Novel mutation in the FGFR2 gene at the same codon as the Crouzon syndrome mutations in a severe Pfeiffer syndrome type 2 case

The genetic basis of hydrocephalus: genes, pathways, mechanisms, and global impact

Hydrocephalus (HC) is a heterogenous disease characterized by alterations in cerebrospinal fluid (CSF) dynamics that may cause increased intracranial pressure. HC is a component of a wide array of genetic syndromes as well as a secondary consequence of brain injury (intraventricular hemorrhage (IVH), infection, etc.) that can present across the age spectrum, highlighting the phenotypic heterogeneity of the disease. Surgical treatments include ventricular shunting and endoscopic third ventriculostomy with or without choroid plexus cauterization, both of which are prone to failure, and no effective pharmacologic treatments for HC have been developed. Thus, there is an urgent need to understand the genetic architecture and molecular pathogenesis of HC. Without this knowledge, the development of preventive, diagnostic, and therapeutic measures is impeded. However, the genetics of HC is extraordinarily complex, based on studies of varying size, scope, and rigor. This review serves to provide a comprehensive overview of genes, pathways, mechanisms, and global impact of genetics contributing to all etiologies of HC in humans.

MECOM-related disorder: Radioulnar synostosis without hematological aberration due to unique variants

PURPOSE

The etiology for a considerable proportion of patients with congenital radioulnar synostosis (RUS) remains unclear. This study aimed to investigate the genetic cause of RUS without a known cause.

METHODS

Patients with RUS were investigated. Exome sequencing and/or Sanger sequencing was performed. Bioinformatics analysis was also performed. Pathogenicity was evaluated for variants of interest.

RESULTS

We identified unique missense variants in MECOM (encodes EVI1) associated with RUS in 8 families. Of them, 6 families had variants in residue R781, including 3 families with R781C (c.2341C>T), 2 families with R781H (c.2342G>A), and 1 family with R781L (c.2342G>T). Another 2 variants included I783T (c.2348T>C) in 1 family and Q777E (c.2329C>G) in 1 family. All these variants were clustered within the ninth zinc finger motif of EVI1. Phenotype evaluation identified that most of these patients with RUS harboring mutant MECOM had finger malformations, but none of them had identifiable hematological abnormalities. Functional experiments showed that MECOM R781C led to alterations in TGF-β-mediated transcriptional responses.

CONCLUSION

This study examined MECOM variants by focusing on RUS instead of hematological abnormalities. The R781 residue in EVI1 is a hotspot for human RUS variants. Mutant MECOM is the second most common cause for familial RUS.

A genotype and phenotype analysis of SMAD6 mutant patients with radioulnar synostosis

Background

SMAD6 variants have been reported in patients with radioulnar synostosis (RUS). This study aimed to investigate the genotypes and phenotypes for a large cohort of patients with RUS having mutant SMAD6.

Methods

Genomic DNA samples were isolated from 251 RUS sporadic patients (with their parents) and 27 RUS pedigrees. Sanger sequencing was performed for the SMAD6 coding regions. For positive probands, co‐segregation and parental‐origin analysis of SMAD6 variants and phenotypic re‐evaluation were performed for their family members.

Results

We identified 50 RUS probands with SMAD6 variants (13 co‐segregated with RUS in pedigrees and 37 in RUS‐sporadic patients). Based on the new and previous data, we identified SMAD6 mutated in 16/38 RUS pedigrees and 61/393 RUS sporadic patients, respectively. Overall, 93 SMAD6 mutant patients with RUS were identified, among which 29 patients had unilateral RUS, where the left side was more involved than the right side (left:right = 20:9). Female protective effects and non‐full penetrance were observed, in which only 6.90% mothers (vs. ~50% fathers) of SMAD6 mutant RUS probands had RUS. Pleiotropy was observed as a re‐evaluation of SMAD6 mutant families identified: (a) three families had axial skeletal malformations; (b) two families had polydactyly; and (c) eight families had other known malformations.

Conclusion

SMAD6 was mutated in 42.11% RUS pedigrees and 15.52% RUS sporadic patients.

The RUS patients with SMAD6 variants exhibit both non‐full‐penetrance, variable expressivity, pleiotropy, female protective effects, and the left side is more susceptible than the right side.

Prenatal diagnosis of Pfeiffer syndrome type 2 with increased nuchal translucency

Pfeiffer syndrome (PS) is a rare autosomal dominant genetic disorder characterized by craniosynostosis, broad thumbs / toes. Here, we report a case of PS type 2 with increased nuchal translucency in early trimester.

Pfeiffer type 2 syndrome: review with updates on its genetics and molecular biology

INTRODUCTION

Pfeiffer syndrome is a rare autosomal dominant inherited disorder associated with craniosynostosis, midfacial hypoplasia, and broad thumbs and toes. The syndrome has been divided into three clinical subtypes based on clinical findings.

METHODS

This review will specifically examine the most severe type, Pfeiffer syndrome type 2, focusing on its genetics and molecular biology.

CONCLUSION

This subtype of the syndrome is caused by de novo sporadic mutations, the majority of which occur in the fibroblast growth factor receptor type 1 and 2 (FGFR1/2) genes. There is not one specific mutation, however. This disorder is genetically heterogeneous and may have varying phenotypic expressions that in various cases have overlapped with other similar craniosynostoses. A specific missense mutation of FGFR2 causing both Pfeiffer and Crouzon syndromes has been identified, with findings suggesting that gene expression may be affected by polymorphism within the same gene. Compared to other craniosynostosis-related disorders, Pfeiffer syndrome is the most extreme phenotype, as the underlying mutations cause wider effects on the secondary and tertiary protein structures and exhibit harsher clinical findings.

