The mapping of a gene for craniosynostosis: evidence for linkage of the Saethre-Chotzen syndrome to distal chromosome 7p

Genetic Heterogeneity, Craniofacial Surgical Burden, and Surgical Techniques in Patients With Saethre-Chotzen Syndrome

OBJECTIVE

While genotype correlates with phenotype in patients with many forms of syndromic craniosynostosis, the relationship between molecular diagnosis and craniofacial surgical history in patients with Saethre-Chotzen syndrome (SCS) is more variable. This manuscript characterizes that relationship and evaluates operative trends in these patients over the past 3 decades.

METHODS

Demographic information, molecular diagnosis, and craniofacial surgical history in patients born with SCS between 1989 and 2023 were compared with appropriate statistics, including t tests and analysis of variance.

RESULTS

Thirty-five patients with SCS were included, and there was no difference in total craniofacial procedures among those with TWIST1 substitutions (2.1 ± 1.6), duplications (3.0 ± 4.2), insertions (3.5 ± 0.7), or deletions (2.4 ± 1.9; P = 0.97). Cranial expansion rates were also similar across all genetic diagnoses (P>0.05), and surgical incidence was similar across patients with unicoronal, bicoronal, and multisuture involvement (P > 0.05). Those with an initial fronto-orbital advancement had a lower incidence of secondary cranial vault procedures compared with those with an initial posterior vault distraction osteogenesis (29% versus 71%, P < 0.05), though this did not control for phenotypic severity. On average, total cranial vault surgical burden (1.35 ± 0.67 versus 1.75 ± 0.46) and cranial expansion surgical burden (1.40 ± 0.68 versus 1.88 ± 0.64) between the fronto-orbital advancement-first and posterior vault distraction osteogenesis-first cohorts were similar (P = 0.11, P = 0.17, respectively).

CONCLUSION

While SCS is molecularly and phenotypically heterogeneous, genetic diagnosis does not appear associated with rates of craniofacial surgery. Additional prospective study of correlations between genotype, severity of craniofacial manifestations, and treatment algorithms is warranted; but, in the end, it may be that this highly variable form of syndromic craniosynostosis warrants tailored, expectant management.

Patient Tailored Surgery in Saethre-Chotzen Syndrome: Analysis of Reoperation for Intracranial Hypertension

Saethre-Chotzen syndrome (SCS) is a syndromic craniosynostosis with pathogenic variants in the TWIST1 gene showing a broad phenotypic spectrum. Controversies exist in the literature regarding surgical management with single one-stage versus patient-tailored surgery and the related reoperation rate for intracranial hypertension of up to 42%. At our center, SCS patients are offered patient-tailored surgery with single-stage fronto-orbital advancement and remodeling or fronto-orbital advancement and remodeling and posterior distraction in an individually determined order. The authors' database identified 35 confirmed SCS patients between 1999 and 2022. Involved sutures in craniosynostosis were left unicoronal (22.9%), bicoronal (22.9%), sagittal (8.6%), bicoronal and sagittal (5.7%), right unicoronal (2.9%), bicoronal and metopic (2.9%), bicoronal, sagittal and metopic (2.9%), and bilateral lambdoid (2.9%). There was pansynostosis in 8.6% and no craniosynostosis in 14.3% of the patients. Twenty-six patients, 10 females, and 16 males were operated on. Mean age at the first surgery was 1.70 years, and 3.86 years at the second surgery. Eleven of 26 patients had invasive intracranial pressure monitoring. Three patients presented with papilledema before the first surgery and 4 afterward. Four of the 26 operated patients were operated initially elsewhere. The other 22 patients were initially referred to our unit and underwent patient-tailored surgery. Nine of these patients (41%) had a second surgery, and 3 (14%) of them were because of raised intracranial pressure. Seven (27%) of all operated patients had a complication. Median follow-up was 13.98 years (range, 1.85-18.08). Patient-tailored surgery in a specialized center and long-term follow-up allow for a low reoperation rate for intracranial hypertension.

Saethre-Chotzen syndrome: long-term outcome of a syndrome-specific management protocol

AIM

To assess the long-term outcomes of our management protocol for Saethre-Chotzen syndrome, which includes one-stage fronto-orbital advancement.

