Mutations in 12 genes lead to syndromal conditions with craniosynostosis as the main symptom: FGFR1 (fibroblast growth factor receptor 1), FGFR2 (fibroblast growth factor receptor 2), FGFR3 (fibroblast growth factor receptor 3), TWIST1 (twist homolog [Drosophila] 1), EFNB1 (Ephrin-B1), RAB23 (Ras-related protein), MSX2 (muscle segment homeobox [Drosophila] 2), TGFBR1 (transforming growth factor-ß receptor type 1), TGFBR2 (transforming growth factor-ß receptor type 2), POR (cytochrome P450 oxidoreductase), FBN (fibrillin), and TCF12 (transcription factor 12). Besides these genes, there are numerous others that are more loosely connected with craniosynostosis.
Genetic studies have direct clinical applicability since greater knowledge of the known genetic changes that cause hereditary craniofacial syndromes helps to improve our understanding of the clinical phenotype and prognosis, and provides an opportunity for individualized assessment of the risk of recurrence in the family (genetic counseling).
DNA from 144 out of 150 patients met the quality requirement for undergoing next-generation sequencing analysis. In 89 of the 144 (approximately 62%) patients analyzed, we found known pathogenic, or probably pathogenic, gene variants that can explain the patient’s clinical symptoms. The majority of these variants were found in “classical” craniosynostosis genes, i.e. FGFR2, TWIST1, FGFR3, FGFR1, TCF12, EFNB1, and POR.
We have been able to establish new, previously undescribed variants in the FGFR2 gene (2 new variants), FGFR1 (1 variant), TWIST1 (3 variants), TCF12 (3 variants), and POR (1 variant). These variants meet the criteria for classification as probably pathogenic, and are phenotypically correlated.
Besides pathogenic variants in previously known genes linked to craniosynostosis, we have found pathogenic and probably pathogenic variants in 2 genes (2 patients) whose mutations lead to syndromal conditions with documented craniosynostosis. These were: 1 new probable pathogenic variant in the KMT2D gene, in a patient with clinical Kabuki syndrome type 1 (OMIM [Online Mendelian Inheritance in Man®] # 147920), and 1 previously described pathogenic variant in the SKI gene associated with Shprintzen – Goldberg syndrome (OMIM # 182212).
In addition, in the IL11RA gene (2 patients) we have identified 2 new variants in homozygous form that are associated with craniosynostosis and dental abnormalities (OMIM # 614188). The IL11RA gene may be central to these complex conditions and should therefore be included in a more comprehensive gene panel for craniosynostosis. This knowledge is an example of how research improves the clinical routine for genetic analysis.
In one patient, we found a combination of two genetic changes that both occurred de novo (sporadically): a truncating variant, associated with Kabuki syndrome, in the KMT2D gene and a 3.2 Mbp 10q22.3q23.1 microdeletion, detected by using SNP (single nucleotide polymorphism) array analysis before the mutation screening concerned was performed. This unusual case illustrates the importance of meticulous clinical assessment of patients with craniosynostosis before interpretation of the genetic results, and provides evidence that craniosynostosis is part of the clinical picture in Kabuki syndrome.
In 33 patients out of 144 analyzed (approximately 23%), we have not found any pathogenic, or probably pathogenic, variant in any of the 63 genes sequenced. On the other hand, in these cases we have noted, in a number of genes in the panel, variants of currently unknown clinical significance (VOUS: variant of unknown clinical significance). An in-depth assessment of both the genotype and the patient's phenotype is needed here, in order for the possible disease-causing effect of these variants to be determined.
In 22 out of 144 patients (approximately 15%) analyzed, we found no genetic abnormality at all.
Overall, our initial study showed that a broad genetic screening of craniosynostosis patients has high accuracy (approximately 62%) and simultaneously provides means of explaining the etiology of complex phenotypes that are not among the classic craniosynostosis syndromes. The studies also give unique opportunities to identify new genes and mutations that cause craniosynostosis.
Craniofacial surgery has been performed at the Department of Plastic Surgery for over 40 years. This has made possible long-term monitoring of not only these patients’ surgical outcomes, but also of how their neuropsychological condition, life situation and quality of life develop right up to adulthood. We have previously conducted a couple of questionnaire surveys of two of the syndromal groups. For patients with Apert syndrome, we were able to show that the majority had some form of education and employment, but that their major social problem was the lack of a social network. They were often still living at home with their parents and had few friends. For patients with Crouzon syndrome, the situation in adulthood was generally better. The range of life situations was large, but most lived a relatively full life with education, work and family.
Among patients with isolated synostosis, several studies have been able to show an elevated incidence of disorders in neuropsychological development. Within this group, concentration and learning difficulties, for example, are particularly common in metopic synostosis, but also occur in sagittal synostosis. Studies have shown that surgery for sagittal synostosis enables children to make up for the previously observable delay in their early development, while children with sagittal synostosis who did not undergo surgery were not able to catch up in terms of development. The effect was noticeable over a long period. Other studies have claimed that the more extensive the surgery that is performed, and the earlier it is carried out, the more favorable the outcome is from a developmental point of view. These studies have had a major impact, but have methodological weaknesses.
We have measured full-scale IQ, using the Wechsler Adult Intelligence Scale (WAIS-IV) from 16 years of age and Wechsler Intelligence Scale for Children (WISC-IV) for 6–16-year-olds, in children operated on for craniosynostosis. Our dropout rate is uniquely small, which may be due to the fact that we have called upon patients living in Gothenburg and then expanded the material, step by step, by contacting patients who lived increasingly far away from Sahlgrenska. We have thus avoided nonresponse and dropout due to excessively long journeys. Preliminary results indicate an entirely normal IQ for isolated synostosis, and we have a mean value and a spread of the values that are congruent with the normal distribution. These results deviate from several publications in the field, where mean values for full-scale IQ that are very high, up to 112, are seen — a finding that seems wholly implausible. Either these studies have a large selection bias or the instruments were used incorrectly. Our results indicate that we use the instruments correctly and that our strategy of selecting patients who live a short distance from Sahlgrenska yields a uniquely small selection bias.
A specific test of attention, the Conners Cognitive Performance Test (CPT), has shown several minor deviations from norm data.
General abilities were investigated on the basis of reports from the parents (Adaptive Behavior Assessment System, ABAS), and here too we find minor deviations.
Taken together, these studies show that adolescents who have undergone surgery for sagittal synostosis and metopic synostosis have normal development, but that several minor deviations from the norm are identifiable.