Pfeiffer type 2 syndrome: review with updates on its genetics and molecular biology

INTRODUCTION

Pfeiffer syndrome is a rare autosomal dominant inherited disorder associated with craniosynostosis, midfacial hypoplasia, and broad thumbs and toes. The syndrome has been divided into three clinical subtypes based on clinical findings.

METHODS

This review will specifically examine the most severe type, Pfeiffer syndrome type 2, focusing on its genetics and molecular biology.

CONCLUSION

This subtype of the syndrome is caused by de novo sporadic mutations, the majority of which occur in the fibroblast growth factor receptor type 1 and 2 (FGFR1/2) genes. There is not one specific mutation, however. This disorder is genetically heterogeneous and may have varying phenotypic expressions that in various cases have overlapped with other similar craniosynostoses. A specific missense mutation of FGFR2 causing both Pfeiffer and Crouzon syndromes has been identified, with findings suggesting that gene expression may be affected by polymorphism within the same gene. Compared to other craniosynostosis-related disorders, Pfeiffer syndrome is the most extreme phenotype, as the underlying mutations cause wider effects on the secondary and tertiary protein structures and exhibit harsher clinical findings.

C278F mutation in FGFR2 gene causes two different types of syndromic craniosynostosis in two Chinese patients

The current study was performed with aim to investigate the fibroblast growth factor receptor 2 (FGFR2) gene in two Chinese families with two different forms of syndromic craniosynostosis, and to characterize their associated clinical features. Two families underwent complete ophthalmic examinations, and two patients from each family were diagnosed with craniosynostosis. Genomic DNA was extracted from leukocytes of peripheral blood collected from these two families and from 200 unrelated subjects within the same population as controls. Exons 8 and 10 of the FGFR2 gene were amplified by polymerase chain reaction and directly sequenced. Ophthalmic examinations of the two patients revealed shallow orbits and ocular proptosis, accompanied by midface hypoplasia and craniosynostosis. Case 1 had retinal detachment, abnormal limbs and hands, while case 2 exhibited normal hands and feet upon clinical examination. A heterozygous FGFR2 missense mutation c.833G>T (C278F) in exon 8 was identified in these two patients, but not in unaffected family members or the normal controls. Although FGFR2 gene mutations and polymorphisms have been studied in various ethnic groups, we report a mutation of FGFR2 in two different Chinese patients with two different types of syndromic craniosynostosis.

A de novo missense mutation of FGFR2 causes facial dysplasia syndrome in Holstein cattle

Background

Surveillance for bovine genetic diseases in Denmark identified a hitherto unreported congenital syndrome occurring among progeny of a Holstein sire used for artificial breeding. A genetic aetiology due to a dominant inheritance with incomplete penetrance or a mosaic germline mutation was suspected as all recorded cases were progeny of the same sire. Detailed investigations were performed to characterize the syndrome and to reveal its cause.

Results

Seven malformed calves were submitted examination. All cases shared a common morphology with the most striking lesions being severe facial dysplasia and complete prolapse of the eyes. Consequently the syndrome was named facial dysplasia syndrome (FDS). Furthermore, extensive brain malformations, including microencephaly, hydrocephalus, lobation of the cerebral hemispheres and compression of the brain were present. Subsequent data analysis of progeny of the sire revealed that around 0.5% of his offspring suffered from FDS.

High density single nucleotide polymorphism (SNP) genotyping data of the seven cases and their parents were used to map the defect in the bovine genome. Significant genetic linkage was obtained for three regions, including chromosome 26 where whole genome sequencing of a case-parent trio revealed two de novo variants perfectly associated with the disease: an intronic SNP in the DMBT1 gene and a single non-synonymous variant in the FGFR2 gene. This FGFR2 missense variant (c.927G>T) affects a gene encoding a member of the fibroblast growth factor receptor family, where amino acid sequence is highly conserved between members and across species. It is predicted to change an evolutionary conserved tryptophan into a cysteine residue (p.Trp309Cys). Both variant alleles were proven to result from de novo mutation events in the germline of the sire.

Conclusions

FDS is a novel genetic disorder of Holstein cattle. Mutations in the human FGFR2 gene are associated with various dominant inherited craniofacial dysostosis syndromes. Given the phenotypic similarities in FDS affected calves, the genetic mapping and absence of further high impact variants in the critical genome regions, it is highly likely that the missense mutation in the FGFR2 gene caused the FDS phenotype in a dominant mode of inheritance.

Electronic supplementary material

The online version of this article (doi:10.1186/s12863-017-0541-3) contains supplementary material, which is available to authorized users.

Distinct selective forces and Neanderthal introgression shaped genetic diversity at genes involved in neurodevelopmental disorders

In addition to high intelligence, humans evolved specialized social-cognitive skills, which are specifically affected in children with autism spectrum disorder (ASD). Genes affected in ASD represent suitable candidates to study the evolution of human social cognition. We performed an evolutionary analysis on 68 genes associated to neurodevelopmental disorders; our data indicate that genetic diversity was shaped by distinct selective forces, including natural selection and introgression from archaic hominins. We discuss the possibility that segregation distortion during spermatogenesis accounts for a subset of ASD mutations. Finally, we detected modern-human-specific alleles in DYRK1A and TCF4. These variants are located within regions that display chromatin features typical of transcriptional enhancers in several brain areas, strongly suggesting a regulatory role. These SNPs thus represent candidates for association with neurodevelopmental disorders, and await experimental validation in future studies.

