Trisomy 18 Syndrome

Trisomy 18 Syndrome, also known as Edwards syndrome, stems from a glitch in your chromosomes, those tiny structures inside cells that harbor genes – the blueprints for making each part of a baby’s body. Named after the doctor who first identified it, this condition arises when there are three copies of chromosome 18 instead of the usual two in the body’s cells.

When an egg and sperm unite to form an embryo, their chromosomes mingle. Each baby typically inherits 23 chromosomes from the mother’s egg and 23 from the father’s sperm, making a total of 46. However, sometimes, either the egg or sperm may carry an incorrect number of chromosomes. If this happens and fertilization occurs, the mistake gets passed on to the developing baby.

In the case of trisomy 18, the term “trisomy” denotes an extra chromosome present in some or all of the body’s cells. For instance, in trisomy 18, the baby ends up with three copies of chromosome 18, leading to abnormal development in many of the baby’s organs.

Types

1. Full trisomy 18: This occurs when there is an extra chromosome 18 in every cell of the baby’s body. It’s the most common type of trisomy 18.
2. Partial trisomy 18: In this type, the child possesses only a portion of an extra chromosome 18. This additional segment may be attached to another chromosome in the egg or sperm, a condition known as translocation. Partial trisomy 18 is exceedingly rare.
3. Mosaic trisomy 18: Here, the extra chromosome 18 is present in only some of the baby’s cells. This form of trisomy 18 is also uncommon.

Prevalence of Trisomy 18

Trisomy 18 ranks as the second most prevalent trisomy syndrome, following trisomy 21 (Down syndrome). Approximately 1 in every 5,000 babies are born with trisomy 18, with a majority being female. However, the actual incidence might be higher as many babies with trisomy 18 do not survive beyond the second or third trimester of pregnancy.

Symptoms of Trisomy 18

Babies with trisomy 18 typically exhibit various serious health issues and physical abnormalities, including:

• Cleft palate
• Clenched fists with overlapping fingers that are difficult to straighten
• Lung, kidney, and stomach/intestinal defects
• Rocker-bottom feet deformity
• Feeding difficulties
• Heart defects such as atrial septal defect or ventricular septal defect
• Low-set ears
• Severe developmental delays and intellectual disabilities
• Chest deformity
• Slow growth
• Microcephaly (small head)
• Micrognathia (small jaw)
• Weak cry

Risk Factors for Trisomy 18

The likelihood of having a child with trisomy 18 escalates with the mother’s age, although women of any age can give birth to a baby with this condition. Unfortunately, there are no preventive measures to reduce the chances of having a child with trisomy 18 since it results from a chromosomal disorder.

If you’ve previously had a baby with trisomy 18, the risk of having another one is between 0.5% to 1%. However, if you or your partner carries a chromosome disorder predisposing to partial trisomy 18, the risk of recurrence could soar up to 20%.

Diagnosis of Trisomy 18

Initially, doctors typically conduct a screening test using the mother’s blood to assess the risk of trisomy 18 and other diseases stemming from chromosome abnormalities. Although this test cannot provide a definitive diagnosis, it indicates whether the baby is at risk.

To confirm trisomy 18, the doctor performs procedures like amniocentesis or chorionic villus sampling (CVS), where cells from the amniotic fluid or placenta are extracted and analyzed for chromosomal abnormalities. These tests are usually conducted following the screening test, bearing in mind their slight risk of causing miscarriage or premature labor.

CVS, conducted in the first trimester, and amniocentesis, performed in the second or third trimester, aid in diagnosing trisomy 18.

Trisomy 18 Ultrasound

Around the 12th week of pregnancy or later, an ultrasound scan provides visual insights into the fetus’s condition. Although it may offer clues about trisomy 18, the diagnosis is typically confirmed through CVS or amniocentesis. Ultrasound findings indicative of trisomy 18 may include smaller size, intestinal issues, and limb abnormalities like clenched fists.