METHOD

All patients born with Saethre-Chotzen syndrome between January 1992 and March 2017 were included. Evaluated parameters included occipital frontal head circumference (OFC), fundoscopy, neuroimaging (ventricular size, tonsillar position, and the presence of collaterals/an abnormal transverse sinus), polysomnography, and ophthalmological outcomes. The relationship between papilledema and its associated risk factors was evaluated with Fisher's exact test.

RESULTS

Thirty-two patients (21 females, 11 males) were included. Median (SD) age at first surgery was 9.6 months (3.1mo) for patients who were primarily referred to our center (range: 3.6-13.0mo), the median (SD) age at last follow-up was 13 years (5y 7mo; range: 3-25y). Seven patients had papilledema preoperatively, which recurred in two. Two patients had papilledema solely after first surgery. Second cranial vault expansion was indicated in 20%. Thirteen patients had an OFC deflection, indicating restricted skull growth, one patient had ventriculomegaly, and none developed hydrocephalus. Eleven patients had emissary veins, while the transverse sinus was aberrant unilaterally in 13 (hypoplastic n=10 and absent n=3). Four patients had mild tonsillar descent, one of which was a Chiari type I malformation. Four patients had obstructive sleep apnoea (two mild, one moderate, and one severe). An aberrant transverse sinus was associated with papilledema (p=0.01).

INTERPRETATION

Single one-stage fronto-orbital advancement was sufficient to prevent intracranial hypertension for 80% of our patients with Saethre-Chotzen syndrome. Follow-up should focus on OFC deflection and venous anomalies.

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.

Structural Genome Variations Related to Craniosynostosis

Craniosynostosis refers to a condition during early development in which one or more of the fibrous sutures of the skull prematurely fuse by turning into bone, which produces recognizable patterns of cranial shape malformations depending on which suture(s) are affected. In addition to cases with isolated cranial dysmorphologies, craniosynostosis appears in syndromes that include skeletal features of the eyes, nose, palate, hands, and feet as well as impairment of vision, hearing, and intellectual development. Approximately 85% of the cases are nonsyndromic sporadic and emerge after de novo structural genome rearrangements or single nucleotide variation, while the remainders consist of syndromic cases following mendelian inheritance. By karyotyping, genome wide linkage, and CNV analyses as well as by whole exome and whole genome sequencing, numerous candidate genes for craniosynostosis belonging to the FGF, Wnt, BMP, Ras/ERK, ephrin, hedgehog, STAT, and retinoic acid signaling pathways have been identified. Many of the craniosynostosis-related candidate genes form a functional network based upon protein-protein or protein-DNA interactions. Depending on which node of this craniosynostosis-related network is affected by a gene mutation or a change in gene expression pattern, a distinct craniosynostosis syndrome or set of phenotypes ensues. Structural variations may alter the dosage of one or several genes or disrupt the genomic architecture of genes and their regulatory elements within topologically associated chromatin domains. These may exert dominant effects by either haploinsufficiency, dominant negative partial loss of function, gain of function, epistatic interaction, or alteration of levels and patterns of gene expression during development. Molecular mechanisms of dominant modes of action of these mutations may include loss of one or several binding sites for cognate protein partners or transcription factor binding sequences. Such losses affect interactions within functional networks governing development and consequently result in phenotypes such as craniosynostosis. Many of the novel variants identified by genome wide CNV analyses, whole exome and whole genome sequencing are incorporated in recently developed diagnostic algorithms for craniosynostosis.

A novel de novo deletion of chromosome 7 [46,XX,del(7)(p14.2 p15.1)] in a child with feeding problems

The phenotype and severity of symptoms associated with deletions on chromosome 7 are directly proportional to the size of the deleted segment. Distal and interstitial deletions have been described in 40 cases. In this report the authors aim to report a child with a novel de novo interstitial deletion on chromosome 7, with the following karyotype: 46,XX,del(7)(p14.2 p15.1). We described a female, born at 38 weeks with intrauterine growth restriction and feeding problems with episodes of cyanosis after feedings and failure to thrive. Physical examination showed low implantation of ears, hypertelorism, oblique palpebral fissures, retrognathia, and palate ogived, with insertion anomalies of the toes, poor facial expression and mild axial hypotonia. Transfontanelar ultrasound, magnetic resonance imaging, bronchofibroscopy and metabolic studies were normal. She was hospitalized until the 32nd day of life. She started speech therapy and presented improvements in swallowing. The percutaneous endoscopic gastrostomy was removed at 36 months. She had recurrent urinary tract infection with normal dimercaptosuccinic acid but with a vesicoureteral reflux (grade III). Imagiological studies revealed a bilateral osteonecrosis of femoral epiphysis (Legg-Calvé-Perthes disease). Currently (6years-old), she is being normally fed (body mass index=15.8kg/m(2)). Her weight is 16.4kg (3rd centile) and length is 105cm (3rd to 5th centiles). She has a mild delay of psychomotor development impairment and some speech problems. This is the first case report of a patient with this de novo small interstitial deletion on chromosome 7. This rare chromosomal abnormality was associated with severe feeding problems in the first years of life.