FGFR-associated craniosynostosis syndromes and gastrointestinal defects

Craniosynostosis is a relatively common birth defect characterized by the premature fusion of one or more cranial sutures. Examples of craniosynostosis syndromes include Crouzon (CS), Pfeiffer (PS), and Apert (AS) syndrome, with clinical characteristics such as midface hypoplasia, hypertelorism, and in some cases, limb defects. Mutations in Fibroblast Growth Factor Receptor-2 comprise the majority of known mutations in syndromic forms of craniosynostosis. A number of clinical reports of FGFR-associated craniosynostosis patients and mouse mutants have been linked to gastrointestinal tract (GIT) disorders, leading to the hypothesis of a direct link between FGFR-associated craniosynostosis syndromes and GIT malformations. We conducted an investigation to determine GIT symptoms in a sample of FGFR-associated craniosynostosis syndrome patients and a mouse model of CS containing a mutation (W290R) in Fgfr2. We found that, compared to the general population, the incidence of intestinal/bowel malrotation (IM) was present at a higher level in our sample population of patients with FGFR-associated craniosynostosis syndromes. We also showed that the mouse model of CS had an increased incidence of cecal displacement, suggestive of IM. These findings suggest a direct relationship between FGFR-related craniosynostosis syndromes and GIT malformations. Our study may shed further light on the potential widespread impact FGFR mutations on different developmental systems. Based on reports of GIT malformations in children with craniosynostosis syndromes and substantiation with our animal model, GIT malformations should be considered in any child with an FGFR2-associated craniosynostosis syndrome. © 2016 Wiley Periodicals, Inc.

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.

Visualizing the origins of selfish de novo mutations in individual seminiferous tubules of human testes

De novo point mutations arise predominantly in the male germline and increase in frequency with age, but it has not previously been possible to locate specific, identifiable mutations directly within the seminiferous tubules of human testes. Using microdissection of tubules exhibiting altered expression of the spermatogonial markers MAGEA4, FGFR3, and phospho-AKT, whole genome amplification, and DNA sequencing, we establish an in situ strategy for discovery and analysis of pathogenic de novo mutations. In 14 testes from men aged 39-90 y, we identified 11 distinct gain-of-function mutations in five genes (fibroblast growth factor receptors FGFR2 and FGFR3, tyrosine phosphatase PTPN11, and RAS oncogene homologs HRAS and KRAS) from 16 of 22 tubules analyzed; all mutations have known associations with severe diseases, ranging from congenital or perinatal lethal disorders to somatically acquired cancers. These results support proposed selfish selection of spermatogonial mutations affecting growth factor receptor-RAS signaling, highlight its prevalence in older men, and enable direct visualization of the microscopic anatomy of elongated mutant clones.

Upper extremity anomalies in Pfeiffer syndrome and mutational correlations

BACKGROUND

Pfeiffer syndrome is characterized by craniosynostosis and a variety of associated upper and lower extremity anomalies. The authors reviewed presentation and treatment of upper extremity anomalies in a series of genotyped patients with Pfeiffer syndrome.

METHODS

Medical records of patients with Pfeiffer syndrome seen at the authors' institution over a 16-year period were reviewed. Data on clinical presentation, genetic testing, and treatment were collected. The upper extremity anomalies were documented using plain radiographs and physical examinations by a multidisciplinary craniofacial team.

RESULTS

Of 15 patients identified as having FGFR1- or FGFR2-confirmed Pfeiffer syndrome, 12 (80 percent) presented with upper extremity anomalies, most commonly broad thumbs [n = 10 (83 percent)], radial clinodactyly (thumbs) [n = 7 (58 percent)], and symphalangism [n = 7 each (58 percent)]. All patients with upper extremity anomalies had lower extremity anomalies. Six of the 12 patients (50 percent) with upper extremity findings underwent surgical correction. FGFR1 or FGFR2 genotype did not correlate with upper extremity phenotype.

CONCLUSIONS

Although broad thumbs are common, patients with Pfeiffer syndrome often present with other upper extremity anomalies that may not require surgical intervention. Genetic and allelic heterogeneity may explain phenotypic variability in these upper extremity anomalies. Characterization of these limb differences should be made by pediatric hand surgeons as part of a craniofacial team. Treatment decisions should be individualized and dictated by the type and severity of clinical presentation.

CLINICAL QUESTION/LEVEL OF EVIDENCE

Risk, IV.

NADPH P450 oxidoreductase: structure, function, and pathology of diseases

Cytochrome P450 oxidoreductase (POR) is an enzyme that is essential for multiple metabolic processes, chiefly among them are reactions catalyzed by cytochrome P450 proteins for metabolism of steroid hormones, drugs and xenobiotics. Mutations in POR cause a complex set of disorders that often resemble defects in steroid metabolizing enzymes 17α-hydroxylase, 21-hydroxylase and aromatase. Since our initial reports of POR mutations in 2004, more than 200 different mutations and polymorphisms in POR gene have been identified. Several missense variations in POR have been tested for their effect on activities of multiple steroid and drug metabolizing P450 proteins. Mutations in POR may have variable effects on different P450 partner proteins depending on the location of the mutation. The POR mutations that disrupt the binding of co-factors have negative impact on all partner proteins, while mutations causing subtle structural changes may lead to altered interaction with specific partner proteins and the overall effect may be different for each partner. This review summarizes the recent discoveries related to mutations and polymorphisms in POR and discusses these mutations in the context of historical developments in the discovery and characterization of POR as an electron transfer protein. The review is focused on the structural, enzymatic and clinical implications of the mutations linked to newly identified disorders in humans, now categorized as POR deficiency.

Involvement of the WNT and FGF signaling pathways in non-isolated anorectal malformations: sequencing analysis of WNT3A, WNT5A, WNT11, DACT1, FGF10, FGFR2 and the T gene

Anorectal malformations (ARMs) comprise a broad spectrum of anomalies, including anal atresia, congenital anal fistula and persistence of the cloaca. Research suggests that genetic factors play an important role in ARM development. However, few genetic variants have been identified. Embryogenesis is orchestrated by crosstalk of the wingless-type MMTV integration site family (WNT) and fibroblast growth factor (FGF) signaling pathways in a process that involves several intracellular cascades. Studies in mice have implicated several genes from these pathways in the etiology of ARMs. We performed sequencing analysis of seven of these previously reported genes in 78 patients with ARMs occurring within the context of at least one additional congenital anomaly. No associations were identified with variants in WNT3A, WNT5A, WNT11, DACT1, FGF10 or the T gene. In the FGFR2 gene, three novel heterozygous nucleotide substitutions were identified. Further investigations, including the study of family members, revealed that these variants were not causally related to the phenotype in the present ARM cohort. Mutations in the seven investigated genes may nonetheless be a cause of ARMs in rare cases. However, further studies should consider genes encoding other proteins in the WNT/FGF signaling pathways as possible candidates.

