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Edwards syndrome
Also known as Trisomy 18 · 47,XX,+18 · 47,XY,+18
Affected individuals typically experience significant health issues, including severe intellectual disabilities and characteristic physical features. It affects approximately 1 in 5,000 live births and is a major cause of early mortality due to complex medical needs.
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Overview
Edwards syndrome, commonly known as Trisomy 18, is a serious genetic condition caused by the presence of an extra copy of chromosome 18. Instead of the usual two copies, individuals with Edwards syndrome have three copies of chromosome 18 in each cell. This additional genetic material significantly disrupts normal development, leading to a range of severe health challenges. It is one of the more common trisomies to result in live births, following Down syndrome (Trisomy 21). The condition affects roughly 1 in 5,000 live births [PMID:33671239].
The majority of cases of Edwards syndrome are not inherited. They arise spontaneously during the formation of reproductive cells (eggs or sperm) or very early in foetal development. The severity of the condition can vary slightly depending on whether all cells have the extra chromosome (full Trisomy 18) or only some cells are affected (mosaic Trisomy 18), though most cases are full Trisomy 18 with severe impacts.
Symptoms & clinical features
Individuals with Edwards syndrome often present with a distinctive pattern of features and severe health problems impacting nearly every organ system. Common physical characteristics include a small head (microcephaly), small jaw (micrognathia), and low-set, malformed ears. A clenched hand with overlapping fingers is a very typical presentation, along with 'rocker-bottom' feet [PMID:17950790].
Beyond these physical signs, there are often serious internal organ abnormalities. These frequently include heart defects, kidney abnormalities, and problems with the digestive system. Severe developmental delay and intellectual disability are consistently observed. Feeding difficulties, breathing problems, and growth restriction are also common challenges, contributing to the complexity of care required for individuals with Edwards syndrome.
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Affected organs
Edwards syndrome can profoundly affect multiple organ systems throughout the body. The heart is frequently impacted, with many individuals born with complex congenital heart defects. The kidneys may show structural abnormalities, and defects of the gastrointestinal system, such as an omphalocele (abdominal organs protruding through the umbilical cord), are also observed. The central nervous system is significantly affected, leading to intellectual disability and developmental delays.
Skeletal abnormalities are also common, including characteristic hand and foot formations. Respiratory issues and feeding difficulties can stem from a combination of structural problems and neurological impairment. This broad involvement of essential organ systems underscores the serious health challenges associated with Trisomy 18.
Risks & severity
Edwards syndrome is typically a very severe condition. The majority of affected pregnancies sadly result in miscarriage or stillbirth. For live births, the prognosis is often poor, with around 50% of infants not surviving beyond the first week of life, and only about 5-10% living past their first birthday [PMID:28779693]. Survival beyond infancy is rare, though some individuals can live into childhood or beyond, particularly those with mosaic forms of the condition.
The severity of health problems varies among individuals, but significant developmental delays, intellectual disability, and serious medical complications are almost always present. Management focuses on supportive care to address the complex medical needs, improve quality of life, and manage symptoms. While the average life expectancy is short, ongoing research and improved medical care may lead to incremental improvements in outcomes for some children.
Genetic causes
Edwards syndrome is primarily caused by the presence of an extra copy of chromosome 18. This is referred to as Trisomy 18. In most cases (about 90%), this extra chromosome arises randomly during the formation of egg or sperm cells. This is known as a de novo event, meaning it is not inherited from a parent but occurs spontaneously [PMID:33671239].
In some less common instances, Edwards syndrome can occur due to a translocation where a piece of chromosome 18 becomes attached to another chromosome. While rare, a balanced translocation in a parent can increase the risk of having a child with Trisomy 18 in subsequent pregnancies. The genes SMAD4 and TGIF1 are located on chromosome 18, and although their direct roles in the specific features of Edwards syndrome are complex, having an extra copy of these and many other genes on chromosome 18 disrupts the delicate balance required for normal development.
- SMAD4 SMAD family member 4The SMAD4 gene provides instructions for a protein crucial in cellular signalling, regulating cell growth and division, and acting as a tumour suppressor.
- TGIF1 TGFB induced factor homeobox 1
Inheritance pattern
Edwards syndrome is almost always a sporadic (non-inherited) condition, meaning it typically occurs randomly and is not passed down through families. The presence of an extra chromosome 18 usually arises from an error during cell division in the egg or sperm, or shortly after conception. This is known as non-disjunction, where chromosomes fail to separate properly.
In rare cases (about 5-10%), Edwards syndrome can be caused by a 'translocation'. This is where part of chromosome 18 gets attached to another chromosome. If a parent carries a 'balanced translocation' - meaning they have the rearranged genetic material but no missing or extra DNA - they are usually healthy but have an increased risk of having a child with an unbalanced translocation, leading to conditions like Edwards syndrome. Genetic counselling is important in such cases to understand the specific risks for future pregnancies.