Molecular signaling in pathogenesis of craniosynostosis: the role of fibroblast growth factor and transforming growth factor–β

The interplay of signals between dura mater, suture mesenchyme, and brain is essential in determining the fate of cranial sutures and the pathogenesis of premature suture fusion leading to craniosynostosis. At the forefront of research into suture fusion is the role of fibroblast growth factor and transforming growth factor–β, which have been found to be critical in the cell-signaling cascade involved in aberrant suture fusion. In this review, the authors discuss recent and ongoing research into the role of fibroblast growth factor and transforming growth factor–β in the etiopathogenesis of craniosynostosis.

Why do we behave as we do?

It is important for surgeons to have insight into themselves, their life stories, and the rationales they use to convince themselves that their actions are unselfish and well motivated. The battle between Philanthropia and Philotechnica was recognized by Hippocrates and is still a source of internal strife for many surgeons: the need to perform an operation that they are poorly equipped to do offset against the knowledge that it could be better done by someone else. In the treatment or referral for treatment of children with craniosynostosis and craniofacial syndromes, appropriate referrals are often not made or are made only after some problem has occurred as a result of surgical intervention. Several instances of children receiving extensive surgery for wrongly diagnosed craniosynostosis are explored. The thesis is that only by knowing our own internal motivations can we avoid falling into a posture that is good for our own egos and pocketbooks but bad for our patients.

Ocular phenotype correlations in patients with TWIST versus FGFR3 genetic mutations

BACKGROUND/PURPOSE

Despite the similar clinical phenotype of the Saethre-Chotzen and Muenke craniosynostoses, the 2 syndromes are now genotypically distinct. Patients with Saethre-Chotzen and Muenke syndromes carry mutations in the TWIST and fibroblast growth factor receptor (FGFR) 3 genes, respectively. We sought to assess possible ocular phenotypic differences in patients with mutations of either gene previously grouped according to phenotype only.

METHODS

A retrospective chart review was performed for 21 children with known mutations of the TWIST (n=10) or the FGFR3 (n=11) genes. Data gathered included patient sex, age, family craniofacial history, craniofacial and ophthalmic surgeries, type of strabismus, ptosis, cycloplegic refraction, visual acuity, the presence of amblyopia, nasolacrimal duct obstruction (NLDO), nystagmus, hypertelorism, epicanthal fold anomalies, and any ocular structural abnormalities.

RESULTS

In the TWIST group, ptosis was present in 90%, amblyopia in 70%, horizontal strabismus in 70%, vertical strabismus in 60%, NLDO in 60%, astigmatism in 50%, inferior oblique overaction (IOOA) in 40%, hyperopia in 40%, myopia in 30%, nystagmus in 30%, and optic nerve findings in 30%. In the FGFR3 group, ptosis was present in 36%, amblyopia in 18%, horizontal strabismus in 55%, vertical strabismus in 36%, NLDO in 0%, astigmatism in 9%, IOOA in 45%, hyperopia in 27%, myopia in 18%, nystagmus in 18%, and optic nerve findings in 27%.

CONCLUSIONS

Patients with TWIST gene mutations may have more ophthalmic abnormalities, including more strabismus, ptosis, NLDO, astigmatism, vertical deviations, and amblyopia compared with patients with FGFR3 gene mutations.