The Fgfr2 W290R mouse model of Crouzon syndrome

PURPOSE

This study aimed to review and discuss the utility of the Fgfr2 (W290R) mouse mutant as a model of human Crouzon syndrome.

METHODS

A review of current and past scientific literature on Fibroblast Growth Factor Receptor-2 (FGFR2) protein domain structure, FGFR mutations associated with human Crouzon syndrome, and phenotypic and molecular changes combined with recent observations and experimental data of the Fgfr2 (W290R) mouse mutant was conducted. A comparison of the Fgfr2 (W290R) mouse mutant with another mouse model of Crouzon syndrome, Fgfr2 (C342R) mouse mutant, was also performed. Finally, possible future research directions using the Fgfr2 (W290R) mutant mice were discussed.

RESULTS

The Fgfr2 (W290R) heterozygous mouse exhibits defects characteristic of human Crouzon syndrome. At the molecular level, the defects observed in the mouse mutant are due to the dysregulation of signaling of both the IIIb and IIIc isoforms of Fgfr2. The involvement of the IIIb isoform of FGFR2 in the etiopathology of Crouzon syndrome is a novel finding in the craniosynostosis literature field. Dysregulated signaling of both IIIb and IIIc isoforms causes a broad spectrum of changes that explain some of the defects observed clinically in humans. Several of the defects observed in the Fgfr2 (W290R) homozygous mouse mutant are attributable to a loss-of-function mechanism in contrast to the frequently reported gain-of-function receptor function associated with mutated FGF receptors in craniosynostosis.

CONCLUSIONS

The Fgfr2 ( W290R ) mouse model can be used as a model system to further investigate the cellular, molecular, and biochemical mechanisms of Crouzon syndrome.

A case report of a patient with Pfeiffer syndrome, an FGRF 2 mutation (Trp290Cys) and unique ocular anterior segment findings

PURPOSE

To report a case of a child with Pfeiffer syndrome, unique ocular anterior segment findings and a mutation in FGFR2 (Trp290Cys).

METHODS

Case Report.

RESULTS

We describe a patient with Pfeiffer syndrome with a unique constellation of ocular anterior segment anomalies including microcornea, limbal scleralization, corectopia and glaucoma. Genomic DNA extraction was heterozygous for a G to T mutation at nucleotide 870 of the fibroblast growth factor receptor 2 gene (FGFR2) which changes tryptophan (TGG) to cysteine (TGT) at amino acid position 290 (Trp290Cys).

CONCLUSION

This case supports the association between Pfeiffer syndrome and severe ocular anterior segment anomalies, including glaucoma, and underscores the possible role that FGFR2 has in development of the anterior segment of the eye.

Genetic variation in human P450 oxidoreductase

Catalysis by all 50 Type II (microsomal) P450 enzymes, including steroidogenic P450c17, P450c21, and P450aro and hepatic drug-metabolizing enzymes requires electron donation from P450 oxidoreductase (POR). POR knockout mice are embryonic lethal, but human POR mutations cause a complex disorder of steroidogenesis. Disorders of hepatic drug metabolism in human POR deficiency have not yet been described. To understand the potential contribution of POR to pharmacogenetics, we sequenced the POR gene in 842 normal persons from 4 ethnic groups. We detected 140 single nucleotide sequence variants of which 43 were in >1% of alleles, including 15 missense mutants; this brings the total of known POR missense mutants to 35. A503V was found on 28% of alleles, varying from 19% in African Americans to 37% in Chinese Americans. We expressed all 35 missense mutants in E. coli and assayed their activities to: oxidize NADPH, reduce cytochrome c, support the 17alpha-hydroxylase and 17,20 lyase activities of bacterially expressed human P450c17, and support the metabolism of fluorogenic EOMCC by bacterially expressed human CYP1A2 and CYP2C19. These data show that there are great differences in the activities of some POR mutants depending on the electron recipient assayed; for example, Q153R causes severely impaired steroid biosynthesis in human patients and in vitro, but is a gain-of-function mutant with CYP1A2 and 2C19. A503V reduces both activities of P450c17 in half, but had no effect on CYP1A2 or 2C19. POR variants are a previously unappreciated source of genetic variation in patterns of steroid synthesis and drug metabolism.

The natural history of patients treated for FGFR3-associated (Muenke-type) craniosynostosis

BACKGROUND

Muenke-type craniosynostosis is defined as fibroblast growth factor receptor 3 (FGFR3)-associated coronal craniosynostosis with or without mental retardation. With complementary genetic information, more precise diagnosis and long-term functional outcome of cranial vault remodeling in affected patients can be studied, and additional distinct features of Muenke syndrome can now be investigated. This study was undertaken to assess craniofacial growth and long-term functional outcome in patients with Muenke-type craniosynostosis.

METHODS

A chart review of all FGFR3 patients at The Children's Hospital of Philadelphia who had undergone cranial vault remodeling for unicoronal or bicoronal synostosis (n = 16) was performed. Need for reoperation, midface surgery, and functional corrections were assessed. Audiology and orthodontic records were reviewed.

RESULTS

All patients underwent cranial remodeling during infancy. Repeated intracranial surgery was performed or is currently scheduled for aesthetic reasons only (n = 7). Sexual dimorphism with male preponderance in FGFR3 unicoronal synostosis was detected. Despite dental crowding amenable to palatal expansion in patients with bicoronal synostosis, significant midface hypoplasia was not observed. Sensorineural hearing loss with a distinctive pattern was present in all patients who had undergone audiology testing.

