Saethre-Chotzen syndrome
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A child has unilateral coronal craniosynostosis (anterior plagiocephaly), low-set frontal hairline, ptosis, and a broad great toe. Hands show partial cutaneous syndactyly between the second and third fingers. Father has a similar facial gestalt and was diagnosed as an adult.
AD; TWIST1 (basic helix-loop-helix transcription factor) on 7p21. Loss-of-function mechanism:
- Sequence variants (~70%): missense, nonsense, frameshift in the bHLH domain
- Whole-gene deletions (~25%): detectable by CMA or MLPA, often associated with intellectual disability when contiguous neighboring genes are deleted
Penetrance is essentially complete but expressivity is highly variable; many parents identified retroactively after a child is diagnosed.
- Coronal craniosynostosis: uni- or bilateral; bilateral gives brachycephaly, unilateral gives anterior plagiocephaly
- Low-set frontal hairline: consistent finding, helps distinguish
- Ptosis: bilateral, often mild
- Facial asymmetry in unilateral cases
- Ear anomalies: small with prominent crus
- Limb findings: mild cutaneous syndactyly (fingers 2-3, toes 2-3); broad great toes; partial polydactyly possible
- Intellectual disability uncommon in sequence variants; more common with whole-gene deletions
- Hearing loss; cleft palate (less common)
- Clinical (craniosynostosis + low frontal hairline + ptosis + mild syndactyly is highly suggestive)
- 3D CT skull
- TWIST1 sequencing AND deletion analysis (MLPA or CMA); must rule out the deletion form
- Examine parents; variable expressivity means a parent may have only mild facial features
- Crouzon syndrome (FGFR2): craniosynostosis + midface hypoplasia + proptosis; no syndactyly, no ptosis pattern
- Pfeiffer syndrome (FGFR1, FGFR2): craniosynostosis + broad thumbs/great toes + syndactyly. Classic Pfeiffer thumb is broader and more deviated than Saethre-Chotzen.
- Apert syndrome (FGFR2): craniosynostosis + severe complex syndactyly
- Muenke syndrome (FGFR3 P250R): uni-/bicoronal synostosis + mild limb findings; sensorineural hearing loss prominent
- Carpenter syndrome (RAB23): multisuture craniosynostosis + polysyndactyly; AR
- Antley-Bixler: craniosynostosis + radiohumeral synostosis
- Cranial vault remodeling in infancy/early childhood (same surgical timing as other craniosynostoses)
- Ophthalmology: ptosis correction, refractive errors
- Audiology baseline + monitoring
- Hand/foot surgery as needed for syndactyly
- Developmental: screen all patients, especially those with whole-gene deletions
- AD with ~50% recurrence; offer parental testing and prenatal diagnosis once a familial variant is known
"Saethre-Chotzen = Skull (synostosis) + Subtle hairline (low frontal) + Subtle syndactyly": three S's that capture the gestalt.
The low frontal hairline is a useful tiebreaker between Saethre-Chotzen and the FGFR-related craniosynostoses (Crouzon, Pfeiffer, Apert, Muenke). When you see hair starting close to the eyebrows, TWIST1 moves up the differential.