Cytogenetic evidence that the Saethre-Chotzen gene maps to 7p21.2

Results from Genetic Studies in Patients Affected with Craniosynostosis: Clinical and Molecular Aspects

Background: Craniosynostosis (CS) represents a highly heterogeneous genetic condition whose genetic background has not been yet revealed. The abnormality occurs either in isolated form or syndromic, as an element of hundreds of different inborn syndromes. Consequently, CS may often represent a challenging diagnostic issue.

Methods: We investigated a three-tiered approach (karyotyping, Sanger sequencing, followed by custom gene panel/chromosomal microarray analysis, and exome sequencing), coupled with prioritization of variants based on dysmorphological assessment and description in terms of human phenotype ontology. In addition, we have also performed a statistical analysis of the obtained clinical data using the nonparametric test χ².

Results: We achieved a 43% diagnostic success rate and have demonstrated the complexity of mutations’ type harbored by the patients, which were either chromosomal aberrations, copy number variations, or point mutations. The majority of pathogenic variants were found in the well-known CS genes, however, variants found in genes associated with chromatinopathies or RASopathies are of particular interest.

Conclusion: We have critically summarized and then optimised a cost-effective diagnostic algorithm, which may be helpful in a daily diagnostic routine and future clinical research of various CS types. Moreover, we have pinpointed the possible underestimated co-occurrence of CS and intellectual disability, suggesting it may be overlooked when intellectual disability constitutes a primary clinical complaint. On the other hand, in any case of already detected syndromic CS and intellectual disability, the possible occurrence of clinical features suggestive for chromatinopathies or RASopathies should also be considered.

New locus underlying auriculocondylar syndrome (ARCND): 430 kb duplication involving TWIST1 regulatory elements

Background

Auriculocondylar syndrome (ARCND) is a rare genetic disease that affects structures derived from the first and second pharyngeal arches, mainly resulting in micrognathia and auricular malformations. To date, pathogenic variants have been identified in three genes involved in the EDN1-DLX5/6 pathway (PLCB4, GNAI3 and EDN1) and some cases remain unsolved. Here we studied a large unsolved four-generation family.

Methods

We performed linkage analysis, resequencing and Capture-C to investigate the causative variant of this family. To test the pathogenicity of the CNV found, we modelled the disease in patient craniofacial progenitor cells, including induced pluripotent cell (iPSC)-derived neural crest and mesenchymal cells.

Results

This study highlights a fourth locus causative of ARCND, represented by a tandem duplication of 430 kb in a candidate region on chromosome 7 defined by linkage analysis. This duplication segregates with the disease in the family (LOD score=2.88) and includes HDAC9, which is located over 200 kb telomeric to the top candidate gene TWIST1. Notably, Capture-C analysis revealed multiple cis interactions between the TWIST1 promoter and possible regulatory elements within the duplicated region. Modelling of the disease revealed an increased expression of HDAC9 and its neighbouring gene, TWIST1, in neural crest cells. We also identified decreased migration of iPSC-derived neural crest cells together with dysregulation of osteogenic differentiation in iPSC-affected mesenchymal stem cells.

Conclusion

Our findings support the hypothesis that the 430 kb duplication is causative of the ARCND phenotype in this family and that deregulation of TWIST1 expression during craniofacial development can contribute to the phenotype.

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.

The frequency of palatal anomalies in Saethre-Chotzen syndrome

OBJECTIVE

Saethre-Chotzen Syndrome (SCS) is an autosomal dominant disorder with widespread phenotypic variability. Cardinal features include coronal synostosis, blepharoptosis, and limb abnormalities. Cleft palate can also occur, but there are few reports on its frequency. This study was undertaken to determine the prevalence of palatal anomalies in this population.

DESIGN

We retrospectively reviewed the records of 51 patients with SCS seen at Children's Hospital Boston over the past 30 years. Palatal findings in our patients were compared with those in the literature. To illustrate the phenotypic variability in SCS, we describe an unusual infant who presented for evaluation of cleft palate and blepharoptosis. Her father had only blepharoptosis; this was the clue to the diagnosis, which was confirmed by finding a deletion in the TWIST gene.

RESULTS

In our patients, high-arched palate was noted in 43%, bifid uvula in 10%, and cleft palate in 6%. These figures differed slightly from the combined percentages in published reports: 24% with high-arched palate, 2% with bifid uvula, and 5% with cleft palate.

CONCLUSIONS

Palatal anomalies are relatively common in SCS. This entity should be considered in the differential diagnosis of a child with cleft palate, particularly in the presence of blepharoptosis, nasal deviation, and limb abnormalities in the patient or in family members.

Bipolar affective disorder associated with 11q24.2 disruption—A second report

A recent report identified bipolar affective disorder in a patient with a de novo deletion 11q24.2. We record a further instance involving this cytogenetic region and bipolar affective disorder in a patient with a balanced translocation.

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.

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.

Postnatal onset of craniosynostosis in a case of Saethre-Chotzen syndrome

Saethre-Chotzen syndrome is a craniosynostosis syndrome characterized by facial and limb abnormalities. It is caused by mutations in the TWIST gene on chromosome 7p21. To date, more than 80 different mutations in TWIST have been reported in the literature.Recently, large deletions of chromosome 7p, encompassing the TWIST locus, have been detected in patients with clinical features of Saethre-Chotzen syndrome. Strikingly, all these patients were severely mentally retarded, which is otherwise a rare finding in Saethre-Chotzen syndrome. The authors report a patient with a large TWIST/7p deletion but with normal development. Furthermore, craniosynostosis was not present at birth or at the age of 4 months. However, skull radiographs taken at the age of 14 months showed stenosis of both coronal sutures, as well as of part of the sagittal suture. Reports on postnatal onset of craniosynostosis have been made in Crouzon syndrome but, to the authors' knowledge, never in Saethre-Chotzen syndrome.