CONCLUSIONS

Patients with FGFR3-associated craniosynostosis demonstrate a sexual dimorphism, with a male preponderance for unicoronal synostosis. A secondary major intracranial procedure is required for recurrent supraorbital retrusion in at least 43 percent of patients. A secondary or tertiary extracranial forehead contouring procedure should be anticipated in nearly all patients. No patient required any midface correctional procedure. These patients demonstrate characteristic bilateral, symmetric, low- to mid-frequency sensorineural hearing loss.

P450 oxidoreductase deficiency: a new disorder of steroidogenesis

Microsomal P450 enzymes, which metabolize drugs and catalyze steroid biosynthesis require electron donation from NADPH via P450 oxidoreductase (POR). POR knockout mice are embryonically lethal, but we found recessive human POR missense mutations causing disordered steroidogenesis and Antley-Bixler syndrome (ABS), a skeletal malformation syndrome featuring craniosynostosis. Dominant mutations in exons 8 and 10 of fibroblast growth factor receptor 2 (FGFR2) cause phenotypically related craniosynostosis syndromes and were reported in patients with ABS and normal steroidogenesis. Sequencing POR and FGFR2 exons in 32 patients with ABS and/or hormonal findings suggesting POR deficiency showed complete genetic segregation of POR and FGFR2 mutations. Fifteen patients carried POR mutations on both alleles, four carried POR mutations on 1 allele, nine carried FGFR2/3 mutations on one allele and no mutation was found in three patients. The 34 affected POR alleles included 10 with A287P, 7 with R457H, 9 other missense mutations and 7 frameshifts. These 11 missense mutations and 10 others identified by database mining were expressed in E. coli, purified to apparent homogeneity, and their catalytic capacities were measured in four assays: reduction of cytochrome c, oxidation of NADPH, and support of the 17alpha-hydroxylase and 17,20 lyase activities of human P450c17. As assessed by Vmax/Km, 17,20 lyase activity provided the best correlation with clinical findings. Modeling human POR on the X-ray crystal structure of rat POR shows that these mutant activities correlate well with their locations in the structure. POR deficiency is a new disease, distinct from the craniosynostosis syndromes caused by FGFR mutations.

Mutation screening in patients with syndromic craniosynostoses indicates that a limited number of recurrent FGFR2 mutations accounts for severe forms of Pfeiffer syndrome

Crouzon Syndrome (CS), Pfeiffer syndrome (PS) and the phenotypically related Jackson-Weiss (JW) variant are three craniosynostotic conditions caused by heterozygous mutations in Fibroblast Growth Factor Receptor (FGFR) genes. Screening a large cohort of 84 patients with clinical features of CS, PS or JW by direct sequencing of genomic DNA, enabled FGFR1, 2 or 3 mutation detection in 79 cases. Mutations preferentially occurred in exons 8 and 10 of FGFR2 encoding the third Ig loop of the receptor. Among the 74 FGFR2 mutations that we identified, four were novel including three missense substitutions causing CS and a 2 bp deletion creating a premature stop codon and producing JW phenotype. Five FGFR2 mutations were found in one of the two tyrosine kinase subdomains and one in the Ig I loop. Interestingly, two FGFR2 mutations creating cysteine residues (W290C and Y340C) caused severe forms of PS while conversion of the same residues into another amino-acid (W290G/R, Y340H) resulted in Crouzon phenotype exclusively. Our data provide conclusive evidence that the mutational spectrum of FGFR2 mutations in CS and PS is wider than originally thought. Genotype-phenotype analyses based on our cohort and previous studies further indicate that in spite of some overlap, PS and CS are preferentially accounted for by two distinct sets of FGFR2 mutations. A limited number of recurrent amino-acid changes (W290C, Y340C, C342R and S351C) is commonly associated with the most severe Pfeiffer phenotypes of poor prognosis.

Further evidence of association between mutations inFGFR2 and syndromic craniosynostosis with sacrococcygeal eversion

BACKGROUND

Pfeiffer syndrome (PS; OMIM #101600) is an autosomal dominant disorder characterized by craniosynostosis, midface hypoplasia, broad thumbs, brachydactyly, broad great toes, and variable syndactyly.

CASE

We report a case of PS (type 3) with tracheal and visceral involvement and sacrococcygeal eversion. The patient shows facial dysmorphism with macrocephaly, dolichocephaly, and trigonocephaly, and an asymmetric skull, bilateral and severe exophthalmia with shallow orbits and ocular hypertelorism, downslanting palpebral fissures, constant strabismus, short anterior cranial base, and midface hypoplasia.

CONCLUSIONS

Molecular analysis of the FGFR2 gene in this patient revealed a point mutation (c.890G>C NM_000141). This mutation leads to the substitution of the residue tryptophan at position 290 to cysteine in the protein (p.Try290Cys). These data reinforce the hypothesis that the p.Trp290Cys mutation is more often associated with a severe and poor prognosis of PS. Furthermore they suggest that the presence of sacrococcygeal defects is not associated with any specific FGFR2 mutation.

P450 oxidoreductase deficiency: a new disorder of steroidogenesis affecting all microsomal P450 enzymes

Combined partial deficiency of 17alpha-hydroxylase and 21-hydroxylase activities was first described in 1985; however the genes for P450c17 and P450c21 in these patients lack mutations. In 1986 we postulated that this disorder might be due to mutations in P450 oxidoreductase (POR), the flavoprotein that donates electron to these and all other microsomal P450 enzymes, but this hypothesis was not tested until the POR gene sequence became available through the genome database. We found five POR missense mutations in our first four patients. In vitro assays of the activities of these mutations showed that the standard assay of POR activity, reduction of cytochrome c, correlated poorly with the patients' phenotypes, but that assays of POR-supported 17alpha-hydroxylase and 17,20 lyase activities correlated well. POR deficiency is a new disorder of adrenal and gonadal steroidogenesis that affects all microsomal cytochrome P450 enzymes, hence may have important implications for genetic differences in drug metabolism.

