Craniosynostosis suggestive of Saethre-Chotzen syndrome: clinical description of a large kindred and exclusion of candidate regions on 7p

Lateral and Frontal Cephalometric Measurements in a Cohort With Saethre-Chotzen Syndrome

OBJECTIVE

Descriptions of the craniofacial morphology in Saethre-Chotzen syndrome (SCS) are primarily based on case reports or visual assessments of affected families. The aim of this study was to compare cephalometric measurements of the craniofacial skeleton in a cohort of individuals with SCS and age- and sex-matched individuals without craniofacial anomalies.

DESIGN

Retrospective case series.

PATIENTS

Eight girls and 4 boys with SCS (age range, 7.0-19.2 years).

METHODS

Cephalometric measurements were performed using lateral and frontal cephalograms.

RESULTS

Most of the individuals with Saethre-Chotzen syndrome exhibited lower values for SNA, SNB, s-n and s-ar, while their NSL/NL, NSL/ML, NL/ML, and n-s-ba values were higher than the respective mean reference values for healthy individuals. In comparison with age- and sex-matched individuals without craniofacial anomalies, the individuals with SCS showed higher values for the maxillary and mandibular angular measurements, as well as for the menton midline angle.

CONCLUSIONS

This sample of 12 unrelated individuals with SCS is the largest collected to date for cephalometric measurements. We found that the syndrome is associated with bimaxillary retrognathism, posterior maxillary and mandibular inclination, neutral sagittal relation as well as a tendency toward an open vertical skeletal relation, a short and flattened skull base, and facial asymmetry, as compared to individuals without the syndrome.

Modeling congenital disease and inborn errors of development in Drosophila melanogaster

Fly models that faithfully recapitulate various aspects of human disease and human health-related biology are being used for research into disease diagnosis and prevention. Established and new genetic strategies in Drosophila have yielded numerous substantial successes in modeling congenital disorders or inborn errors of human development, as well as neurodegenerative disease and cancer. Moreover, although our ability to generate sequence datasets continues to outpace our ability to analyze these datasets, the development of high-throughput analysis platforms in Drosophila has provided access through the bottleneck in the identification of disease gene candidates. In this Review, we describe both the traditional and newer methods that are facilitating the incorporation of Drosophila into the human disease discovery process, with a focus on the models that have enhanced our understanding of human developmental disorders and congenital disease. Enviable features of the Drosophila experimental system, which make it particularly useful in facilitating the much anticipated move from genotype to phenotype (understanding and predicting phenotypes directly from the primary DNA sequence), include its genetic tractability, the low cost for high-throughput discovery, and a genome and underlying biology that are highly evolutionarily conserved. In embracing the fly in the human disease-gene discovery process, we can expect to speed up and reduce the cost of this process, allowing experimental scales that are not feasible and/or would be too costly in higher eukaryotes.

Additional phenotypic features of Muenke syndrome in 2 Dutch families

In about 30% of the patients with syndromal craniosynostosis, a genetic mutation can be traced. For the purpose of adequate genetic counseling and treatment of these patients, the full spectrum of clinical findings for each specific mutation needs to be appreciated. The Pro250Arg mutation in the FGFR3 gene is found in patients with Muenke syndrome and is one of the most frequently encountered mutations in craniosynostosis syndromes. A number of studies on the relationship between genotype and phenotype concerning this specific mutation have been published. Two Dutch families with Muenke syndrome were screened for the reported characteristics of this syndrome and for additional features. New phenotypical findings were hypoplasia of the frontal sinus, ptosis of the upper eyelids, dysplastic elbow joints with restricted elbow motion, and mild cutaneous syndactyly. Incidentally, polydactyly, severe ankylosis of the elbow, fusion of cervical vertebrae, and epilepsy were found. Upper eyelid ptosis is thought to be pathognomonic for Saethre-Chotzen syndrome but was also observed in our series of patients with Muenke syndrome. Because Muenke and Saethre-Chotzen syndrome can have similar phenotypes, DNA analysis is needed to distinguish between these syndromes, even when a syndrome diagnosis is already made in a family member.