The polymerase chain reaction and its application to clinical plastic surgery

Molecular biology has become an essential component in many fields of modern medical research, including plastic surgery. Research into the molecular mechanisms underlying many disease processes offer increased understanding of the pathogenesis of disease and provide exciting therapeutic possibilities. Yet for many clinicians, the presentation of much research into molecular biological processes is couched in confusing terminology and based on scientific techniques, the basis of which are frequently difficult for the clinician to understand. The purpose of this review is to present an introduction to some of the molecular biological techniques currently in use, namely the polymerase chain reaction (PCR) and explore its applications to different aspects of plastic surgery. This review explores the role PCR now plays in all aspects of modern plastic surgery practise, with particular emphasis on normal and abnormal wound healing, the diagnosis of craniofacial anomalies, the diagnosis and treatment of cancer including melanoma and squamous cell carcinoma of the head and neck, and burns.

Trigonocephaly in Muenke syndrome

Saethre-Chotzen syndrome is caused by mutations in the TWIST gene on chromosome 7p21.2. However, Muenke et al. [(1997); Am J Hum Genet 91: 555-564] described a new subgroup carrying the Pro250Arg mutation in the fibroblast growth factor receptor (FGFR) 3 gene on chromosome 4p16. Uni or bicoronal synostosis appears to be the main clinical finding in both syndromes. We observed trigonocephaly as a new manifestation in Muenke syndrome. As a consequence we advise to routinely perform mutation analysis of the FGFR1, 2, and 3 genes in children with non-syndromic trigonocephaly.

Clinical and Genetic Analysis of Patients with Saethre-Chotzen Syndrome

BACKGROUND

Saethre-Chotzen syndrome is a craniosynostosis syndrome further characterized by distinctive facial and limb abnormalities. It shows complete penetrance and variable expressivity and has been linked to the TWIST gene on chromosome 7p21; more than 80 different intragenic mutations and, recently, large deletions have been detected in Saethre-Chotzen patients. The aim of this study was to genetically and phenotypically characterize patients with a clinical diagnosis of Saethre-Chotzen syndrome.

METHODS

Patients with a clinical diagnosis as well as those with a genetic diagnosis of Saethre-Chotzen syndrome (n = 34) were included in the study.

RESULTS

The study showed that the important features of Saethre-Chotzen syndrome are brachycephaly (occurring in 74 percent of patients), a broad, depressed nasal bridge (65 percent), a high forehead (56 percent), ptosis (53 percent), and prominent auricular crura (56 percent). Furthermore, using different molecular techniques, pathogenic mutations in the TWIST gene were identified in 71 percent of patients.

CONCLUSIONS

Patients with deletions of the TWIST gene did not differ from those with intragenic TWIST mutations in frequency or severity of craniofacial abnormalities. However, they did distinguish themselves by the presence of many additional anomalies and diseases and--most importantly--the high frequency of mental retardation, which was borderline significant. 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.

A diagnostic approach to identifying submicroscopic 7p21 deletions in Saethre-Chotzen syndrome: fluorescence in situ hybridization and dosage-sensitive Southern blot analysis

PURPOSE

To report on the use of fluorescence in situ hybridization (FISH) and dosage-sensitive Southern blot analysis in the molecular diagnosis of patients with Saethre-Chotzen syndrome.

METHODS

FISH and dosage-sensitive Southern blot analysis utilizing TWIST gene probes were performed on patients with Saethre-Chotzen syndrome but without an identifiable TWIST sequence variation.

RESULTS

Four unrelated patients with a deletion of the TWIST gene were identified by Southern blot; one of them had a complex chromosomal rearrangement involving 7p21 and no apparent deletion by FISH, suggesting a smaller deletion in the region including the TWIST gene. A fifth patient had an abnormal TWIST gene fragment on Southern blot analysis that segregated with the disease in the family; FISH was normal in this patient, suggesting a partial deletion or rearrangement in or near the gene.

CONCLUSION

FISH and dosage-sensitive Southern blot analysis are useful diagnostic tools in Saethre-Chotzen syndrome without TWIST sequence variation.

Mutations in the human TWIST gene

Saethre-Chotzen syndrome is a relatively common craniosynostosis disorder with autosomal dominant inheritance. Mutations in the TWIST gene have been identified in patients with Saethre-Chotzen syndrome. The TWIST gene product is a transcription factor with DNA binding and helix-loop-helix domains. Numerous missense and nonsense mutations cluster in the functional domains, without any apparent mutational hot spot. Two novel point mutations and one novel polymorphism are included in this review. Large deletions including the TWIST gene have been identified in some patients with learning disabilities or mental retardation, which are not typically part of the Saethre-Chotzen syndrome. Comprehensive studies in patients with the clinical diagnosis of Saethre-Chotzen syndrome have demonstrated a TWIST gene abnormality in about 80%, up to 37% of which may be large deletions [Johnson et al., 1998]. The gene deletions and numerous nonsense mutations are suggestive of haploinsufficiency as the disease-causing mechanism. No genotype phenotype correlation was apparent.

