Expanding the mutation spectrum in 182 Spanish probands with craniosynostosis: identification and characterization of novel TCF12 variants.

Craniosynostosis, caused by the premature fusion of one or more of the cranial sutures, can be classified into non-syndromic or syndromic and by which sutures are affected. Clinical assignment is a difficult challenge due to the high phenotypic variability observed between syndromes. During routine diagnostics, we screened 182 Spanish craniosynostosis probands, implementing a four-tiered cascade screening of FGFR2, FGFR3, FGFR1, TWIST1 and EFNB1. A total of 43 variants, eight novel, were identified in 113 (62%) patients: 104 (92%) detected in level 1; eight (7%) in level 2 and one (1%) in level 3. We subsequently screened additional genes in the probands with no detected mutation: one duplication of the IHH regulatory region was identified in a patient with craniosynostosis Philadelphia type and five variants, four novel, were identified in the recently described TCF12, in probands with coronal or multisuture affectation. In the 19 Saethre-Chotzen syndrome (SCS) individuals in whom a variant was detected, 15 (79%) carried a TWIST1 variant, whereas four (21%) had a TCF12 variant. Thus, we propose that TCF12 screening should be included for TWIST1 negative SCS patients and in patients where the coronal suture is affected. In summary, a molecular diagnosis was obtained in a total of 119/182 patients (65%), allowing the correct craniosynostosis syndrome classification, aiding genetic counselling and in some cases provided a better planning on how and when surgical intervention should take place and, subsequently the appropriate clinical follow up.

Mild isolated craniosynostosis due to a novel FGFR3 mutation, p.Ala334Thr.

Craniosynostosis is the premature fusion of one or more sutures of the skull, which can be syndromic or isolated. Mutations in FGFR1, FGFR2, or FGFR3, among others, are often responsible for these syndromic cases. The associated of FGFR3 mutations with craniosynostosis has been restricted to three mutations, the common p.Pro250Arg in Muenke syndrome, p.Ala391Glu in Crouzon syndrome with acanthosis nigricans, and p.Pro250Leu identified in a family with isolated craniosynostosis. Other FGFR3 mutations result in various skeletal dysplasias: achondroplasia, hypochondroplasia, and thanatophoric dysplasia. Here, we report a novel mutation in exon 8 (IIIc) of FGFR3, p.Ala334Thr, in a young boy with mild craniosynostosis. The mutation segregated with mild craniosynostosis in the family and was absent in 188 normal controls. Alanine 334 is evolutionarily conserved in vertebrates and is located at the amino terminus of the ßF loop in the FGFR3c isoform. The mutation is predicted to alter the protein tertiary structure which may impair its binding to its ligand, FGF1. The identification of a mutation in these clinically heterogeneous disorders can aid recurrence risk assessments. Although the implementation of a stepwise screening strategy is useful in diagnostics, mutations in unscreened regions of genes associated with craniosynostosis may explain a small proportion of craniosynostosis cases.