Zimmermann-Laband syndrome associated with a balanced reciprocal translocation t(3;8)(p21.2;q24.3) in mother and daughter: molecular cytogenetic characterization of the breakpoint regions

Zimmermann-Laband syndrome (ZLS) is a rare disorder characterized by gingival fibromatosis, abnormalities of the nose and/or ears, and absence or hypoplasia of nails or terminal phalanges of hands and feet. Other more variable features include hyperextensibility of joints, hepatosplenomegaly, mild hirsutism, and mental retardation. The genetic basis of ZLS is unknown; autosomal dominant inheritance has been suggested. We report an apparently balanced chromosomal aberration, 46,XX, t(3;8)(p13-p21.2;q24.1-q24.3), in a family with an affected mother and daughter. Using fluorescence in situ hybridization with BAC clones, we refined the breakpoints to 3p21.2 and 8q24.3 and, thereby, narrowed down both breakpoint regions to approximately 1.5 Mb. Our data provide additional support to the assumption that ZLS follows autosomal dominant inheritance. The 3;8 translocation described here represents a powerful resource to identify the causative gene for ZLS that maps most likely to one of the breakpoints.

Facial dysgenesis: a novel facial syndrome with chromosome 7 deletion p15.1-21.1

We describe a female neonate with a unique constellation of features including anophthalmia and cryptophthalmos, temporal remnant "eye tags," bilateral cleft lip, unilateral cleft palate, a proboscis with absent nasal septum, choanal atresia, micrognathia, square stoma, and bilateral external auditory canal atresia. Gross brain structure, pituitary function, limbs, trunk, and genitalia were normal. Skeletal survey, echocardiogram and abdominal viscera were unremarkable except for a split central sinus of the right kidney. BAER exam indicated she could hear and temporal CT confirmed the presence of cochlea and possible ossicles. Cytogenetic evaluation revealed an interstitial deletion at chromosome 7p15.1-21.1. TWIST, a gene encoding a transcription factor involved in craniofacial development, is deleted by FISH analysis. The absence of a mutation on the non-deleted allele of TWIST as determined by sequencing virtually eliminates complete loss of the TWIST gene as the cause of this patient's severe phenotype. The HOXA gene cluster also encodes transcription factors that are crucial for directing cephalad to caudad somatic fetal development. HOXA1, the most telomeric of the 13 members of the HOXA gene cluster, is located at the centromeric boundary of the patient's chromosome 7 deletion. By FISH analysis, neither allele of HOXA1 is deleted and sequencing reveals no mutations. Haploinsufficiency or complete loss of the HOXA1 gene also does not appear to cause this patient's severe phenotype. Previous reports of chromosome 7p15-21 deletions do not have phenotypes similar to this patient.

Genetic analysis of patients with the Saethre-Chotzen phenotype

Saethre-Chotzen syndrome is a common craniosynostosis syndrome characterized by craniofacial and limb anomalies. Intragenic mutations of the TWIST gene within 7p21 have been identified as a cause of this disorder. There is phenotypic overlap with other craniosynostosis syndromes, and intragenic mutations in FGFR2 (fibroblast growth factor receptor 2) and FGFR3 (fibroblast growth factor receptor 3) have been demonstrated in the other conditions. Furthermore, complete gene deletions of TWIST have also been found in a significant proportion of patients with Saethre-Chotzen syndrome. We investigated 11 patients clinically identified as having the Saethre-Chotzen phenotype and 4 patients with craniosynostosis but without a clear diagnosis. Of the patients with the Saethre-Chotzen phenotype, four were found to carry the FGFR3 P250R mutation, three were found to be heterozygous for three different novel mutations in the coding region of TWIST, and two were found to have a deletion of one copy of the entire TWIST gene. Developmental delay was a distinguishing feature of the patients with deletions, compared to patients with intragenic mutations of TWIST, in agreement with the results of Johnson et al. [1998: Am J Hum Genet 63:1282-1293]. No mutations were found for the four patients with craniosynostosis without a clear diagnosis. Therefore, 9 of our 11 patients (82%) with the Saethre-Chotzen phenotype had detectable genetic changes in FGFR3 or TWIST. We propose that initial screening for the FGFR3 P250R mutation, followed by sequencing of TWIST and then fluorescence in situ hybridization (FISH) for deletion detection of TWIST, is sufficient to detect mutations in > 80% of patients with the Saethre-Chotzen phenotype.

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.

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.

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.

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.

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.

Duplication of 7p: further delineation of the phenotype and restriction of the critical region to the distal part of the short arm

We report on a patient with duplication of 7p15-->pter and review the literature. Patients with partial duplication of the distal 7p, including only the distal segment 7p15-->pter, have a syndrome comparable to that of patients with a larger or complete duplication of 7p. This suggests that the critical region for the dup(7p) phenotype is restricted to 7p15-->pter. The complete clinical phenotype of dup(7)(p15-->pter) includes mental retardation, skull anomalies, large anterior fontanel, cardiovascular defects, joint dislocation and contraction, and gastrointestinal and genital defects. Recognition of the clinical spectrum in patients with a smaller duplication of 7p, and the assignment of this critical region, should prove valuable for accurate counseling, prediction of outcome, and further gene mapping.

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.

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.

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.

Saethre-Chotzen syndrome

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Crouzon syndrome is not linked to craniosynostosis loci at 7p and 5qter

Evidence for linkage has been sought, in four pedigrees with Crouzon syndrome, between polymorphic markers known to be linked to the Saethre-Chotzen locus on 7p and another form of autosomal dominant craniosynostosis on 5q. The data we present exclude Crouzon syndrome as an allelic variant at either of these known craniosynostosis loci.