A comprehensive screen for TWIST mutations in patients with craniosynostosis identifies a new microdeletion syndrome of chromosome band 7p21.1

Mutations in the coding region of the TWIST gene (encoding a basic helix-loop-helix transcription factor) have been identified in some cases of Saethre-Chotzen syndrome. Haploinsufficiency appears to be the pathogenic mechanism involved. To investigate the possibility that complete deletions of the TWIST gene also contribute to this disorder, we have developed a comprehensive strategy to screen for coding-region mutations and for complete gene deletions. Heterozygous TWIST mutations were identified in 8 of 10 patients with Saethre-Chotzen syndrome and in 2 of 43 craniosynostosis patients with no clear diagnosis. In addition to six coding-region mutations, our strategy revealed four complete TWIST deletions, only one of which associated with a translocation was suspected on the basis of conventional cytogenetic analysis. This case and two interstitial deletions were detectable by analysis of polymorphic microsatellite loci, including a novel (CA)n locus 7.9 kb away from TWIST, combined with FISH; these deletions ranged in size from 3.5 Mb to >11.6 Mb. The remaining, much smaller deletion was detected by Southern blot analysis and removed 2,924 bp, with a 2-bp orphan sequence at the breakpoint. Significant learning difficulties were present in the three patients with megabase-sized deletions, which suggests that haploinsufficiency of genes neighboring TWIST contributes to developmental delay. Our results identify a new microdeletion disorder that maps to chromosome band 7p21.1 and that causes a significant proportion of Saethre-Chotzen syndrome.

[Anesthesia and intensive care of craniostenosis and craniofacial dysmorphism in children]

Craniosynostosis occurs in one out of 2,000 births. It results in primary skull deformations requiring surgical repair, in infants with a body weight of less than 10 kg. Pure craniosynostosis is the most frequent situation, where the risk for cerebral compression during brain development is the lowest. Therefore the aim of surgical correction in this case is mainly cosmetic. Conversely, in syndromic craniosynostosis, associated malformations are more common and cerebral, visual and respiratory consequences of complex facio-craniosynostosis are usually severe. Current surgical techniques consist of a total skull vault reconstruction which carry a high risk of sudden and major blood losses. Intraoperatively, whatever the type of craniosynostosis, mean blood losses corresponding to 90% of estimated red cell mass have to be anticipated. These blood losses vary according to the type of skull deformation and the type of surgery. Accurate evaluation is usually difficult and must be based more on calculation of red cell mass variations than on simple monitoring of surgical drainage. Invasive haemodynamic monitoring is always required. To reduce the amount of homologous blood transfusion, peroperative haemodilution seems to be the most suitable technique, due to unresolved technical difficulties in autotransfusion practice in infants. Severe facial deformities are associated with chronic hypoxaemia and cerebral compression representing major risk for these children in poor condition undergoing such major surgical procedures. With experienced teams, this high-risk surgery carries a low peroperative mortality (less than 1%) and morbidity rate. The latter includes essentially transient peroperative hypotension. The excellent final cosmetic and functional results justify the practice of this surgery in children with a bodyweight of less than 10 kg.

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.

Craniofacial developmental abnormalities

Major advances have been made in the elucidation of the molecular basis of a number of human dysmorphic syndromes involving abnormalities of craniofacial development. This will lead, in turn, to a greater understanding of the mechanisms that underlie normal craniofacial development.

Craniosynostosis associated with FGFR3 pro250arg mutation results in a range of clinical presentations including unisutural sporadic craniosynostosis

Several mutations involving the fibroblast growth factor receptor (FGFR) gene family have been identified in association with phenotypically distinct forms of craniosynostosis. One such point mutation, resulting in the substitution of proline by arginine in a critical region of the linker region between the first and second immunoglobulin-like domains, is associated with highly specific phenotypic consequences in that mutation at this point in FGFR1 results in Pfeiffer syndrome and analogous mutation in FGFR2 results in Apert syndrome. We now show that a much more variable clinical presentation accompanies analogous mutation in the FGFR3 gene. Specifically, mental retardation, apparently unrelated to the management of the craniosynostosis, appears to be a variable clinical consequence of this FGFR3 mutation.

