Clinicogenetic study of Turkish patients with syndromic craniosynostosis and literature review

Phenotypic variability of syndromic craniosynostosis caused by c.833G > T in FGFR2: Clinical and genetic evaluation of eight patients from a five-generation family

Objective

Craniosynostosis is the result of the early fusion of cranial sutures. Syndromic craniosynostosis includes but not limited by Crouzon syndrome and Pfeiffer syndrome. Considerable phenotypic overlap exists among these syndromes and mutations in FGFR2 may cause different syndromes. This study aims to investigate the explanation of the phenotypic variability via clinical and genetic evaluation for eight patients in a large pedigree.

Methods

For each patient, comprehensive physical examination, cranial plain CT scan with three‐dimensional CT reconstruction (3D‐CT), and eye examinations were conducted. Whole exome sequencing was applied for genetic diagnosis of the proband. Variants were analyzed and interpreted following the ACMG/AMP guidelines. Sanger sequencing was performed to reveal genotypes of all the family members.

Results

A pathogenic variant in the FGFR2 gene, c.833G > T (p.C278F), was identified and proved to be co‐segregate with the disease. Some symptoms of head, hearing, vision, mouth, teeth expressed differently by affected individuals. Nonetheless, all the eight patients manifested core symptoms of Crouzon syndrome without abnormality in the limbs, which could exclude diagnosis of Pfeiffer syndrome.

Conclusion

We have established clinical and genetic diagnosis of Crouzon syndrome for eight patients in a five‐generation Chinese family. Variability of clinical features among these familial patients was slighter than that in previously reported sporadic cases.

Optic canal characteristics in pediatric syndromic craniosynostosis

The aim of this study was to compare optic canal parameters of syndromic craniosynostosis patients with those of normal patients to visit the possibility of optic nerve impingement as a cause of visual impairment. Computed tomography scan images were processed using the Materialise Interactive Medical Image Control System (MIMICS) Research 21.0 software (Materialise NV, Leuven, Belgium). Eleven optic canal parameters were measured: 1) height of optic canal on the cranial side, 2) height of optic canal on the orbital side 3) length of the medial wall of the optic canal, 4) length of the lateral canal wall of the optic canal, 5) diameter of the optic canal at five points (Q1-Q4 and mid canal), and 6) area and perimeter of optic canal. These measurements were obtained for both the right and left optic canals. The study sample comprised four Crouzon syndrome, five Apert syndrome, and three Pfeiffer syndrome patients. The age of these syndromic craniosynostosis patients ranged from 2 to 63 months. The height of the optic canal on the orbital side (p = 0.041), diameter of the mid canal (p = 0.040), and diameter between the mid-canal and the cranial opening (Q3) (p = 0.079) for syndromic craniosynostosis patients were statistically narrower compared with those of normal patients when a significance level of 0.1 was considered. Scatter plots for the ages of patients versus the above parameters gave three separated clusters that suggested the arresting of optic canal development with age. The findings from this study demonstrated a narrowing of the optic canal in syndromic craniosynostosis patients, and indicate that optic canal anatomical characteristics may have an association with visual impairment among pediatric syndromic craniosynostosis patients.

Clinical study and some molecular features of Mexican patients with syndromic craniosynostosis

BACKGROUND

Craniosynostosis is one of the major genetic disorders affecting 1 in 2,100-2,500 live newborn children. Environmental and genetic factors are involved in the manifestation of this disease. The suggested genetic causes of craniosynostosis are pathogenic variants in FGFR1, FGFR2, FGFR3, and TWIST1 genes.

METHODS

In order to describe their major clinical characteristics and the presence of pathogenic variants, a sample of 36 Mexican patients with craniosynostosis diagnosed as: Crouzon (OMIM 123,500), Pfeiffer (OMIM 101,600), Apert (OMIM 101,200), Saethre-Chotzen (OMIM 101,400), and Muenke (OMIM 602,849) was analyzed.

RESULTS

In addition to craniosynostosis, most of the patients presented hypertelorism, midface hypoplasia, and abnormalities in hands and feet. To detect the pathogenic variants p.Pro252Arg FGFR1 (OMIM 136,350), p.Ser252Trp, p.Pro253Arg FGFR2 (OMIM 176,943), p.Pro250Arg, FGFR3 (OMIM 134,934), and p.Gln119Pro TWIST1 (OMIM 601,622), PCR amplification and restriction enzyme digestion were performed. Four and two patients with Apert presented the pathogenic variants p.Ser252Trp and p.Pro253Arg in FGFR2, respectively (with a frequency of 11.1% and 5.5%). The p.Pro250Arg pathogenic variant of FGFR3 was found in a patient with Muenke (with a frequency of 2.8%). The above percentages were calculated with the total number of patients.

CONCLUSION

The contribution of this work is discreet, since only 4 genes were analyzed and sample size is small. However, this strategy could be improved by sequencing the FGFR1, FGFR2, FGFR3, and TWIST1 genes, to determine different pathogenic variants. On the other hand, it would be important to include other genes, such as TCF12 (OMIM 600,480), MSX2 (OMIM 123,101), RAB23 (OMIM 606,144), and EFNB1 (OMIM 300,035), to determine their participation in craniosynostosis in the Mexican population.