Abnormal steroidogenesis in three patients with Antley-Bixler syndrome: apparent decreased activity of 17alpha-hydroxylase, 17,20-lyase and 21-hydroxylase

BACKGROUND

Antley-Bixler syndrome (ABS) is characterized mainly by abnormal skeletal morphogenesis such as craniosynostosis and radiohumeral synostosis, and by ambiguous genitalia in some cases. The mechanisms resulting in these deformities have not been determined.

METHODS

The adrenal and gonadal function of three Japanese ABS patients were evaluated. Patient 1 (17-year-old-male) had bilateral cryptoorchidism, delayed puberty and symptoms of glucocorticoid deficiency. Patient 2 (14-year-old male) and patient 3 (4-year-old female) presented with emaciation. Additionally, patient 3 had partial labial fusion and common urogenital sinus. In each patient, blood sampling for steroid analysis before and after rapid adrenocorticotropic hormone (ACTH) stimulation was carried out. Additionally, urinary steroids were quantified. Molecular analysis of CYP17 and CYP21A2 were also performed.

RESULTS

All patients showed elevated basal 17alpha-deoxysteroid levels. Although the 17alpha-deoxysteroid levels further increased after rapid ACTH stimulation, 17alpha-hydroxysteroids including cortisol did not respond, suggesting impaired 17alpha-hydroxylation. Patient 1 and patient 2 showed low adrenal androgen blood levels both before and after rapid ACTH stimulation. Patient 3 showed lower than normal excretions of urinary androgens. Additionally, a prolonged ACTH stimulation in patient 3 failed to elicit significant increase of adrenal androgens. These findings suggested impaired 17,20-lyase activity. In contrast to attenuated 17alpha-hydroxycorticosteroids, notably cortisol, elevated 17alpha-hydroxyprogesterone (17OHP) levels were observed, not only in pubertal patients (1 and 2) but also in prepubertal patient 3, indicating impaired 21-hydroxylation. This assumption was supported by increased urinary 21-deoxycortisol metabolite excretion in patients 2 and 3. With the exception of a heterozygous mutation of CYP17 in one of the patients, other mutations of this gene or CYP21A2 were identified in any of the patients.

CONCLUSION

Combined decreased 17alpha-hydroxylation, 17,20-lyase activity and 21-hydroxylation was detected in three ABS patients. Considering that the enzymes responsible are all cytochrome P450 enzymes and that another cytochrome P450 enzyme, lanosterol 14alpha-demethylase, has recently been shown to be impaired in an ABS patient, we speculate that dysfunction of a system which commonly regulates cytochrome P 450 activity may be responsible for the ABS phenotype.

P450 oxidoreductase deficiency: a new disorder of steroidogenesis with multiple clinical manifestations

Combined partial deficiency of 17alpha-hydroxylase and 21-hydroxylase is well-described, but patients' genes for these enzymes lack mutations. Recent work has identified mutations in the gene for P450 oxidoreductase (POR) in such patients. POR-deficient individuals have a broad range of disorders, from infants with congenital malformations to women with the polycysic ovary syndrome. POR transfers electrons to all microsomal P450 enzymes: its deficiency affects steroidogenesis, drug metabolism and other processes.

Prenatal ultrasound diagnosis of a case of Pfeiffer syndrome without cloverleaf skull and review of the literature

Pfeiffer syndrome is characterized by bilateral coronal craniosynostosis, midface hypoplasia, beaked nasal tip, broad and medially deviated thumbs and great toes. Originally, it was described in eight persons from three generations in a pedigree consistent with an autosomal dominant transmission. Since then, several reports have documented its high clinical and genetic heterogeneity. The condition is usually detected in the newborn period or later, and very few prenatal ultrasound diagnoses have been reported. We present a case of Pfeiffer syndrome prenatally diagnosed at 20 weeks' gestation, in which the sonographic features of craniosynostosis, hypertelorism associated with an extreme proptosis, and broad thumb led to the diagnosis, confirmed after termination of pregnancy by dysmorphological, pathological and radiological evaluation. DNA analysis of the fibroblast growth factor receptor 2 (FGFR2) showed a missense mutation consisting in a transversion G --> C at nucleotide 870. This led to a Trp290Cys amino acidic substitution. We discuss the relevant findings of our and previously published cases. Our report demonstrates that a careful sonographic examination can lead to an early prenatal diagnosis of Pfeiffer syndrome also in cases without cloverleaf skull.

Compound heterozygous mutations of cytochrome P450 oxidoreductase gene (POR) in two patients with Antley-Bixler syndrome

Antley-Bixler syndrome (ABS) is characterized by skeletal defects including craniosynostosis and radiohumeral synostosis. Although mutations in the FGFR2 gene have been found in some patients called ABS, genetic heterogeneity of this syndrome has been proposed. We have previously reported three ABS patients with unique abnormalities in steroidogenesis (apparent decreased activity of 17alpha-hydroxylase, 17,20-lyase, and 21-hydroxylase). Decreased activity of lanosterol 14alpha-demethylase has also been described in an ABS patient. Since all these enzymes require cytochrome P450 oxidoreductase (encoded by POR) as an electron donor, we studied POR in two unrelated ABS patients with abnormal steroidogenesis. Direct sequencing of POR revealed that both patients had compound heterozygous mutations (1329insC and R454H in a male patient, 1698insC and R454H in a female patient). The two insertional mutations were assumed to generate truncated and unstable mRNAs. The R454H mutation was assumed to be deleterious because the R454 resides in the FAD-binding domain and is highly conserved among diverse species. Our results demonstrate that mutations in POR cause the ABS phenotype with autosomal recessive inheritance and with characteristic abnormalities in steroidogenesis.

