PE29.1-3 | Down Syndrome — Summary & Reflection

KEY TAKEAWAYS

Down syndrome (trisomy 21) is the most common chromosomal cause of intellectual disability, occurring in ~1 in 700–1000 live births. Three cytogenetic mechanisms exist: free trisomy 21 (~95%, meiotic non-disjunction, karyotype 47,+21, recurrence ~1% + age risk); robertsonian translocation (~4%, karyotype 46 with t(14;21), recurrence 10–15% if maternal carrier, 2–5% if paternal, 100% if t(21;21)); and mosaicism (~1%, post-zygotic, milder phenotype, recurrence ~1%). Clinical features include upslanting palpebral fissures, epicanthal folds, hypotonia, intellectual disability, and single palmar crease. Major complications: AVSD (~40–50% of CHD), duodenal atresia, atlantoaxial instability, hypothyroidism, and ALL (20× increased risk). Diagnosis is by karyotype; prenatal screening uses first-trimester combined screen (NT + PAPP-A + β-hCG) or cfDNA. Management is multidisciplinary — cardiac surgery (early, before pulmonary hypertension), early intervention, surveillance protocol, and inclusive education. Genetic counselling must always be mechanism-specific; quoting blanket recurrence risk without a karyotype is an error.

REFLECT

Recall the family from the opening hook. Having worked through this module, consider: How would you structure the conversation with those parents about their 2-day-old baby? What would you say first — the diagnosis, the heart defect, the development, or the recurrence risk? Which piece of information would be most important to them in that moment, and which should be deferred? Reflect on how the cytogenetic mechanism (which you do not yet know in the hook scenario) will change the recurrence counselling — and why ordering the karyotype is not just a diagnostic step but a counselling prerequisite. Write a 3-sentence reflective note in your learning journal on what you think the hardest part of this counselling conversation would be and how you plan to prepare for it.