Recent Advances in Craniosynostosis

Craniosynostosis is a pathologic craniofacial disorder and is defined as the premature fusion of one or more cranial (calvarial) sutures. Cranial sutures are fibrous joints consisting of nonossified mesenchymal cells that play an important role in the development of healthy craniofacial skeletons. Early fusion of these sutures results in incomplete brain development that may lead to complications of several severe medical conditions including seizures, brain damage, mental delay, complex deformities, strabismus, and visual and breathing problems. As a congenital disease, craniosynostosis has a heterogeneous origin that can be affected by genetic and epigenetic alterations, teratogens, and environmental factors and make the syndrome highly complex. To date, approximately 200 syndromes have been linked to craniosynostosis. In addition to being part of a syndrome, craniosynostosis can be nonsyndromic, formed without any additional anomalies. More than 50 nuclear genes that relate to craniosynostosis have been identified. Besides genetic factors, epigenetic factors like microRNAs and mechanical forces also play important roles in suture fusion. As craniosynostosis is a multifactorial disorder, evaluating the craniosynostosis syndrome requires and depends on all the information obtained from clinical findings, genetic analysis, epigenetic or environmental factors, or gene modulators. In this review, we will focus on embryologic and genetic studies, as well as epigenetic and environmental studies. We will discuss published studies and correlate the findings with unknown aspects of craniofacial disorders.

Signaling Mechanisms Underlying Genetic Pathophysiology of Craniosynostosis

Craniosynostosis, is the premature fusion of one or more cranial sutures which is the second most common cranial facial anomalies. The premature cranial sutures leads to deformity of skull shape and restricts the growth of brain, which might elicit severe neurologic damage. Craniosynostosis exhibit close correlations with a varieties of syndromes. During the past two decades, as the appliance of high throughput DNA sequencing techniques, steady progresses has been made in identifying gene mutations in both syndromic and nonsyndromic cases, which allow researchers to better understanding the genetic roles in the development of cranial vault. As the enrichment of known mutations involved in the pathogenic of premature sutures fusion, multiple signaling pathways have been investigated to dissect the underlying mechanisms beneath the disease. In addition to genetic etiology, environment factors, especially mechanics, have also been proposed to have vital roles during the pathophysiological of craniosynostosis. However, the influence of mechanics factors in the cranial development remains largely unknown. In this review, we present a brief overview of the updated genetic mutations and environmental factors identified in both syndromic and nonsyndromic craniosynostosis. Furthermore, potential molecular signaling pathways and its relations have been described.

Crouzon Syndrome: a Comprehensive Review

Crouzon syndrome is a rare genetic disorder with autosomal dominant inheritance. The underlying pathological process is premature synostosis of the cranial sutures with subsequent phenotypic alterations of the affected person. A review of the literature has been conducted in order to resume the overall characteristics of Crouzon syndrome such as craniomaxillofacial malformations, clinical features, dentoalveolar characteristics, aesthetic impairments, and psychological background, as well as, the different therapeutic procedures, which combine surgical and orthodontic interventions. Facial and functional malformations in individuals with Crouzon syndrome could be significantly improved after a series of surgical and orthodontic procedures in almost all cases. A multidisciplinary treatment approach would provide the best outcomes in affected patients.

Two patients with Apert syndrome with different mutations: the importance of early diagnosis

Apert syndrome is an autosomal dominant craniosynostosis syndrome accompanied by limb anomalies. The fibroblast growth factor receptor 2 (FGFR2) gene is responsible for the disease and two different heterozygous mutations, p.Pro253Arg and p.Ser252Trp, have been defined as responsible in the majority of cases of Apert syndrome. In this case report, two patients with Apert syndrome with two different FGFR2 gene mutations are presented. Case-1, a 4-month-old boy with craniosynostosis and syndactyly was referred to pediatric genetic clinic. The molecular analysis revealed p.Pro253Arg mutation in the FGFR2 gene, which confirmed the diagnosis of Apert syndrome. Case-2, a 16-year-old girl with developmental delay, cleft palate, syndactyly, and craniosynostosis, was also diagnosed as having Apert syndrome. A molecular diagnosis identified a p.Ser252Trp heterozygous mutation in the FGFR2 gene. Case-1 underwent surgery for craniosynostosis at age 10 months and he was developmentally normal during the 2 year follow-up period. As a conclusion, early surgical intervention should be considered in cases of Apert syndrome to prevent intellectual disability.

Cranial ultrasound is a reliable first step imaging in children with suspected craniosynostosis

PURPOSE

Skull radiography (SR) and Computed Tomography (CT) are still proposed as the first-line imaging choice for the diagnosis of craniosynostosis (CS) in children with abnormal head shape, but both techniques expose infants to ionizing radiation. Several studies shown that ultrasound may play an important role in the diagnosis of craniosynostosis. The aim of our study is to assess the diagnostic accuracy of cranial ultrasound scan (CUS) and confirm if it is a reliable first step imaging evaluation for the diagnosis of craniosynostosis in newborn.