Deletion of the TWIST gene in a large five-generation family

In this article, we describe a large five-generation family with characteristics of the Saethre-Chotzen syndrome as well as of the blepharophimosis ptosis epicanthus inversus syndrome. Segregating with their phenotype is a deletion of the chromosome 7p21 TWIST gene locus. The TWIST gene indeed is involved in Saethre-Chotzen syndrome, a craniosynostosis syndrome further characterized by specific facial and limb abnormalities. However, only two members of our family exhibited craniosynostosis. This report demonstrates that the genetics of craniofacial anomalies are less straightforward than they sometimes appear to be. Not only craniosynostosis, but also subtle facial deformities could be indicative of an abnormality of the TWIST gene. In conclusion, the clinical spectrum of genetic abnormalities of the TWIST gene is highly variable. We therefore recommend that genetic analysis of the TWIST gene locus, including fluorescence in situ hybridization, should be considered in familial cases of facial and eyelid abnormalities without the presence of craniosynostosis.

Genetic heterogeneity of Saethre-Chotzen syndrome, due to TWIST and FGFR mutations

Thirty-two unrelated patients with features of Saethre-Chotzen syndrome, a common autosomal dominant condition of craniosynostosis and limb anomalies, were screened for mutations in TWIST, FGFR2, and FGFR3. Nine novel and three recurrent TWIST mutations were found in 12 families. Seven families were found to have the FGFR3 P250R mutation, and one individual was found to have an FGFR2 VV269-270 deletion. 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. More than 35 different TWIST mutations are now known in the literature. The most common phenotypic features, present in more than a third of our patients with TWIST mutations, are coronal synostosis, brachycephaly, low frontal hairline, facial asymmetry, ptosis, hypertelorism, broad great toes, and clinodactyly. Significant intra- and interfamilial phenotypic variability is present for either TWIST mutations or FGFR mutations. The overlap in clinical features and the presence, in the same genes, of mutations for more than one craniosynostotic condition-such as Saethre-Chotzen, Crouzon, and Pfeiffer syndromes-support the hypothesis that TWIST and FGFRs are components of the same molecular pathway involved in the modulation of craniofacial and limb development in humans.

Syndrome of coronal craniosynostosis with brachydactyly and carpal/tarsal coalition due to Pro250Arg mutation in FGFR3 gene

Recently, a unique Pro250Arg point mutation in fibroblast growth factor receptor 3 (FGFR3) was reported in 61 individuals with coronal craniosynostosis from 20 unrelated families [Muenke et al. (1997): Am J Hum Genet 60:555-564]. The discovery of this apparently common mutation has resulted in the definition of a recognizable syndrome, through analysis of subtle clinical findings in families who were previously thought to have a variety of other craniosynostosis syndromes. Previous diagnoses in some of these families have included Jackson-Weiss, Saethre-Chotzen, and Pfeiffer syndromes, as well as Adelaide-type craniosynostosis and brachydactyly-craniosynostosis syndrome [Adès et al. (1994): Am J Med Genet 51:121-130; von Gernet et al. (1996): Am J Med Genet 63:177-184; Reardon et al. (1997): J Med Genet 34:632-636; Bellus et al. (1996): Nat Genet 14:174-176; Hollaway et al. (1995): Hum Mol Genet 4:681-683; Glass et al. (1994): Clin Dysmorphol 3:215-223]. There appears to be a need to further delineate the phenotype associated with this common mutation in FGFR3. We compare the clinical characteristics of previously reported cases of this unique Pro250Arg mutation with those of two additional families and suggest that this syndrome with a unique mutational basis be designated coronal craniosynostosis with brachydactyly and carpal/tarsal coalition due to Pro250Arg mutation in FGFR3 gene, to emphasize the distinctive findings which may be present even in the absence of coronal craniosynostosis.

