Edwards Syndrome, Trisomy 18 8 Sources (

¶ … Edwards Syndrome, Trisomy 18 8 sources ( 4-5 Print Sources 3-4 online Sources) All questions answered essay ( mandatory): -What ? (Discription genetic disorder) -What genes chromosomes linked disorder? -Describe populations affected Edwards Syndrome (Include gender, age & number affected USA wordwide.

Edwards syndrome which is also known as Trisomy 18 is a genetic disorder that is caused by the presence of a third copy of chromosome 18 instead of the normal two copies. The extra 18th chromosome comes as a result of nondisjunction of the chromosomal material during meiosis. As a result of failure in the segregation of a chromosome to the daughter cells, there can be errors in the meiotic division leading to an extra chromosome. This extra chromosome usually occurs before conception and it is the second most common autosomal trisomy that carries to term after Down syndrome though it is more common in females than males and it affects the normal development of a fetus in the womb leading to intrauterine growth retardation leading to children having low birth weight. It leads to effects such as abnormalities of organs or hearth defects. It was named after John H. Edwards who was the first to describe it in the year 1960 Buyse, 1990()

Genes and chromosomes linked to the disorder

Edwards syndrome occurs as a result of a person having a third copy of the genetic material of chromosome 18. It can occur when a person has the whole copy of the 18th chromosome which leads to Trisomy 18 or when they have a part copy of the 18th chromosome which results from translocations. Translocations are extremely rare but when they occur, the person has two copies of the 18th chromosome and the extra material from the 18th chromosome is attached to another different chromosome. The physical signs of partial Edwards syndrome depend largely on the site of attachment of the extra chromosome. If only part of the long arm of chromosome 18 is attached to the other chromosome then the physical signs may be less severe than those typical of trisomy 18. If the entire long arm of the extra chromosome is attached to another chromosome, the physical signs are more severe. There are also a small percentage of cases where only some of the cells of the body have an extra copy of the 18th chromosome which results in a mixed population of cells with their chromosomal numbers differing. This occurs in roughly 5% of the cases and is referred to as mosaic Edwards syndrome. The severity of mosaic Edwards syndrome depends largely on the number and type of cells that have an extra chromosome.

Affected populations

Edwards syndrome occurs in about 1 in every 6,000 live births but it is believed that the incidence is higher as a result of majority of those diagnosed with the condition not surviving the prenatal period as a result of majority of fetuses dying before birth. It is also argued that the risk of conceiving a child with trisomy 18 increases with a woman's age. Roughly 80% of those who are born with the disease are female. Edwards syndrome has a very low survival rate as a result of abnormal development of the heart, kidneys and other internal organs of the person. The median lifespan of children is between 5 and 15 days and less than 8% of infants survive longer than 1 year. Only one percent of children with the disorder get to the age of 10 with the survival rate for mosaic Edwards syndrome being slightly higher Canfield et al., 2006()

Parker, Budd, Draper, and Young (2003)

states that most cases of trisomy 18 are not inherited rather they occur as a result of random nondisjunction during meiosis. Mosaic Edwards syndrome is also not inherited but it is possible to inherit partial trisomy 18. This is because as a result of balanced translocation whereby an unaffected person carries a rearrangement of their genetic material between the 18th chromosome and another chromosome, they can pass this on to their offspring.

Signs and symptoms

Children who are born with trisomy 18 suffer from various conditions as a result of abnormal formation of their kidneys, heart, lungs and other internal organs. These include ventricular or atrial septal defect which are structural defects of the heart, mental retardation as a result of delays in development of the brain or malformation of the brain, arthrogryposis where there are multiple joint contractures at birth, a small head or microcephaly, a small jaw or micrognathia, cleft lip or cleft palate, undescended testicles in males, an unusual shaped chest or pectus carinatum, webbed feet, rocker-bottom feet where the feet have a rounded bottom, crossed legs, clenched hands, low birth weight, absent radius, underdeveloped thumbs or nails, presence of choroid plexus cysts on the brain, short breast bone, ptosis or drooping upper eyelids, palpebral fissures or narrow folds of the eyelids, ocular hypertelorism or widely-spaced eyes, omphalocele or intestines that are protruding out of the body, and low-set ears Rodeck & Whittle, 1999()

Diagnosis

Diagnosis of trisomy 18 is conducted by diagnosing the physical abnormalities that occur as a result of the disorder. During pregnancy, an ultrasononogram exam is conducted which shows the presence of an unusually large uterus, extra amniotic fluid or an unusually small placenta Papp et al., 2007.

Chorionic villus sampling, amniocentesis or alpha-fetal protein analysis can also be conducted to detect the condition. A physical exam of the infant may also be conducted to show unusual patterns of the fingerprints. An x-ray can also be conducted to show a short breast bone. Other signs and symptoms such as cleft lip or palate, undescended testicle, ptosis, low-set ears, omphalocele, micrognathia, and microcephaly can be diagnosed through observation. Karyotyping can also be conducted to identify the specific chromosomes which will show an additional 18th chromosome.