Physiology & Biochemistry · patient case question
What is the most common trisomy compatible with survival to birth?
Patient case: Syndromes recognised at the chair
demo: Paediatric and young adult clinic
chief: Several patients whose facial and dental features point to a recognisable syndrome.
history: One child has bilateral painless expansion of the mandibular angles with an upward gaze, and a father with the same childhood history. Another has downslanting palpebral fissures, malar hypoplasia and malformed external ears. A third has notched, screwdriver-shaped permanent incisors and multicusped first molars. A fourth has a smooth philtrum, a thin upper lip and short palpebral fissures.
meds: None.
findings: Not applicable.
Show answer and explanation
Correct answer: C. Trisomy 21
- A. Trisomy 13, Patau syndrome, is rarer still and likewise has very high early mortality.
- B. Trisomy 18, Edwards syndrome, is far less common and carries a very poor prognosis, with most affected infants dying in the first year.
- C. Correct. Trisomy 21, Down syndrome, is the most common autosomal trisomy, occurring in roughly 1 in 700 live births with incidence rising with maternal age. Dental features include delayed and irregular eruption, hypodontia, microdontia, macroglossia with fissuring, a Class III tendency and markedly increased periodontal disease.
- D. Trisomy 16 is the most frequent trisomy at conception but is uniformly lethal in the first trimester, so it is not seen at birth.
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