Trisomy 18, also known as Edwards syndrome, is a genetic condition impacting multiple bodily systems. It is associated with significant developmental challenges and a complex array of health issues from birth. Understanding this condition involves recognizing its genetic origins, physical and developmental effects, diagnosis, outlook, and supportive care.
Understanding the Genetic Basis
A karyotype visually represents an individual’s chromosomes, arranged by size and shape, to examine their number and structure. Typical human cells have 46 chromosomes in 23 pairs. Trisomy 18 means an extra, third copy of chromosome 18, totaling 47 chromosomes. This additional genetic material disrupts normal development, causing the condition’s characteristic features and health concerns.
The most frequent cause of Trisomy 18 is nondisjunction, a random error in cell division. This occurs during egg or sperm cell formation when chromosomes fail to separate properly, resulting in a reproductive cell with an extra chromosome 18. When combined with a normal cell, the embryo has three copies of chromosome 18. This sporadic event is not inherited.
Less common forms include Mosaic Trisomy 18 and Translocation Trisomy 18. Mosaic Trisomy 18 occurs when only some body cells have the extra chromosome 18, while others have two copies. This can happen after fertilization, potentially leading to a milder presentation.
Translocation Trisomy 18 is a rare form where a portion of chromosome 18 attaches to another chromosome, usually 14, 15, or 22. It can be inherited from a parent with a balanced translocation, meaning they have the rearranged chromosome without extra genetic material. This form may affect future pregnancies.
Physical and Developmental Characteristics
Individuals with Trisomy 18 present with distinguishing physical characteristics and health challenges affecting nearly every organ system. These include:
- Cardiac defects: ventricular septal defects, atrial septal defects, and patent ductus arteriosus, impacting cardiovascular function.
- Kidney abnormalities: such as horseshoe kidneys or hydronephrosis, potentially affecting renal function.
- Skeletal issues: including micrognathia (small jaw) and microcephaly (small head).
- Hand abnormalities: clenched hands and overlapping fingers (index over third, fifth over fourth).
- Foot deformities: “rocker-bottom feet” due to a prominent heel and rounded sole.
Feeding difficulties are nearly universal, often requiring specialized interventions like feeding tubes, due to poor suck-swallow coordination or gastrointestinal issues. Growth restriction is pronounced, beginning prenatally and continuing postnatally, resulting in low birth weight and failure to thrive. These children also display significant developmental delays and intellectual disabilities, affecting cognitive and motor milestones.
Many individuals experience respiratory challenges, including apnea and aspiration pneumonia, due to central nervous system dysfunction and structural anomalies. Neurological issues, such as seizures and increased muscle tone, also contribute to care complexity. The specific combination and severity of these features vary considerably among individuals.
Diagnosis and Outlook
Diagnosis of Trisomy 18 can occur prenatally and postnatally. Prenatal screening tests, such as non-invasive prenatal testing (NIPT) or maternal serum screening, indicate increased likelihood. These screenings suggest risk but are not definitive. Confirmation requires diagnostic procedures like chorionic villus sampling (CVS) or amniocentesis.
These diagnostic tests collect fetal cells from the placenta or amniotic fluid, analyzed via karyotype to identify an extra chromosome 18. This chromosomal analysis provides a conclusive diagnosis. Postnatal diagnosis is often prompted by characteristic physical signs at birth, confirmed through a blood test for karyotype analysis.
The outlook for individuals with Trisomy 18 is challenging, with a high mortality rate, particularly within the first year. Approximately half of infants do not survive beyond two weeks, and about 90% do not live past their first birthday. Causes of mortality include severe medical complications like congenital heart defects, respiratory failure, and feeding difficulties leading to malnutrition.
While the prognosis is poor, some individuals, especially those with mosaic Trisomy 18 or less severe complications, may live longer, sometimes into childhood or adolescence. They often require extensive, ongoing medical care to manage complex health needs. Survival variability underscores individualized care plans tailored to each child’s unique presentation and medical challenges.
Supportive Care and Resources
Care for individuals with Trisomy 18 focuses on supportive measures to manage symptoms and enhance quality of life. Medical interventions address specific health issues. For example, surgery may be considered for heart defects, and feeding tubes ensure adequate nutrition for those with severe feeding difficulties.
A multidisciplinary team approach involves specialists. Physical therapy improves motor skills. Occupational therapy assists with daily living activities. Speech therapy addresses communication and feeding issues. These therapies maximize functional abilities and promote comfort.
Family support and counseling are vital. Organizations dedicated to Trisomy 18 provide families with resources, educational materials, and a community of shared experiences. These networks offer emotional support, practical advice, and advocacy, helping families cope with the condition’s unique challenges.
References
Trisomy 18. MedlinePlus. Available at: https://medlineplus.gov/genetics/condition/trisomy-18/. Accessed July 26, 2025.
Edwards Syndrome (Trisomy 18). Cleveland Clinic. Available at: https://my.clevelandclinic.org/health/diseases/22216-edwards-syndrome-trisomy-18. Accessed July 26, 2025.
Trisomy 18. Mayo Clinic. Available at: https://www.mayoclinic.org/diseases-conditions/trisomy-18/diagnosis-treatment/drc-20353846. Accessed July 26, 2025.
Trisomy 18 (Edwards Syndrome). Seattle Children’s. Available at: https://www.seattlechildrens.org/conditions/trisomy-18-edwards-syndrome/. Accessed July 26, 2025.