FGFR2 mutation in a patient with Apert syndrome associated with humeroradial synostosis

Most cases of Apert syndrome are due to S252W or P253R mutations in the fibroblast growth factor receptor 2 (FGFR2) gene. Differences in the effects of S252W and P253R mutations on the clinical features of Apert syndrome have been studied, but little is known about the type of FGFR2 mutation in Apert syndrome with humeroradial synostosis. To study a correlation between the FGFR2 mutations and the clinical complications, we examined the FGFR2 gene in a patient with Apert syndrome associated with humeroradial synostosis, and found that the mutation was S252W. This report suggested that S252W mutation in FGFR2 may cause humeroradial synostosis in Apert syndrome.

Distinct craniofacial-skeletal-dermatological dysplasia in a patient with W290C mutation in FGFR2

Mutations in the fibroblast growth factor receptor genes (FGFR) have been known to be associated with many craniosynostosis syndromes with overlapping phenotypes. We studied a 15-year-old Thai boy with an unspecified craniosynostosis syndrome characterized by multiple suture craniosynostoses, a persistent anterior fontanel, corneal scleralization, choanal stenosis, atresia of the auditory meatus, broad thumbs and great toes, severe scoliosis, acanthosis nigricans, hydrocephalus, and mental retardation. Radiography revealed bony ankyloses of vertebral bodies of T9-12, humero-radio-ulnar joints, intercarpal joints, distal interphalangeal joints of fifth fingers, fibulo-tibial joints, intertarsal joints, and distal interphalangeal joints of the first toes. The patient was a heterozygous for a 870G --> T change resulting in a W290C amino acid substitution in the extracellular domain of the fibroblast growth factor receptor 2 gene (FGFR2). This mutation has previously been reported in a patient with severe Pfeiffer syndrome type 2 that is distinct from the craniosynostosis in our patient. These findings emphasize locus, allelic, and phenotypic heterogeneity of craniofacial-skeletal-dermatological syndrome due to FGFR2 mutations.

FGFs, their receptors, and human limb malformations: clinical and molecular correlations

Fibroblast growth factors (FGFs) comprise a family of 22 distinct proteins with pleiotropic signaling functions in development and homeostasis. These functions are mediated principally by four fibroblast growth factor receptors (FGFRs), members of the receptor tyrosine kinase family, with heparin glycosaminoglycan as an important cofactor. Developmental studies in chick and mouse highlight the critical role of FGF-receptor signaling in multiple phases of limb development, including the positioning of the limb buds, the maintenance of limb bud outgrowth, the detailed patterning of the limb elements, and the growth of the long bones. Corroborating these important roles, mutations of two members of the FGFR family (FGFR1 and FGFR2) are associated with human disorders of limb patterning; in addition, mutations of FGFR3 and FGF23 affect growth of the limb bones. Analysis of FGFR2 mutations in particular reveals a complex pattern of genotype/phenotype correlation, which will be reviewed in detail. Circumstantial evidence suggests that the more severe patterning abnormalities are mediated by illegitimate paracrine signaling in the mesoderm, mediated by FGF10 or by a related FGF, and this is beginning to gain some experimental support. A further test of this hypothesis is provided by a unique family segregating two FGFR2 mutations in cis (S252L; A315S), in which severe syndactyly occurs in the absence of the craniosynostosis that typically accompanies FGFR2 mutations.

Abnormal sterol metabolism in a patient with Antley-Bixler syndrome and ambiguous genitalia

Antley-Bixler syndrome (ABS) is a rare multiple anomaly syndrome comprising radiohumeral synostosis, bowed femora, fractures of the long bones, premature fusion of the calvarial sutures, severe midface hypoplasia, proptosis, choanal atresia, and, in some, ambiguous genitalia. Of fewer than 40 patients described to date, most have been sporadic, although reports of parental consanguinity and affected sibs of both sexes suggests autosomal recessive inheritance in some families. Known genetic causes among sporadic cases of ABS or ABS-like syndromes are missense mutations in the IgII and IgIII regions of FGFR2, although the assignment of the diagnosis of ABS to such children has been disputed. A third cause of an ABS-like phenotype is early in utero exposure to fluconazole, an inhibitor of lanosterol 14-alpha-demethylase. The fourth proposed cause of ABS is digenic inheritance combining heterozygosity or homozygosity for steroid 21-hydroxylase deficiency with effects from a second gene at an unknown locus. Because fluconazole is a strong inhibitor of lanosterol 14-alpha-demethylase (CYP51), we evaluated sterol metabolism in lymphoblast cell lines from an ABS patient without a known FGFR2 mutation and from a patient with an FGFR2 mutation and ABS-like manifestations. When grown in the absence of cholesterol to stimulate cholesterol biosynthesis, the cells from the ABS patient with ambiguous genitalia but without an FGFR2 mutation accumulated markedly increased levels of lanosterol and dihydrolanosterol. Although the abnormal sterol profile suggested a deficiency of lanosterol 14-alpha-demethylase, mutational analysis of its gene, CYP51, disclosed no obvious pathogenic mutation in any of its 10 exons or exon-intron boundaries. Sterol metabolism in lymphoblasts from the phenotypically unaffected mother was normal. Our results suggest that ABS can occur in a patient with an intrinsic defect of cholesterol biosynthesis at the level of lanosterol 14-alpha-demethylase, although the genetic nature of the deficiency remains to be determined.

Mutation analysis of Crouzon syndrome and identification of one novel mutation in Taiwanese patients

BACKGROUND

Crouzon syndrome is an autosomal dominant disorder causing premature fusion of the cranial suture. Mutations have been reported in exon IIIa or IIIc of the fibroblast growth factor receptor 2 (FGFR2) gene.

