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Trisomy 13, also known as Patau syndrome, is a severe chromosomal disorder caused by the presence of an extra copy of chromosome 13. It leads to multiple congenital anomalies, particularly affecting the central nervous system, face, heart, and limbs, and is associated with high neonatal mortality.
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https://www.youtube.com/watch?v=QBussteAbA0
Genetics
| Feature |
Description |
| Karyotype |
47,XX,+13 or 47,XY,+13 in full trisomy |
| Mechanisms |
• Full trisomy 13 (~75%) |
| • Mosaicism (~5%) – milder phenotype |
|
| • Unbalanced translocation (~20%) – may recur in families |
|
| Recurrence risk |
Low for full trisomy; higher for translocation carriers |
Epidemiology
| Feature |
Description |
| Incidence |
~1 in 10,000–16,000 live births |
| Sex |
Equal male-to-female ratio |
| Risk factor |
Advanced maternal age increases risk |
Clinical Features
| Domain |
Features |
| Craniofacial |
• Microphthalmia or anophthalmia |
| • Cleft lip and/or palate |
|
| • Microcephaly |
|
| • Scalp defects (aplasia cutis) |
|
| • Low-set malformed ears |
|
| • ‣ |
|
| CNS |
• ‣ (classic finding) |
| • Seizures |
|
| • Severe intellectual disability |
|
| • Hypotonia |
|
| CVS |
Congenital heart defects in >80% |
| • Ventricular septal defect (VSD) |
|
| • Atrial septal defect (ASD) |
|
| • Patent ductus arteriosus (PDA) |
|
| • Dextrocardia |
|
| Limb Anomalies |
• Postaxial polydactyly (extra digit on ulnar side) |
| • ‣ |
|
| • Overlapping fingers |
|
| • Clenched hands |
|
| Genitourinary |
• Cryptorchidism |
| • Hydronephrosis |
|
| • Polycystic kidneys |
|
| • Uterine anomalies |
|
| Growth |
• ‣ |
| • Poor postnatal weight gain |
|
4. Prenatal Diagnosis
| Modality |
Findings |
| Ultrasound |
• Holoprosencephaly (alobar/semi-lobar) |
| • Facial clefts |
|
| • Polydactyly |
|
| • IUGR |
|
| • Cardiac anomalies |
|
| • Omphalocele |
|
| • Single umbilical artery |
|
| Noninvasive screening (NIPT) |
Can detect trisomy 13 from maternal blood |
| Confirmatory tests |
Chorionic villus sampling (CVS) or amniocentesis with karyotyping or FISH |
Radiology
| Modality |
Imaging features |
| Brain (CT/MR) |
• Holoprosencephaly: Failure of prosencephalon to divide; alobar is most severe |
| • Ventriculomegaly: Often present |
|
| • Midline facial defects: Cleft lip/palate, hypotelorism |
|
| Echo |
Structural cardiac anomalies (VSD, ASD, PDA) |
| Skeletal (XR) |
Polydactyly, overlapping digits, short long bones |
Differentials
| Condition |
Distinguishing Features |
| Trisomy 18 (Edwards syndrome) |
Prominent occiput, clenched fists, no polydactyly |
| Smith–Lemli–Opitz syndrome |
Cholesterol synthesis defect, 2nd–3rd toe syndactyly |
| ‣ |
Occipital encephalocele, cystic kidneys, polydactyly (but autosomal recessive) |