, hydronephrosis, horseshoe kidneys, unilateral renal agenesis, cryptorchidism, hypospadias, micropenis, hypoplasia of labia, hypoplasia of ovaries, hypoplastic ovaries, clitoral hypertrophy, bifid uterus, thymic hypoplasia, thyroid hypoplasia, adrenal hypoplasia, clinodactyly of the fifth fingers, single flexion crease, transverse palmar crease, increased atd angle, postzygotic mitotic errors

# Overview
Trisomy 18 or Edwards Syndrome (named after John H. Edwards, who first described the syndrome in 1960) is a genetic disorder. It is the most common trisomy after Down Syndrome.

# Etiology
It is caused by the presence of three  instead of two  chromosomes 18 in a fetus or baby's cells.
The additional chromosome usually occurs before conception. 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 normal cell with 46 chromosomes. Numerical errors arise at either of the two meiotic divisions and cause the failure of segregation of a chromosome into the daughter cells (non-disjunction). This results in an extra chromosome making the haploid number 24 rather than 23. Fertilization of these eggs or sperm that contain an extra chromosome results in trisomy, or three copies of a chromosome rather than two.

# Incidence/prevalence
The rate of occurrence for Edwards Syndrome is ~ 1:3000 conceptions and 1:6000 live births, as 50% of those diagnosed prenatally with the condition will not survive the prenatal period. Although women in their 20s and 30s may conceive Edwards Syndrome babies, there is an increased risk of conceiving a child with Edwards Syndrome as a woman's age increases.

# Variations
A small percentage of cases occur when only some of the body's cells have an extra copy of chromosome 18, resulting in a mixed population of cells with a differing number of chromosomes. Such cases are sometimes called mosaic Edwards syndrome. Very rarely, a piece of chromosome 18 becomes attached to another chromosome (translocated) before or after conception. Affected people have two copies of chromosome 18, plus extra material from chromosome 18 attached to another chromosome. With a translocation, the person has a partial trisomy for chromosome 18 and the abnormalities are often less than for the typical Edwards syndrome.

# Features and characteristics
Symptoms and findings may be extremely variable from case to case. However, in many affected infants, the following may be found:
- Arthrogryposis a muscle disorder that causes multiple joint contractures at birth
- Growth deficiency
- Feeding difficulties
- Breathing difficulties
- Developmental delays
- Mental retardation
- Undescended testicles in males
- Prominent back portion of the head
- Small head (microcephaly)
- Low-set, malformed ears
- Abnormally small jaw (micrognathia)
- Small mouth
- Cleft lip/Cleft palate
- Upturned nose
- Narrow eyelid folds (palpebral fissures)
- Widely-spaced eyes (ocular hypertelorism)
- Drooping of the upper eyelids (ptosis)
- Overlapped, flexed fingers
- Underdeveloped or absent thumbs
- Underdeveloped nails
- Absent radius
- Webbing of the second and third toes
- Clubfeet or Rocker bottom feet
- Small  pelvis with limited movements of the hips
- Short breastbone
- Kidney malformations
- Structural heart defects at birth (i.e., ventricular septal defect, atrial septal defect, patent ductus arteriosus)

# Presentation
The extra genetic information from the third chromosome causes the abnormalities characteristic of individuals with Edwards Syndrome.   Since every cell in the body contains extra information, the ability to grow and develop appropriately is delayed or impaired.  This results in characteristic physical abnormalities such as low birth weight; a small, abnormally shaped head; small jaw; small mouth; low-set ears; and clenched fists with overlapping fingers. A characteristic "rocker bottom" foot is also common. Babies with Edwards syndrome also have heart defects, and other organ malformations such that most systems of the body are affected.

# Prognosis
The survival rate for Edwards Syndrome is very low. About half die in utero. Of liveborn infants, only 50% live to 2 months, and only 5 - 10% will survive their first year of life. Major causes of death include apnea and heart abnormalities. It is impossible to predict the exact prognosis of an Edwards Syndrome child during pregnancy or the neonatal period. As major medical interventions are routinely withheld from these children, it is also difficult to determine what the survival rate or prognosis would be for the condition if they were treated with the same aggressiveness as their genetically normal peers.