Clinical Scenario:
A newborn has severe congenital anomalies including cleft lip and palate, postaxial polydactyly, microphthalmia, and a ventricular septal defect. A scalp defect is also noted on examination. Cytogenetic testing confirms an additional chromosome 13.
Which of the following statements is most accurate regarding this condition?
A. It is usually caused by a balanced chromosomal translocation
B. It is usually caused by meiotic nondisjunction and is associated with advanced maternal age
C. It is caused by a 22q11.2 microdeletion
D. It predominantly affects males because of X-linked inheritance
E. Most affected infants survive beyond the first year
Correct answer & Explanation:
Answer: B. It is usually caused by meiotic nondisjunction and is associated with advanced maternal age
Explanation
The combination of cleft lip/palate, polydactyly, microphthalmia, scalp defects, and congenital heart disease is characteristic of trisomy 13 (Patau syndrome).
Most cases result from meiotic nondisjunction, producing a full extra chromosome 13. As with other autosomal trisomies, the risk increases with advanced maternal age.
A smaller proportion of cases result from Robertsonian translocations, which have important implications for recurrence risk.
Trisomy 13 is associated with severe multisystem abnormalities and very high infant mortality; only a minority of affected infants survive beyond the first year.
Exam pearl:
Trisomy 13 → Patau syndrome → cleft lip/palate + polydactyly + microphthalmia + severe congenital anomalies.