A unique point mutation in the fibroblast growth factor receptor 3 gene (FGFR3) defines a new craniosynostosis syndrome

The underlying basis of many forms of syndromic craniosynostosis has been defined on a molecular level. However, many patients with familial or sporadic craniosynostosis do not have the classical findings of those craniosynostosis syndromes. Here we present 61 individuals from 20 unrelated families where coronal synostosis is due to an amino acid substitution (Pro250Arg) that results from a single point mutation in the fibroblast growth factor receptor 3 gene on chromosome 4p. In this instance, a new clinical syndrome is being defined on the basis of the molecular finding. In addition to the skull findings, some patients had abnormalities on radiographs of hands and feet, including thimble-like middle phalanges, coned epiphyses, and carpal and tarsal fusions. Brachydactyly was seen in some cases; none had clinically significant syndactyly or deviation of the great toe. Sensorineural hearing loss was present in some, and developmental delay was seen in a minority. While the radiological findings of hands and feet can be very helpful in diagnosing this syndrome, it is not in all cases clearly distinguishable on a clinical basis from other craniosynostosis syndromes. Therefore, this mutation should be tested for in patients with coronal synostosis.

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.

Mutations of the TWIST gene in the Saethre-Chotzen syndrome

Saethre-Chotzen syndrome (acrocephalo-syndactyly type III, ACS III) is an autosomal dominant craniosynostosis with brachydactyly, soft tissue syndactyly and facial dysmorphism including ptosis, facial asymmetry and prominent ear crura. ACS III has been mapped to chromosome 7p21-22. Of interest, TWIST, the human counterpart of the murine Twist gene, has been localized on chromosome 7p21 as well. The Twist gene product is a transcription factor containing a basic helix-loop-helix (b-HLH) domain, required in head mesenchyme for cranial neural tube morphogenesis in mice. 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. Here, we report 21-bp insertions and nonsense mutations of the TWIST gene (S127X, E130X) in seven ACS III probands and describe impairment of head mesenchyme induction by TWIST as a novel pathophysiological mechanism in human craniosynostoses.

Saethre-Chotzen syndrome: a clinical, EEG and neuroradiological study

Saethre-Chotzen syndrome is a form of acrocephalosyndactyly with autosomal dominant inheritance, characterized by craniosynostosis, facial asymmetry, palpebral ptosis, deviated nasal septum, partial cutaneous syndactyly, and various skeletal abnormalities. We studied in detail the neurological, EEG, and neuroradiological features of a group of 11 (6 male, 5 female) patients with Saethre-Chotzen syndrome. Four subjects were affected by seizures; they had paroxysmal EEG abnormalities, and gross neuroimaging revealed destructive brain lesions or malformations. Our findings suggest that CNS involvement in Saethre-Chotzen syndrome might be more severe than previously reported and support the wider use of neurophysiological and neuroimaging techniques in the study of children with this syndrome.

Localization of a novel t(1;7) translocation associated with Wilms' tumor predisposition and skeletal abnormalities

Cytogenetic analysis of predisposition syndromes has played a critical role in the elucidation of the genetics of Wilms' tumor (WT). Therefore, we became interested in a patient who presented with a WT and a nephrogenic rest in the contralateral kidney (suggestive of a predisposition) and a de novo t(1;7)(q42;p15) constitutional translocation as the only visible cytogenetic abnormality. He also had bilateral radial aplasia and other skeletal abnormalities, but there was no manifestation of any syndrome previously associated with WT. In the tumor, the translocation was retained, and the other 7p region was lost by the formation of an isochromosome i(7q). Here, we report the localization of the chromosome 7 breakpoint within a yeast artificial chromosome (YAC) contig by using fluorescence in situ hybridization (FISH), localizing the breakpoint between markers sWSS355 and sWSS1449. A number of YACs span the breakpoint and, thus, contain the region that is disrupted by the translocation. This may represent the site of a novel tumor suppressor gene that is involved in WT and also in normal renal development.

