Unlike Down syndrome, which also is caused by an extra chromosome, the developmental issues caused by Trisomy 18 are associated with more medical complications that are more potentially life-threatening in the early months and years of life.
Studies have also shown that only 50% of babies who are carried to term will be born alive, and baby girls will have higher rates of live birth than baby boys.
Some infants will be able to survive to be discharged from the hospital with home nursing support to assist with care by the parents.
Only 10 percent or more may survive to their first birthdays
But even then there are children with Trisomy 18 that can enjoy many years of life with their families, reaching milestones and being involved with their community.
A small number of adults (usually girls) with Trisomy 18 have and are living into their twenties and thirties, but have significant developmental delays that do not allow them to live independently without full time caregiving.
Individuals with trisomy 18 often have slow growth before birth (intrauterine growth retardation) and a low birth weight.
Affected individuals may have heart defects and abnormalities of other organs that develop before birth.
Other features of trisomy 18 include a small, abnormally shaped head; a small jaw and mouth; and clenched fists with overlapping fingers.
(also look at Exams and Tests for other Symptoms)
Trisomy 18 occurs in about 1 in 5,000 live-born infants; it is more common in pregnancy, but many affected fetuses do not survive to term.
Although women of all ages can have a child with trisomy 18, the chance of having a child with this condition increases as a woman gets older.
The Genetic Changes That Causes it
Most cases of trisomy 18 result from having three copies of chromosome 18 in each cell in the body instead of the usual two copies.
The extra genetic material disrupts the normal course of development, causing the characteristic features of trisomy 18.
Approximately 5 percent of people with trisomy 18 have an extra copy of chromosome 18 in only some of the body's cells.
In these people, the condition is called mosaic trisomy 18. The severity of mosaic trisomy 18 depends on the type and number of cells that have the extra chromosome.
The development of individuals with this form of trisomy 18 may range from normal to severely affected.
Very rarely, part of the long (q) arm of chromosome 18 becomes attached (translocated) to another chromosome during the formation of reproductive cells (eggs and sperm) or very early in embryonic development.
Affected individuals have two copies of chromosome 18, plus the extra material from chromosome 18 attached to another chromosome.
People with this genetic change are said to have partial trisomy 18.
If only part of the q arm is present in three copies, the physical signs of partial trisomy 18 may be less severe than those typically seen in trisomy 18.
If the entire q arm is present in three copies, individuals may be as severely affected as if they had three full copies of chromosome 18.
Exams and Tests
An exam during pregnancy may show an unusually large uterus and extra amniotic fluid.
There may be an unusually small placenta when the baby is born. A physical exam of the infant may show unusual fingerprint patterns.
X-rays may show a short breast bone.
Chromosome studies will show trisomy 18. The chromosome abnormality may be present in every cell or present in only a certain percentage of the cells (called mosaicism).
Studies may also show part of the chromosome in some cells. Rarely, part of the chromosome 18 becomes attached to another chromosome. This is called translocation.
Other signs include:
Hole, split, or cleft in the iris of the eye (coloboma)
Separation between the left and right side of the abdominal muscle (diastasis recti)
Umbilical hernia or inguinal hernia
There are often signs of congenital heart disease, such as:
Atrial septal defect (ASD)
Patent ductus arteriosus (PDA)
Ventricular septal defect (VSD)
Tests may also show kidney problems, including:
Diagnostic & Management
Sadly there is no way to cure it, you can only really do genetic testing if there are noticeable symptoms.