Trisomy 18 is a chromosomal abnormality. It’s also called Edwards syndrome, after the doctor who first described it.
Chromosomes are the threadlike structures in cells that hold genes. Genes carry the instructions needed to make every part of a baby’s body.
When an egg and sperm join and form an embryo, their chromosomes combine. Each baby gets 23 chromosomes from the mother’s egg and 23 chromosomes from the father’s sperm — 46 in total.
Sometimes the mother’s egg or the father’s sperm contains the wrong number of chromosomes. As the egg and sperm combine, this mistake is passed on to the baby.
A “trisomy” means the baby has an extra chromosome in some or all of the body’s cells. In the case of trisomy 18, the baby has three copies of chromosome 18. This causes many of the baby’s organs to develop in an abnormal way.
There are three types of trisomy 18:
Full trisomy 18. Theextra chromosome is in every cell in the baby’s body. This is by far the most common type of trisomy 18.
Partial trisomy 18. The child has only part of an extra chromosome 18. That extra part may be attached to another chromosome in the egg or sperm (called a translocation). This type of trisomy 18 is scarce.
Mosaic trisomy 18. The extra chromosome 18 is only in some of the baby’s cells. This form of trisomy 18 is also rare.
What Are The Symptoms of Trisomy 18?
Babies with trisomy 18 are often born very small and frail. They typically have many serious health problems and physical defects, including:
- Cleft palate
- Clenched fists with overlapping fingers that are hard to straighten
- Defects of the lungs, kidneys, and stomach/intestines
- Deformed feet (called “rocker-bottom feet” because they’re shaped like the bottom of a rocking chair)
- Feeding problems
- Heart defects, including a hole between the heart’s upper (atrial septal defect) or lower (ventricular septal defect) chambers
- Low-set ears
- Severe developmental delays
- Chest deformity
- Slowed growth
- Small head (microcephaly)
- Small jaw (micrognathia)
- Weak cry
