Causes
23 pairs of chromosomes inherited from parents are normally contained in every cell of the human body. When a sperm and an egg unite to form an embryo, their chromosomes unite. The child receives 23 chromosomes from the father's sperm and 23 from the mother's egg - 46 in total.
Sometimes an egg or sperm cell has the wrong number of chromosomes. Since the cells of the father and mother are connected, this distortion is transmitted to the child.
Trisomy means that the baby has an extra chromosome in all or some of its cells. With trisomy 18, the baby has three chromosomes 18. This leads to abnormal development of many organs in the baby.
Typically, trisomy 18 is caused by an extra chromosome 18 in every cell. About 5% of affected people have an extra chromosome 18 in some cells, not all. This is a mosaic trisomy. It can be very heavy or barely noticeable, depending on the number of cells that have an extra chromosome.
In rare cases, there is no extra chromosome; part of the long branch of chromosome 18 connects to another chromosome during sperm and egg production or early embryo development. In this case, the individual has 2 chromosomes 18 and additional material from chromosome 18, which is attached to another chromosome. This phenomenon is called translocation.
The extra genetic material causes developmental abnormalities in the same way as having the entire extra chromosome. The signs and symptoms of this form of trisomy depend on the amount of chromosomal material that has been transferred to the other chromosome.
About inheritance mechanism
Most cases of the syndrome are not inherited. It occurs due to random events during the production of the egg and sperm. As a result of an error in division, a reproductive cell with the wrong number of chromosomes appears. For example, a sperm or egg may have an extra copy of chromosome 18. When one of these atypical reproductive cells contributes to a child's genetic makeup, the child will have an extra chromosome 18 in all of its cells.
Mosaic trisomy 18 is also not inherited. It is caused by random events during cell division at the beginning of embryonic development. As a result, individual cells contain two copies of chromosome 18, while others contain three copies of this chromosome.
Translocation trisomy may be inherited. An unaffected person carries a rearrangement of genetic material between chromosome 18 and another chromosome. Although he has no signs of trisomy 18, a person who has this type of translocation is at an increased risk of having children with this genetic disorder.
Epidemiology
Edwards syndrome is the second most common autosomal trisomy among living children after Down's syndrome.
Trisomy 18 occurs on average in 1 in every 5,000 children. Any woman can have a baby with trisomy 18, but the risk increases with the age of the mother.
Signs of Edwards syndrome
Babies born with trisomy 18 may have some or all of these characteristics:
- malformations of the kidneys;
- structural defects of the heart at birth (defect of the interventricular and atrial septa, patent ductus arteriosus);
- intestines protruding outside the body (omphalocele);
- esophageal atresia (obstruction of the esophagus);
- mental retardation;
- developmental delay;
- growth deficit;
- difficulty feeding;
- difficulty breathing;
- arthrogryposis (joint stiffness).
Some of the physical malformations associated with Edwards syndrome include:
- small head (microcephaly);
- low-set, malformed ears;
- abnormally small jaw (micrognathia);
- cleft lip / cleft palate;
- inverted nose;
- narrow, wide-set eyes (ocular hypertelorism);
- drooping of the upper eyelids (ptosis);
- short sternum;
- clenched hands;
- underdeveloped thumbs and / or nails;
- fusion of the second and third toes;
- clubfoot;
- boys have undescended testicles.
In utero, the most common characteristic is cardiac and CNS abnormalities. The most common intracranial pathology is the presence of choroid plexus cysts, which are pockets of fluid in the brain. Excess amniotic fluid sometimes appears.
Diagnostics
In newborns, chromosome analysis can be done to determine the exact cause of birth defects.
Possible prenatal studies for trisomy 18:
- Measurement of alpha-fetoprotein levels. The test is performed between 15 and 17 weeks of gestation. A positive test result does not mean that the child will have trisomy 18 or any chromosomal abnormality. In fact, only about 11% of those women who test positive for trisomy 18 on this test will actually have an affected fetus.
- Ultrasound is another widely used screening test. As with the above study, a simple ultrasound scan cannot be used to diagnose trisomy 18. A more detailed study using ultrasound waves can be performed to look for characteristic signs of anomaly, but this method cannot confirm the presence of the syndrome.
- Analysis of embryonic chromosomal material obtained from amniocentesis or chorionic villus sampling is necessary to prove that there is an additional copy of chromosome 18. Amniocentesis is usually performed at 15-18 weeks of gestation and is the most commonly used test for prenatal diagnosis of trisomy 18. During this procedure A thin needle is inserted through the abdominal wall and a small sample of amniotic fluid is taken. Chorionic villus sampling is another type of study that allows you to study the genetic material of the fetus. The test is performed 10 to 12 weeks after the last menstrual cycle and therefore has the advantage of allowing an earlier diagnosis. This procedure involves collecting a sample of chorionic villi from the placenta by puncturing the abdominal wall or using a catheter through the vagina.
Treatment
Currently, medical science has not found a cure for Edward's syndrome. Infants with the syndrome usually have severe physical impairments and doctors have difficulty making choices about their treatment. Surgery can help treat some of the problems associated with the syndrome. Today, treatment mainly consists of palliative care (maintaining and improving the quality of life of affected patients).
Approximately 5-10% of children with Edward's syndrome survive after the first year of life thanks to the treatment of various chronic pathologies associated with the syndrome. Problems associated with nervous system abnormalities and muscle tone affect the development of motor skills in the infant, which can lead to scoliosis and strabismus. The use of surgical techniques is limited due to the heart disease present.
Babies with Edward's syndrome may have constipation due to poor abdominal muscle tone. This can result in discomfort, irritability, and eating problems. Specialty formula milk, gas medications, laxatives, stool softeners, and suppositories are potential treatments that a doctor may recommend.
Enemas are not recommended as they can drain electrolytes and alter body fluids.
Affected children have severe developmental delays, although with early intervention through therapy and special education programs, they can reach certain developmental milestones. These patients are at increased risk of developing Wilms' tumor, a form of kidney cancer that predominantly affects children. It is recommended to regularly perform ultrasound of the abdominal organs.
Conclusion
The average life expectancy for half of the children born with this syndrome is less than two months; about 90 to 95% of these children die before their first birthday. 5-10% of patients who survived their first year have severe developmental disabilities.
Children who are one year old need support while walking and their ability to learn is limited. Verbal communication skills are also limited, although they are able to respond to comfort, and can learn to smile, recognize parents and other people, and interact with them.
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