Craniosynostosis, the premature fusion of the cranial sutures, is a heterogeneous disorder with a prevalence of ~1 in 2,200 (refs. 1,2). A specific genetic etiology can be identified in ~21% of cases3, including mutations of TWIST1, which encodes a class II basic helix-loop-helix (bHLH) transcription factor, and causes Saethre-Chotzen syndrome, typically associated with coronal synostosis4-6. Starting with an exome sequencing screen, we identified 38 heterozygous TCF12 mutations in 347 samples from unrelated individuals with craniosynostosis. The mutations predominantly occurred in patients with coronal synostosis and accounted for 32% and 10% of subjects with bilateral and unilateral pathology, respectively. TCF12 encodes one of three class I E-proteins that heterodimerize with class II bHLH proteins such as TWIST1. We show that TCF12 and TWIST1 act synergistically in a transactivation assay, and that mice doubly heterozygous for loss-of-function mutations in Tcf12 and Twist1 exhibit severe coronal synostosis. Hence, the dosage of TCF12/TWIST1 heterodimers is critical for coronal suture development.

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The low complication rates and the excellent functional outcomes make the anterolateral thigh flap in combination with a salivary bypass tube a viable option for reconstruction of these difficult defects.