Paeds · genetics-dysmorphology-and-metabolism
Down syndrome
Also known as Trisomy 21 · Down syndrome · Down's syndrome · 21 trisomy · Mosaic Down syndrome
A fellowship approach to Down syndrome: recognise the three genetic mechanisms (free trisomy 21, Robertsonian translocation, mosaicism) and why a karyotype changes genetic counselling, map the comorbidities by organ system (cardiac, gastrointestinal, endocrine, airway and sleep, haematology, neurodevelopment), and apply an age-stratified health-supervision schedule that is a checklist rather than a single visit.
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Target exams
Red flags
- A hypotonic newborn with flat facies, upslanting palpebral fissures and a single palmar crease is trisomy 21 until the karyotype is back
- An atrioventricular septal defect in an infant can be clinically silent yet cause irreversible pulmonary hypertension if cardiac repair is delayed
- Snoring, restless sleep, daytime somnolence or behavioural change in a child with Down syndrome is obstructive sleep apnea until a sleep study excludes it
- New unsteady gait, neck pain, torticollis, or regression of motor skills raises atlantoaxial instability and warrants cervical spine imaging before any anaesthetic or procedure
- A leukaemoid reaction or abnormal blast count in a Down syndrome neonate is transient abnormal myelopoiesis but mandates haematology review because it carries a leukaemia risk
- Behavioural or cognitive decline in an adult with Down syndrome is early Alzheimer-type dementia until assessed
- Bilious vomiting in the first days of life with a 'double bubble' on abdominal radiograph is duodenal atresia requiring urgent surgical review
Life stages
Care settings
Clinical exam formats
Board mappings
- General and Community Paediatrics
- Growth and Development
- Neonatal Medicine
- General Paediatrics - recognise, investigate and manage chromosomal disorders including Down syndrome
- Cardiology - recognise and manage congenital heart disease
- Child Development and Behaviour - assess and support developmental differences
- Genetics 13-15
- Neonatology 1-3
- Clinical Applications
- Long Cases
- Short Cases
- 1. Neonates and infants with congenital abnormalities
- 2. Genetics: chromosomal and multi-system disorders
- 4. Professional skills and knowledge: Patient management
- Foundation of Practice (FOP)
- Theory and Science (TAS)
- Applied Knowledge in Practice (AKP)
- Clinical
- Development
- Communication
- History
- General Pediatrics Content Outline - D19 Genetics (6%)
- General Pediatrics Content Outline - D18 Neonatology (5%)
- General Pediatrics Content Outline - D13 Cardiology (6%)
- Patient Care 4: Clinical Reasoning
- Patient Care 5: Patient Management
- Medical Knowledge 1: Congenital and Genetic Disorders
- Systems-Based Practice 1: Patient Safety
- Medical Expert
- Pediatrics: Foundations EPA #8 - Communicating assessment findings and management plans to patients and/or families
- Pediatrics: Genetics and Metabolism
A newborn is noted on the postnatal ward to be floppier than expected, with a flat facial profile, upslanting palpebral fissures, and a single transverse palmar crease. The same baby may also have a heart murmur that is hard to hear, a duodenum that never opened, or a blood count crowded with blasts. The fellowship task is not to name the syndrome — the face and the hypotonia do that — but to anticipate, system by system, what trisomy 21 is about to do to this child, and to lay a surveillance net that catches each complication before it causes irreversible harm. [1] [5]
Down syndrome in one line: three copies of chromosome 21. The high-yield comorbidities sit on T.R.I.S.O.M.Y. — Thyroid (congenital and acquired hypothyroidism), Respiratory and sleep (obstructive sleep apnea in over half), Intellectual disability (usually mild) and Immune dysregulation, Skeletal (atlantoaxial instability, short stature), Ophthalmic and hearing (refractive error, conductive loss), Myeloid (transient abnormal myelopoiesis and leukaemia), and the heart is the Y that frames the whole picture (atrioventricular septal defect). Hold these eight systems and the surveillance falls out naturally. [1] [3]
Overview & Definition
Down syndrome is the recognisable clinical pattern that follows when cells carry a third copy of the long arm of chromosome 21. It is the most common autosomal trisomy compatible with survival beyond infancy, and almost every general paediatrician will care for affected children across their working life. The face, the hypotonia, and the developmental trajectory make the diagnosis suspected at the bedside, but the confirmation is genetic and the confirmation matters — the mechanism determines recurrence risk for the parents and for siblings. [1] [2]
The phenotype is produced by gene-dosage imbalance: the extra copy of around 230 genes on chromosome 21 is overexpressed, and the overexpression of a defined subset drives the recognizable features, the congenital malformations, and the disease susceptibilities. Because the gene dosage is consistent, the comorbidities are predictable, and predictability is what makes a surveillance schedule possible. A fellowship answer that lists features without linking them to the underlying trisomy reads as a catalogue; the gene-dosage link is the teaching that holds the topic together. [1] [5]
The lifespan trajectory has transformed. A child born with Down syndrome in the mid-twentieth century had a life expectancy measured in single figures, dominated by untreated congenital heart disease and infection. Cardiac surgery, antibiotics, inclusion, and structured surveillance have moved life expectancy into the seventh decade, and the population prevalence is now rising because affected children survive into adulthood and old age. The clinical task has shifted accordingly — from keeping the infant alive to guiding a person through seven decades of predictable, preventable, and treatable complications. [4] [6]
References10ShowHide
- [1]Bull MJ. Down Syndrome. N Engl J Med, 2020.PMID 32521135
- [2]Weijerman ME, de Winter JP. Clinical practice. The care of children with Down syndrome. Eur J Pediatr, 2010.PMID 20632187
- [3]Bull MJ Health supervision for children with Down syndrome. Pediatrics, 2011.PMID 21788214
- [4]Bittles AH, Bower C, Hussain R, Glasson EJ. The four ages of Down syndrome. Eur J Public Health, 2007.PMID 16857692
- [5]Hitzler JK, Zipursky A. Origins of leukaemia in children with Down syndrome. Nat Rev Cancer, 2005.PMID 15630411
- [6]Kucik JE, Shin M, Siffel C, Marengo L, Correa A. Trends in survival among children with Down syndrome in 10 regions of the United States. Pediatrics, 2013.PMID 23248222
- [7]Bergström S, Carr H, Petersson G, et al. Trends in congenital heart defects in infants with Down syndrome. Pediatrics, 2016.PMID 27252035
- [8]Maris M, Verhulst S, Wojciechowski M, Van de Heyning P. Sleep problems and obstructive sleep apnea in children with down syndrome, an overwiew. Int J Pediatr Otorhinolaryngol, 2016.PMID 26857307
- [9]Shin M, Besser LM, Kucik JE, et al. Prevalence of Down syndrome among children and adolescents in 10 regions of the United States. Pediatrics, 2009.PMID 19948627
- [10]Van Cleve SN, Cannon S, Cohen WI. Part II: Clinical Practice Guidelines for adolescents and young adults with Down Syndrome: 12 to 21 Years. J Pediatr Health Care, 2006.PMID 16675381