Following birth, the doctor may suspect trisomy 18 based on the baby’s facial and bodily features. A blood sample is then taken to confirm the chromosomal disorder.

Additionally, the chromosome blood test assists in gauging the likelihood of having another child with trisomy 18. Concerned parents, particularly those with a history of trisomy 18 in a previous pregnancy, may seek guidance from a genetic counselor.

Treatments

Trisomy 18 cannot be cured, and treatment primarily revolves around providing supportive medical care to enhance the child’s quality of life. This may involve:

1. Surgeries, particularly for correcting heart defects.
2. Administration of medications.
3. Utilization of feeding tubes for proper nutrition.
4. Use of breathing tubes to assist with respiration.
5. Focus on comfort care rather than aggressive treatments.

Previously, babies born with trisomy 18 weren’t typically resuscitated at birth due to bleak long-term survival prospects. However, current guidelines have evolved, and resuscitation of infants with trisomy 18 is now more commonplace. The Textbook of Neonatal Resuscitation has revised its stance, no longer categorizing trisomy 18 as a condition where non-resuscitation at birth is ethically acceptable.

Life Expectancy

Due to the severe physical defects associated with trisomy 18, many affected babies do not survive to birth. Approximately half of full-term pregnancies end in stillbirth, with boys being more susceptible than girls. Among those who are born alive, half pass away within the first week of life, and less than 10% celebrate their first birthday. Those who do surpass this milestone often face significant health challenges necessitating extensive care. Only a tiny fraction of individuals with trisomy 18 reach their 20s or 30s.

Emotional Support and Resources

Coping with the challenges of having a child with trisomy 18 can be overwhelming for parents. Seeking support from organizations like the Chromosome 18 Registry & Research Society and the Trisomy 18 Foundation can provide invaluable assistance during this trying period.

Trisomy 13

Trisomy 13, also known as Patau syndrome, is another chromosomal anomaly where the individual possesses three copies of chromosome 13 instead of the usual two. Similar to trisomy 18, trisomy 13 can manifest in various forms, including full trisomy, partial trisomy (via translocation), or mosaic trisomy.

Babies with trisomy 13 typically exhibit severe medical complications and birth defects, such as heart abnormalities, spinal cord and brain disorders, cleft lip and/or palate, microphthalmia (underdeveloped eyes), extra digits, hypotonia (weak muscle tone), and abdominal organs protruding through the umbilical cord opening.

Trisomy 13 affects approximately 1 in 16,000 births, with a majority of affected fetuses not surviving beyond the third trimester. Most infants born with trisomy 13 succumb to medical complications within days or weeks of birth, with only a small percentage surviving past their first year. While maternal age increases the risk, women of any age can have a child with trisomy 13. Diagnosis can occur before or after birth through similar testing methods used for trisomy 18 detection.

Key Points about Trisomy 18

1. Trisomy 18 involves having three copies of chromosome 18 in the body’s cells instead of the usual two, leading to severe physical and mental disabilities.
2. There is no cure for trisomy 18, but treatment options include surgeries, medications, breathing tubes, feeding tubes, or opting for comfort care.
3. Life expectancy for individuals with trisomy 18 is typically a year or less.

FAQs

1. How old is the oldest living person with trisomy 18?
   • The oldest reported individuals were in their early 40s a few years ago, but their current status is uncertain.
2. Are babies with trisomy 18 less active in the womb?
   • Yes, they often exhibit reduced activity in the womb.

Sources

• March of Dimes
• Trisomy 18 Foundation
• National Institutes of Health Genetics Home Reference
• Merck Manual Professional
• Lucille Packard Children’s Hospital at Stanford
• Rumack, Carol M. Diagnostic Ultrasound
• StatPearls
• California Prenatal Screening Program
• Facts, Views and Vision in ObGyn
• Cincinnati Children’s Hospital
• Sudanese Journal of Paediatrics
• Children’s Hospital of Philadelphia