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Trisomy 18 Syndrome

What is Trisomy 18 Syndrome?

Trisomy 18 Syndrome, also known as Edwards Syndrome, is a chromosomal condition caused by the presence of an extra 18th chromosome in a person’s DNA. Normally, humans have 23 pairs of chromosomes, which include two copies of each chromosome—one inherited from each parent. Individuals with Trisomy 18 have three copies of chromosome 18 instead of the usual two. This genetic anomaly affects the development of the individual, leading to both physical and intellectual disabilities that significantly impact their quality of life.

Causes and Genetic Basis

The primary cause of Trisomy 18 is nondisjunction, an error in cell division during the formation of reproductive cells (sperm or egg). This results in a reproductive cell with an abnormal number of chromosomes. After fertilization, the presence of an extra chromosome 18 disrupts normal development. Additionally, a less common form known as mosaic Trisomy 18 occurs when the extra chromosome is present in only some of the body's cells.

Prevalence and Risk Factors

Trisomy 18 occurs in approximately 1 in 5,000 live births, but the actual incidence might be higher as many pregnancies with Trisomy 18 result in miscarriage. The risk of having a child with this syndrome increases with maternal age, particularly in mothers aged 35 and older. However, it is important to note that this condition can affect anyone, regardless of parental age, race, or health history.

Symptoms and Characteristics

Individuals with Trisomy 18 exhibit a wide array of symptoms that can vary significantly, but there are common characteristics that may be observed:

  • Facial Features: Small head (microcephaly), low-set ears, small jaw (micrognathia), and cleft lip or palate.
  • Limbs and Skeletal Abnormalities: Clenched fists with overlapping fingers, clubfoot, and rocker-bottom feet.
  • Organ Abnormalities: Heart defects are present in over 90% of cases, with ventricular septal defects being the most common. Kidney abnormalities, omphalocele (abdominal wall defects), and esophageal atresia (an interrupted esophagus) are also typical.
  • Growth and Development Issues: Severe developmental delays, intellectual disabilities, and growth retardation are prevalent.
  • Other Conditions: Seizures, vision or hearing difficulties, and feeding issues due to difficulty swallowing or coordinating breathing and sucking.

Diagnosis

The diagnosis of Trisomy 18 can be made prenatally or after birth:

  • Prenatal Screening: Non-invasive methods such as ultrasound can detect physical abnormalities suggestive of Trisomy 18. Additionally, maternal blood tests measure specific biochemical markers.
  • Confirmation Tests: Amniocentesis and Chorionic Villus Sampling (CVS) are more invasive techniques used to confirm the presence of an extra chromosome 18 with a karyotype analysis.
  • Postnatal Diagnosis: A physical examination by a pediatrician, followed by chromosomal analysis, confirms the diagnosis in newborns displaying characteristic symptoms.

Management and Treatment

Currently, there is no cure for Trisomy 18. Management focuses on addressing the individual symptoms to improve the child's quality of life:

  1. Medical Care: Newborns with heart defects and other urgent medical conditions require immediate intervention. However, treatment decisions often depend on the severity of symptoms and the preferences of the family.

  2. Supportive Therapies: Physical, occupational, and speech therapies aim to enhance motor skills and communication. Nutritional support may be necessary to manage feeding issues.

  3. Palliative Care: Given the complex needs of these children, a palliative care team might be involved to provide comfort and support to the child and family.

Prognosis

The prognosis for individuals with Trisomy 18 is often poor. More than 90% of infants do not survive past their first year. However, the severity of the symptoms may vary, and some individuals survive into their teens and twenties, particularly in cases of mosaic Trisomy 18 where fewer cells are affected.

Support and Resources

Families dealing with a diagnosis of Trisomy 18 often need extensive emotional and practical support. Various organizations provide resources and support:

  • Support Groups such as SOFT (Support Organization for Trisomy 18, 13, and Related Disorders) offer community support and information.
  • Genetic Counseling can help families understand the recurrence risk in future pregnancies and explore reproductive options.

Frequently Asked Questions

1. Is Trisomy 18 inherited?
No, Trisomy 18 is typically not inherited. It usually occurs as a random event during the formation of reproductive cells.

2. Can Trisomy 18 be prevented?
While there is no known way to prevent Trisomy 18, parents concerned about genetic risks might consider genetic counseling for information and guidance on reproductive options.

3. How can parents prepare for a child with Trisomy 18?
Parents can prepare by learning about the condition, connecting with support networks, engaging with healthcare professionals early to plan for medical and supportive care needs, and considering genetic counseling for future family planning.

Conclusion

Trisomy 18 Syndrome presents a challenging journey for affected families and individuals. While it poses significant medical and developmental challenges, various interventions can improve the quality of life for those affected. Awareness and access to information, alongside medical and emotional support systems, are vital in managing this condition. Families are encouraged to reach out to relevant organizations and build a network of support to navigate the complexities of living with Trisomy 18.