Edwards' Syndrome Health Article

Definition

Edwards' syndrome is caused by an extra (third) copy of chromosome 18. The extra chromosome is lethal for most babies born with this condition. It causes major physical abnormalities and severe mental retardation. Very few children afflicted with this syndrome survive beyond the first year.

Description

Edwards' syndrome is associated with the presence of a third copy of chromosome number 18. Humans normally have 23 pairs of chromosomes. Chromosomes are numbered 1–22, and the 23rd pair is composed of the sex chromosomes, X and Y. A person inherits one set of 23 chromosomes from each parent. Occasionally, a genetic error occurs during egg or sperm cell formation. A child conceived with such an egg or sperm cell may inherit an incorrect number of chromosomes. In the case of Edwards' syndrome, the child inherits three (trisomy), rather than two, copies of chromosome 18. Ninety-five percent of the children are full trisomies, 2 percent are due to translocations, where only part of an extra chromosome is present (this may be hereditary), while 3 percent are mosaic trisomies, where the extra chromosome is present in some but not all of the cells.

Edwards' syndrome is usually fatal, with most babies dying before birth. Of those who do make it to birth, 20–30 percent die within one month. However, a small number of babies (less than 10 percent) live at least one year.

Edwards' syndrome is also referred to as trisomy 18, trisomy E, and trisomy 16–18. It is the second most common trisomy, after trisomy 21 (Down syndrome).

Demographics

Edwards' syndrome occurs in approximately one in every 5,000 live births and one in every 5,000 stillborn births; it affects girls more often than boys. Women older than their early thirties have a greater risk of conceiving a child with Edwards' syndrome, but it can also occur with younger mothers.

Causes and symptoms

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

Numerous problems involving the internal organs may be present. Abnormalities often occur in the lungs and diaphragm (the muscle that controls breathing), and blood vessel malformations are common. Various types of congenital heart disease, including ventricular septal defect (VSD), atrial septic defect (ASD), or PDA (patent ductus arteriosus), may be present. The child may have an umbilical or inguinal hernia, malformed kidneys, and abnormalities of the urogenital system, including undescended testicles in a male child (cryptochordism).

When to call the doctor

A child with Edwards' syndrome is likely to have many medical and development needs. Parents should develop good working relationships with their doctor, other specialists, and therapists, and should consult them as needed.

If a woman gives birth to a child with Edwards' syndrome and plans to have another child, a doctor as well as a genetic counselor should be consulted so that prenatal screening and genetic counseling can be conducted.

Diagnosis

Edwards' syndrome at birth may be diagnosed by the physical abnormalities characteristic to the syndrome. Physical examination of the infant may show arched type finger print patterns, while x rays may reveal a short breast bone (sternum). Definitive diagnosis is achieved through karyotyping, which involves drawing the 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 chromosome 18 is revealed.

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 with a genetic abnormality, or has suffered earlier miscarriages, she may undergo tests to determine whether her child carries genetic abnormalities. Potential tests include maternal serum alpha-fetal protein analysis or screening, ultrasonography, amniocentesis, and chorionic villus sampling.

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 (polyhydramnios). An unusually small placenta may be noted during the birth of the child.