Diagnosis & testing
Edwards syndrome is often suspected during pregnancy based on prenatal screening tests. This might include a combined test (blood test and ultrasound scan in the first trimester) or the quadruple test (blood test in the second trimester), which can indicate an increased risk. Non-invasive prenatal testing (NIPT), which analyses cell-free DNA from the mother's blood, can also provide a strong indication of Trisomy 18 [PMID:33671239]. However, these are screening tests, meaning they indicate risk rather than providing a definite diagnosis.
A definitive diagnosis of Edwards syndrome requires a chromosomal analysis, typically through diagnostic procedures such as chorionic villus sampling (CVS) or amniocentesis during pregnancy. After birth, a diagnosis can be confirmed by a blood test for karotyping or a chromosomal microarray analysis (CMA). In the UK, genetic testing for suspected chromosomal conditions like Edwards syndrome falls under the NHS Genomic Medicine Service (GMS) framework. Referrals for these tests are generally made by obstetricians, paediatricians, or clinical geneticists, aligning with relevant R-codes for rare disease testing.
Management & lifestyle
The management of Edwards syndrome is highly individualised and focusses on supportive care to address the complex medical needs and improve comfort. This typically involves a multidisciplinary team of specialists, including paediatricians, cardiologists, neurologists, and geneticists. Treatment plans focus on managing symptoms and complications, rather than curing the underlying genetic cause.
Care often includes interventions for feeding difficulties, respiratory support, and management of heart and kidney problems. Regular monitoring for potential complications is essential. In the UK, families can access support through the NHS, including specialist clinics, palliative care services, and genetic counselling. Genetic counsellors offer crucial support, providing information about the condition, discussing prognosis, and helping families navigate difficult decisions. It is important to discuss all aspects of care with healthcare professionals.
UK care pathway
In the UK, suspected cases of Edwards syndrome are managed within the NHS Genomic Medicine Service (GMS) pathways. If screening tests suggest a high risk, patients are generally referred to a foetal medicine specialist or clinical geneticist for diagnostic testing. Confirmatory genetic testing, such as karyotyping or chromosomal microarray, is offered through NHS Genomic Laboratory Hubs, often using specific R-codes for rare disease diagnoses.
Following a confirmed diagnosis, individuals and their families will typically be supported by a clinical genetics team. This team provides comprehensive counselling, discussing the condition's implications and helping to coordinate care. Genetic counsellors play a vital role in explaining inheritance patterns, recurrence risks, and directing families to appropriate support networks and medical specialists.
Frequently asked questions
Is Edwards syndrome inherited?
In most cases, Edwards syndrome is not inherited. It usually results from a random error during egg or sperm formation. Very rarely, it can be linked to a parental 'balanced translocation', which a genetic counsellor can explain.
What is the life expectancy for someone with Edwards syndrome?
Edwards syndrome is a very severe condition. Sadly, many affected pregnancies do not result in live birth. For those born, approximately half do not survive beyond their first week, and only about 5-10% live past their first birthday. Survival into childhood is rare, though not impossible.
Can Edwards syndrome be detected during pregnancy?
Yes, Edwards syndrome can often be suspected through routine prenatal screening tests like blood tests and ultrasound scans. A definitive diagnosis requires further diagnostic tests such as chorionic villus sampling (CVS) or amniocentesis, which analyse the baby's chromosomes.
What kind of support is available for families affected by Edwards syndrome?
Families in the UK can access support through the NHS, including specialist paediatric care, palliative care services, and genetic counselling. Support groups and charities also provide valuable resources, advice, and a community for affected families.
Are there different types of Edwards syndrome?
Yes, the most common type is 'full Trisomy 18', where every cell has an extra chromosome 18. Less commonly, individuals can have 'mosaic Trisomy 18', where only some cells have the extra chromosome. There's also 'partial Trisomy 18' where only part of the chromosome is duplicated, often due to a translocation.
References
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- Balasundaram P, Avulakunta ID. Trisomy 18 (Edwards Syndrome). 2026. PMID: 34033359
- Crawford D, Dearmun A. Edwards' syndrome. Nursing children and young people. 2016. PMID: 27927129
- Goel N, Morris JK, Tucker D. Trisomy 13 and 18-Prevalence and mortality-A multi-registry population based analysis. American journal of medical genetics. Part A. 2019. PMID: 31566869
- Boddupally K, Rani Thuraka E. Artificial intelligence for prenatal chromosome analysis. Clinica chimica acta; international journal of clinical chemistry. 2024. PMID: 38007058
- James AE Jr, Belcourt CL, Atkins L. Trisomy 18. Radiology. 1969. PMID: 4236175
- Anderson NG, Smithurst B, Regius Mary Sister. Trisomy 18. Lancet (London, England). 1970. PMID: 4098378