Phenotypic expression of the fibroblast growth factor receptor 3 (FGFR3) mutation P250R in a large craniosynostosis family

The craniosynostosis syndromes are a heterogeneous group of sporadic, autosomal dominant disorders with significant clinical overlap. Recently, we described a large family with autosomal dominant craniosynostosis suggestive of Saethre-Chotzen syndrome, in which linkage to the Saethre-Chotzen syndrome loci on 7p had been excluded. We now report the presence of a mutation in the fibroblast growth factor receptor 3 (FGFR3) in this family. The mutation, P250R, had been previously reported in 10 patients with non-syndromic craniosynostosis. Variable expression of this mutation is evident especially in two additional members of this family, one of whom is severely affected with pancraniosynostosis. The family provides a further example of genetic heterogeneity and variable expression of the craniosynostosis syndromes and broadens the phenotypic spectrum associated with the FGFR3 mutation P250R. In addition, we found a polymorphism (F384L) in the transmembrane domain of FGFR3 which occurs with a frequency of 3% in the Turkish population but is uncommon among Germans.

Prevalence of Pro250Arg mutation of fibroblast growth factor receptor 3 in coronal craniosynostosis

BACKGROUND

The C749G (Pro250Arg) mutation in the gene for fibroblast growth factor receptor 3 (FGFR3) has been found in patients with various types of craniosynostosis. We aimed to find out the proportion of cases of apparently non-syndromic coronal craniosynostosis attributable to this mutation.

METHODS

We studied 26 patients with coronal craniosynostosis but no syndromic diagnosis, who were referred to a supra-regional specialist centre. Genomic DNA was analysed by PCR and restriction-enzyme digestion to identify the C749G mutation in FGFR3. Family members of patients found to have the mutation were also tested.

FINDINGS

Eight (31%) of the 26 probands were heterozygous for the C749G mutation. In two cases, the mutation showed autosomal dominant transmission with evidence of variable expressivity; the remaining six cases were sporadic. We demonstrated in six families that the mutation had arisen de novo from clinically unaffected parents.

INTERPRETATION

The C749G mutation in FGFR3 is a frequent cause of apparently non-syndromic coronal craniosynostosis. Our finding will aid genetic counselling and prenatal diagnosis. The mutation rate at this nucleotide is one of the highest described in the human genome.

Mutations in TWIST, a basic helix-loop-helix transcription factor, in Saethre-Chotzen syndrome

Saethre-Chotzen syndrome is one of the most common autosomal dominant disorders of craniosynostosis in humans and is characterized by craniofacial and limb anomalies. The locus for Saethre-Chotzen syndrome maps to chromosome 7p21-p22. We have evaluated TWIST, a basic helix-loop-helix transcription factor, as a candidate gene for this condition because its expression pattern and mutant phenotypes in Drosophila and mouse are consistent with the Saethre-Chotzen phenotype. We mapped TWIST to human chromosome 7p21-p22 and mutational analysis reveals nonsense, missense, insertion and deletion mutations in patients. These mutations occur within the basic DNA binding, helix I and loop domains, or result in premature termination of the protein. Studies in Drosophila indicate that twist may affect the transcription of fibroblast growth factor receptors (FGFRs), another gene family implicated in human craniosynostosis. The emerging cascade of molecular components involved in craniofacial and limb development now includes TWIST, which may function as an upstream regulator of FGFRs.

Identical mutations in three different fibroblast growth factor receptor genes in autosomal dominant craniosynostosis syndromes

Pfeiffer syndrome (PS; McKusick MIM 101,600) is an autosomal dominant craniosynostosis syndrome with characteristic craniofacial anomalies and broad thumbs and big toes. We have previously demonstrated genetic heterogeneity in PS and mapped a gene to chromosome 8 (ref. 3) and a second to chromosome 10 (ref. 4). The gene on chromosome 8 is the fibroblast growth factor receptor 1 (FGFR1) with a common mutation (C755G) predicting a Pro252Arg substitution. The gene on chromosome 10 is FGFR2 with several different mutations causing sporadic and familial PS (Table 1). We report a recurrent single point mutation in the FGFR3 gene, located on chromosome 4p, in ten unrelated families with craniosynostosis syndromes. This mutation (C749G) predicts a Pro250Arg amino acid substitution in the extracellular domain of the FGFR3 protein. Interestingly, this common mutation occurs precisely at the analogous position within the FGFR3 protein as the mutations in FGFR1 (Pro252Arg) and FGFR2 (Pro253Arg) previously reported in Pfeiffer and Apert syndromes, respectively.