Hearing loss in the Saethre-Chotzen syndrome

A three-generation family with Saethre-Chotzen syndrome and an isolated case are presented. The proband presented with conductive hearing loss. His mother and grandmother showed minor features of the syndrome including conductive hearing loss. Symptoms of the craniosynostosis syndromes can include stapes ankylosis, a fixed ossicular chain in a too small epitympanum, and small or even absent mastoids. The proband was treated with a bone-anchored hearing aid (BAHA) instead of reconstructive middle ear surgery. Current literature on the results of ear surgery is reviewed. In general, reconstructive middle ear surgery should be considered if congenital anomalies of the middle ear are the only presenting symptom. In cases with additional anomalies such as atresia of the ear canal or damage due to chronic ear infections, the outcome of reconstructive surgery to correct the anomalous ossicular chain is unsatisfactory. In such cases of the BAHA is probably the best solution.

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

We describe the clinical manifestations of an autosomal dominant form of craniosynostosis in a large family with eight affected relatives. Unilateral or bilateral coronal synostosis, low frontal hair line, strabismus, ptosis, and partial cutaneous syndactyly of fingers and toes are findings suggestive of the diagnosis of Saethre-Chotzen syndrome. The disease locus was excluded from the two adjacent Saethre-Chotzen candidate regions on 7p by linkage analysis with markers D7S664 and D7S507. This indicates heterogeneity of Saethre-Chotzen syndrome with a locus outside the candidate regions on 7p.

Craniosynostosis, Philadelphia type: a new autosomal dominant syndrome with sagittal craniosynostosis and syndactyly of the fingers and toes

The acrocephalosyndactyly syndromes (ACS) are a group of clinically similar disorders that share the manifestations of craniosynostosis and a variety of hand and foot anomalies. Here we report on a 5-generation kindred segregating sagittal craniosynostosis and syndactyly of the fingers and the toes in an autosomal dominant manner. The anomalies seen in this kindred comprise a syndrome distinct from other craniosynostosis syndromes. For this novel syndrome, we propose the name craniosynostosis, Philadelphia type.

The molecular pathology of syndromic craniosynostosis

Several monogenic disorders result in craniosynostosis, the premature fusion of skull sutures in the neonate, causing craniofacial malformation and, occasionally, neurological compromise. These malformations were initially classified on a clinical basis, but several recent reports have clarified the underlying mutations in many of these syndromes, allowing the complexity of the relationship between mutation and resultant phenotype to be viewed more clearly. This article summarizes the current situation regarding syndromic craniosynostosis, highlights the complementarity of clinical, cytogenetic and molecular approaches that have contributed to the improved understanding of the genetic basis of craniosynostosis, and considers the new challenges that have emerged.

Hands and feet in the Apert syndrome

We studied 44 pairs of hands and 37 pairs of feet in Apert syndrome, utilizing clinical, dermatoglyphic, and radiographic methods. We also studied histologic sections of the hand from a 31-week stillborn fetus. Topic headings discussed include: clinical classification of syndactyly; correlations between types of hands and feet in the same patient; dermatoglyphics; anatomy of the hand; radiologic assessment; comparison with other studies; histologic assessment of the hand; acrocephalosyndactyly vs. acrocephalopolysyndactyly: a pseudodistinction; and some generalizations.

Gorlin-Chaudhry-Moss or Saethre-Chotzen syndrome?

We report a 2-year-old girl with craniosynostosis, an ossification defect of the cranial vault, midface hypoplasia, low frontal hairline, anti-mongoloid slant of the palpebral fissures, ptosis of the lateral upper lids and high-arched narrow palate. There are additional findings fitting the Gorlin-Chaudhry-Moss syndrome, such as hypoplasia of the labia majora, hypoplasia of the distal phalanges of fingers and toes and conductive hearing loss, but hypertrichosis and dental anomalies are missing, which were described in the four females previously reported with the probably autosomal recessive Gorlin-Chaudhry-Moss syndrome. Since the autosomal dominant Saethre-Chotzen syndrome may show similar cranio-facial features, short fingers with non-obligatory cutaneous syndactyly, and ossification defects of the cranial vault, the Saethre-Chotzen syndrome should also be considered in our patient.

Isolation of the human MOX2 homeobox gene and localization to chromosome 7p22.1-p21.3

We have isolated and characterized cDNA clones encoding a novel human homeobox gene, MOX2, the homologue of the murine mox-2 gene. The MOX2 protein contains all of the characteristic features of Mox-2 proteins of other vertebrate species, namely the homeobox, the polyhistidine stretch, and a number of potential serine/threonine phosphorylation sites. The homeodomain of MOX2 protein is identical to all other vertebrate species reported so far (rodents and amphibians). Outside the homeodomain, Mox-2 proteins share a high degree of identity, except for a few amino acid differences encountered between the human and the rodent polypeptides. A polyhistidine stretch of 12 amino acids in the N terminal region of the protein is also conserved among humans, rodents, and (only partly) amphibians. The chromosomal position of MOX2 was assigned to 7p22.1-p21.3.