METHODS

In the present study, nine unrelated Crouzon syndrome patients were screened for mutations in the two exons of FGFR2 by polymerase chain reaction and direct sequencing.

RESULTS

Mutations were detected in 67% (6/9) of all cases. More than half the studied Crouzon patients carried a mutation resulting in either the loss or gain of a cysteine residue. A novel mutation, Tyr281Cys substitution, was discovered at exon IIIa.

CONCLUSIONS

The mechanisms by which the same genotypes cause different phenotypes for each type of craniosynostosis syndrome in still uncertain. However, the molecular identification of the FGFR gene has made a great impact on the clinical classification of craniosynostosis syndromes; a new classification based on genotypes seems to be unavoidable.

Antley-Bixler syndrome, description of two new cases and review of the literature

OBJECTIVE

Antley-Bixler syndrome (ABS) is a rare disorder characterized by multiple malformations of cartilage and bone including multisynostotic osteodysgenesis, midface hypoplasia, choanal atresia or stenosis, femoral bowing, neonatal fractures and multiple joint contractures and, occasionally, urogenital, gastrointestinal or cardiac defects. Since the first report in 1975, at least 34 cases (including this report) have been described. We present 2 cases of congenital hydrocephalus, suggesting the cause of craniosynostosis and midface hypoplasia is associated with ABS.

CLINICAL PRESENTATION

The first case was a 1-day-old female with Arnold-Chiari malformation, multiple cranial synostosis, obstructive hydrocephalus and radioulnahumeral synostosis. Ventriculoperitoneal (V-P) shunting was performed when she was 7 days old. She died 42 days later due to cardiopulmonary failure. The second case was a 2-month-old female with bilateral coronal synostosis, obstructive hydrocephalus and brachycephaly. V-P shunting was done soon after her admission, and bilateral lateral canthal advancement with the floating forehead procedure was performed 1 month later. She is still alive with good development.

DISCUSSION

The main anomalies of the ABS can be divided into 4 categories: craniofacial, skeletal, extremity and urogenital anomalies. They may be the result of mutation in the fibroblast growth factor receptor 2 (Ser351Cys) gene, which was confirmed in our case 2. Craniosynostosis combined with hydrocephalus created congenital increased intracranial pressure (IICP). Early V-P shunt implantation and surgical release of the closed suture and lateral canthal advancement should be done as soon as possible, ideally when the patient is younger than 3 months.

CONCLUSION

Early correction of craniosynostosis was feasible and safe for one of our patients. We offer our experience in the treatment of hydrocephalus and correction of craniosynostosis to relieve IICP.

The molecular control of upper extremity development: implications for congenital hand anomalies

As the molecular aspects of limb development are being unraveled, more of the congenital anomalies seen by hand surgeons in the clinical setting will have an identifiable molecular basis. The majority of the data available regarding the molecular development of the upper extremity have come from experimental animal studies, specifically the mouse and chicken. These findings are being discovered by either direct surgical and molecular manipulation of the developing limb or by production of mice deficient in specific genes. Relatively few specific human mutations that cause limb abnormalities have been identified. Hand surgeons should be aware of the basic molecular pathways controlling limb development because they are in a unique position to be able to identify patients with such deformities. In turn, detailed clinical descriptions of congenital anomalies affecting the upper extremity will advance the understanding of the cellular events controlled by the molecular pathways of limb development. This review describes the general molecular basis of limb development and correlates it with disease processes affecting the upper extremity.

The molecular and genetic basis of fibroblast growth factor receptor 3 disorders: the achondroplasia family of skeletal dysplasias, Muenke craniosynostosis, and Crouzon syndrome with acanthosis nigricans

Achondroplasia, the most common form of short-limbed dwarfism in humans, occurs between 1 in 15,000 and 40,000 live births. More than 90% of cases are sporadic and there is, on average, an increased paternal age at the time of conception of affected individuals. More then 97% of persons with achondroplasia have a Gly380Arg mutation in the transmembrane domain of the fibroblast growth factor receptor (FGFR) 3 gene. Mutations in the FGFR3 gene also result in hypochondroplasia, the lethal thanatophoric dysplasias, the recently described SADDAN (severe achondroplasia with developmental delay and acanthosis nigricans) dysplasia, and two craniosynostosis disorders: Muenke coronal craniosynostosis and Crouzon syndrome with acanthosis nigricans. Recent evidence suggests that the phenotypic differences may be due to specific alleles with varying degrees of ligand-independent activation, allowing the receptor to be constitutively active. Since the Gly380Arg achondroplasia mutation was recognized, similar observations regarding the conserved nature of FGFR mutations and resulting phenotype have been made regarding other skeletal phenotypes, including hypochondroplasia, thanatophoric dysplasia, and Muenke coronal craniosynostosis. These specific genotype-phenotype correlations in the FGFR disorders seem to be unprecedented in the study of human disease. The explanation for this high degree of mutability at specific bases remains an intriguing question.

Evidence for digenic inheritance in some cases of Antley-Bixler syndrome?

The Antley-Bixler syndrome has been thought to be caused by an autosomal recessive gene. However, patients with this phenotype have been reported with a new dominant mutation at the FGFR2 locus as well as in the offspring of mothers taking the antifungal agent fluconazole during early pregnancy. In addition to the craniosynostosis and joint ankylosis which are the clinical hallmarks of the condition, many patients, especially females, have genital abnormalities. We now report abnormalities of steroid biogenesis in seven of 16 patients with an Antley-Bixler phenotype. Additionally, we identify FGFR2 mutations in seven of these 16 patients, including one patient with abnormal steroidogenesis. These findings, suggesting that some cases of Antley-Bixler syndrome are the outcome of two distinct genetic events, allow a hypothesis to be formulated under which we may explain all the differing and seemingly contradictory circumstances in which the Antley-Bixler phenotype has been recognised.