Although about one hundred different TWIST1 mutations have been reported in patients with the dominant haploinsufficiency Saethre-Chotzen syndrome (typically associated with craniosynostosis), substitutions uniquely affecting the Glu117 codon were not observed previously.
To date, our detection rate for TWIST or FGFR mutations is 68% in our Saethre-Chotzen syndrome patients, including our five patients elsewhere reported with TWIST mutations.
This distance is more significantly altered in FGFR-related brachycephaly syndromes (especially Crouzon and Pfeiffer syndromes), than Saethre-Chotzen syndrome (TWIST1 mutation) and isolated non-syndromic bicoronal synostosis.
The co-localisation of ACS III and TWIST prompted us to screen ACS III patients for TWIST gene mutations especially as mice heterozygous for Twist null mutations displayed skull defects and duplication of hind leg digits.
In addition to 10 different, known mutations in FGFR1,FGFR2 or FGFR3, one novel missense mutation, c.528C>G(p.Ser176Arg), was detected in the TWIST1 gene of a patient with Saethre-Chotzen syndrome.
A specific genetic etiology can be identified in ∼21% of cases, 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 synostosis.
Fibroblasts from 10 individuals each with Apert syndrome (FGFR2 substitution S252W), Muenke syndrome (FGFR3 substitution P250R), Saethre-Chotzen syndrome (various mutations in TWIST1) and non-syndromic sagittal synostosis (no mutation detected) were cultured.
The authors conclude that when using stringent inclusion criteria for studies of Saethre-Chotzen syndrome, patients who have a pathogenic mutation of the TWIST gene should be excluded.
Saethre-Chotzen syndrome is an autosomal dominantly inherited disorder caused by mutations in the twist family basic helix-loop-helix transcription factor 1 (TWIST1) gene.
This is the first demonstration that non-coding SNVs of TWIST1 can cause SCS, and highlights the importance of screening the 5' UTR in clinically diagnosed SCS patients without a coding mutation.
We have identified Twist target genes using human mutant calvaria osteoblastic cells from a child with Saethre-Chotzen syndrome with a Twist mutation that introduces a stop codon upstream of the bHLH domain.