Trisomy 18

Trisomy 17-18 2

Trisomy 18, also known as Edwards syndrome, is a chromosomal disorder characterized by the presence of an extra copy of chromosome 18, instead of the usual two copies. This condition is a type of aneuploidy, which refers to an abnormal number of chromosomes in a cell. Trisomy 18 is the second most common trisomy after Trisomy 21 (Down syndrome). It was first described by John Hilton Edwards in 1960, hence the name Edwards syndrome.

Causes and Diagnosis

Trisomy 18 is caused by a nondisjunction event that occurs during the formation of gametes (egg or sperm cells). This results in an egg or sperm cell having an extra chromosome 18, which, when fertilized, leads to an embryo with three copies of chromosome 18. The condition can be diagnosed prenatally through genetic testing methods such as amniocentesis, chorionic villus sampling (CVS), and non-invasive prenatal testing (NIPT). Postnatal diagnosis involves karyotyping and fluorescence in situ hybridization (FISH) tests to confirm the presence of the extra chromosome.

Symptoms and Prognosis

Infants with Trisomy 18 often have a low birth weight, small jaw (micrognathia), clenched fists with overlapping fingers, and low-set ears. They may also have congenital heart defects, kidney problems, and other organ abnormalities. Developmental delays and intellectual disability are common. Unfortunately, the prognosis for children with Trisomy 18 is poor, with many infants dying within their first year of life due to complications related to their severe physical and mental abnormalities. However, some children with Trisomy 18 live into their teenage years and beyond, albeit with significant health and developmental challenges.

Management and Support

There is no cure for Trisomy 18, and management focuses on providing supportive care to improve the quality of life for affected individuals. This may include surgeries to correct physical abnormalities, therapies to address developmental delays, and palliative care. Support groups and counseling are also important for families to cope with the emotional and practical challenges of caring for a child with Trisomy 18.

Epidemiology

Trisomy 18 affects approximately 1 in 6,000 live births, with a higher incidence in pregnancies of older mothers. However, many affected pregnancies result in miscarriage or stillbirth, so the actual number of cases may be higher.

Ethical and Social Considerations

The diagnosis of Trisomy 18 raises complex ethical and social issues, including decisions about pursuing aggressive medical intervention versus palliative care, and the impact of the condition on families. These considerations require sensitive and informed discussions among families, healthcare providers, and ethicists.