Saethre-Chotzen syndrome associated with balanced translocations involving 7p21: three further families

We describe three families segregating different reciprocal chromosome translocations, t(7;18)(p21.2;q23), t(2;7)(q21.1;p21.2), and t(5;7)(p15.3;p21.2). A total of seven apparently balanced carriers have been identified and all manifest features of the Saethre-Chotzen syndrome, although only two have overt craniosynostosis. In one family the carriers are immediately recognisable by their unusual ears, and clefts of the hard or soft palate are present in all three families. These observations extend previous linkage and cytogenetic evidence that a locus for Saethre-Chotzen syndrome resides in band 7p21.2.

The breakpoint on 7p in a patient with t(6;7) and craniosynostosis is spanned by a YAC clone containing the D7S503 locus

We previously reported a patient with an apparently balanced t(6;7) translocation and craniosynostosis. We now demonstrate, by fluorescence in situ hybridization, that the yeast artificial chromosome clone 933-e-1 from the Centre d'Etude du Polymorphisme Humain library harbouring the D7S503 locus spans the breakpoint on distal 7p. Recent reports have defined a candidate region for a Saethre-Chotzen craniosynostosis locus between the loci D7S513 and D7S516, a region that includes the D7S503 locus. Since the translocation carrier shows only some of the symptoms characteristic for the Saethre-Chotzen syndrome, it remains unresolved whether the gene disrupted by the translocation event is the only one causing craniosynostosis in this chromosomal region.

Genetic study of nonsyndromic coronal craniosynostosis

From a series of 1265 individuals with different craniosynostoses hospitalized between 1976 and 1993, 260 probands with nonsyndromic unilateral (181) or bilateral (79) coronal synostosis were analysed. The prevalence of craniosynostoses was estimated as 1 in 2100 children. In the group of coronal synostosis, family history was obtained on 192 probands in 180 pedigrees. The male:female ratio was 1:2. The average paternal age was 32.7 +/- 6.4 years, which is significantly higher than normal. In 26 of the 180 pedigrees, a high degree of familial aggregation was observed, giving a 14.4% figure of familial cases. The bicoronal synostoses were significantly more often familial than the unicoronal synostoses. Segregation analysis of these families leads to the conclusion that coronal synostosis is transmitted as a dominant disorder with 0.60 penetrance and 61% of sporadic cases.

Evidence that the Saethre-Chotzen syndrome locus lies between D7S664 and D7S507, by genetic analysis and detection of a microdeletion in a patient

The locus for Saethre-Chotzen syndrome, a common autosomal dominant disorder of craniosynostosis and digital anomalies, was previously mapped to chromosome 7p between D7S513 and D7S516. We used linkage and haplotype analyses to narrow the disease locus to an 8-cM region between D7S664 and D7S507. The tightest linkage was to locus D7S664 (Z = 7.16, theta = .00). Chromosomes from a Saethre-Chotzen syndrome patient with t(2;7) (p23;p22) were used for in situ hybridization with YAC clones containing D7S664 and D7S507. The D7S664 locus was found to lie distal to the 7p22 breakpoint, and the D7S507 locus was deleted from the translocation chromosomes. These genetic and physical mapping data independently show that the disease locus resides in this interval.

Mutations in the fibroblast growth factor receptor 2 gene cause Crouzon syndrome

Crouzon syndrome is an autosomal dominant condition causing premature fusion of the cranial sutures (craniosynostosis) and maps to chromosome 10q25-q26. We now present evidence that mutations in the fibroblast growth factor receptor 2 gene (FGFR2) cause Crouzon syndrome. We found SSCP variations in the B exon of FGFR2 in nine unrelated affected individuals as well as complete cosegregation between SSCP variation and disease in three unrelated multigenerational families. In four sporadic cases, the normal parents did not have SSCP variation. Finally, direct sequencing has revealed specific mutations in the B exon in all nine sporadic and familial cases, including replacement of a cysteine in an immunoglobulin-like domain in five patients.