METHOD

A cohort of 196 infants (122/74 males/females), with a mean age of 4 months, clinically suspected to have abnormal closure of cranial sutures, were firstly examined by CUS and then referred to neuroradiologists to perform volumetric CT scan if the suspicion of stenosis was ecographically confirmed; otherwise, a routine follow-up and physical treatment was performed, to observe the evolution of the head shape.

RESULTS

Of the 196 children studied by CUS, only two had inconclusive studies due to age limitation (>12 months). Thirty children were diagnosed with cranial synostosis at CUS and verified by CT; all the CUS results were confirmed, except two cases, that were revealed as false positives in the starting phase of the study. Twelve patients with very prominent head deformity and negative CUS underwent CT, which confirmed the CUS results in all of them; one case of closure of both temporal sutures, not studied by CUS, was documented by CT. All the 148 children with poor clinical suspicion and negative CUS underwent just a prolonged clinical follow-up. In all of them, a progressive normalization of head shape was observed, and the craniosynostosis was excluded on a clinical base.

CONCLUSIONS

CUS is a highly specific and sensitive imaging technique. In referral centers, expert hands can use it as a reliable first-step screening for infants younger than 1 year, suspected to have a craniosynostosis, thus avoiding unnecessary exposure to ionizing radiation. The "golden age" to obtain the best CUS results is under 6 months of life. Because the method is operator-dependent and there is a learning curve, a case centralization is advisable.

Understanding craniosynostosis as a growth disorder

Craniosynostosis is a condition of complex etiology that always involves the premature fusion of one or multiple cranial sutures and includes various anomalies of the soft and hard tissues of the head. Steady progress in the field has resulted in identifying gene mutations that recurrently cause craniosynostosis. There are now scores of mutations on many genes causally related to craniosynostosis syndromes, though the genetic basis for the majority of nonsyndromic cases is unknown. Identification of these genetic mutations has allowed significant progress in understanding the intrinsic properties of cranial sutures, including mechanisms responsible for normal suture patency and for pathogenesis of premature suture closure. An understanding of morphogenesis of cranial vault sutures is critical to understanding the pathophysiology of craniosynostosis conditions, but the field is now poised to recognize the repeated changes in additional skeletal and soft tissues of the head that typically accompany premature suture closure. We review the research that has brought an understanding of premature suture closure within our reach. We then enumerate the less well-studied, but equally challenging, nonsutural phenotypes of craniosynostosis conditions that are well characterized in available mouse models. We consider craniosynostosis as a complex growth disorder of multiple tissues of the developing head, whose growth is also targeted by identified mutations in ways that are poorly understood. Knowledge gained from studies of humans and mouse models for these conditions underscores the diverse, associated developmental anomalies of the head that contribute to the complex phenotypes of craniosynostosis conditions presenting novel challenges for future research. WIREs Dev Biol 2016, 5:429-459. doi: 10.1002/wdev.227 For further resources related to this article, please visit the WIREs website.

Revisiting Crouzon syndrome: reviewing the background and management of a multifaceted disease

PURPOSE

Crouzon syndrome is a complex craniosynostosis of autosomal dominant transfer, with a highly variable phenotypic appearance. Some patients are afflicted with a mild form of the disease and able to live a fully functional lifestyle, whereas many patients suffer from a severe form of the disease causing a significant impact on their quality of life. Although several case reports and genetic studies have been performed, there has been no recent review of the literature to collate the information on this disorder. In this paper, we seek to unify the findings of this disorder to provide the pediatric provider with a succinct, but complete discussion of this disease.

METHODS

Articles from 1994 to 2014 were queried on PubMed and reviewed for utility by all three researchers involved in the project. Further literature review was done on relevant articles found within references of selected articles.

RESULTS

Crouzon syndrome, although of variable penetrance, is thought to be caused in part by a mutation in the fibroblast growth factor receptor-2 (FGFR2) on chromosome 10. Aside from craniofacial malformations, the disease can also cause hearing loss and airway challenges due to malformations in the nasal cavity and nasopharyngeal airway. Management options from the perspective of the otorhinolaryngologist are diverse and revolve around craniosynostectomy, offsetting midfacial hypoplasia, addressing obstructive sleep apnea and a compromised airway, psychosocial and esthetic interventions, and ultimately requiring a multidisciplinary team approach.

CONCLUSION

Mutations in the FGFR2 are responsible for 50 % of mutations within this multifaceted syndrome. Crouzon syndrome is an autosomal dominant disorder with a number of distinguishing characteristics, including craniosynostosis, maxillary hypoplasia, exophthalmos, and multiple other features. Early intervention, both medically and surgically, as well as disciplined follow-up with the pediatric provider are crucial to the management of this disorder. In particular, management should address cranial suture release, midfacial advancement, evaluation for hearing deficits, and obstructive sleep apnea, with expedient intervention for airway compromise and increased intracranial pressure.