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PubMed2000

Loss of fibroblast growth factor receptor 2 ligand-binding specificity in Apert syndrome.

Craniosynostosis syndromes are autosomal dominant human skeletal diseases that result from various mutations in fibroblast growth factor receptor genes (Fgfrs). Apert syndrome (AS) is one of the most severe craniosynostosis syndromes and is associated with severe syndactyly of the hands and feet and with central nervous system malformations. AS is caused by specific missense mutations in one of two adjacent amino acid residues (S252W or P253R) in the highly conserved region linking Ig-like domains II and III of FGFR2. Here we demonstrate that these mutations break one of the cardinal rules governing ligand specificity of FGFR2. We show that the S252W mutation allows the mesenchymal splice form of FGFR2 (FGFR2c) to bind and to be activated by the mesenchymally expressed ligands FGF7 or FGF10 and the epithelial splice form of FGFR2 (FGFR2b) to be activated by FGF2, FGF6, and FGF9. These data demonstrate loss of ligand specificity of FGFR2 with retained ligand dependence for receptor activation. These data suggest that the severe phenotypes of AS likely result from ectopic ligand-dependent activation of FGFR2.

3T3 Cells↗
PubMed2001

Absence of post-translational aspartyl beta-hydroxylation of epidermal growth factor domains in mice leads to developmental defects and an increased incidence of intestinal neoplasia.

The BAH genomic locus encodes three distinct proteins: junctin, humbug, and BAH. All three proteins share common exons, but differ significantly based upon the use of alternative terminal exons. The biological roles of BAH and humbug and their functional relationship to junctin remain unclear. To evaluate the role of BAH in vivo, the catalytic domain of BAH was specifically targeted such that the coding regions of junctin and humbug remained undisturbed. BAH null mice lack measurable BAH protein in several tissues, lack aspartyl beta-hydroxylase activity in liver preparations, and exhibit no hydroxylation of the epidermal growth factor (EGF) domain of clotting Factor X. In addition to reduced fertility in females, BAH null mice display several developmental defects including syndactyly, facial dysmorphology, and a mild defect in hard palate formation. The developmental defects present in BAH null mice are similar to defects observed in knock-outs and hypomorphs of the Notch ligand Serrate-2. In this work, beta-hydroxylation of Asp residues in EGF domains is demonstrated for a soluble form of a Notch ligand, human Jagged-1. These results along with recent reports that another post-translational modification of EGF domains in Notch gene family members (glycosylation by Fringe) alters Notch pathway signaling, lends credence to the suggestion that aspartyl beta-hydroxylation may represent another post-translational modification of EGF domains that can modulate Notch pathway signaling. Previous work has demonstrated increased levels of BAH in certain tumor tissues and a role for BAH in tumorigenesis has been proposed. The role of hydroxylase in tumor formation was tested directly by crossing BAH KO mice with an intestinal tumor model, APCmin mice. Surprisingly, BAH null/APCmin mice show a statistically significant increase in both intestinal polyp size and number when compared with BAH wild-type/APCmin controls. These results suggest that, in contrast to expectations, loss of BAH catalytic activity may promote tumor formation.

Amino Acid Sequence↗
PubMed2004

A soluble form of fibroblast growth factor receptor 2 (FGFR2) with S252W mutation acts as an efficient inhibitor for the enhanced osteoblastic differentiation caused by FGFR2 activation in Apert syndrome.

Apert syndrome is an autosomal dominant disease characterized by craniosynostosis and bony syndactyly associated with point mutations (S252W and P253R) in the fibroblast growth factor receptor (FGFR) 2 that cause FGFR2 activation. Here we investigated the role of the S252W mutation of FGFR2 on osteoblastic differentiation. Osteoblastic cells derived from digital bone in two Apert patients with the S252W mutation showed more prominent alkaline phosphatase activity, osteocalcin and osteopontin mRNA expression, and mineralized nodule formation compared with the control osteoblastic cells derived from two independent non-syndromic polydactyly patients. Stable clones of the human MG63 osteosarcoma cells (MG63-Ap and MG63-IIIc) overexpressing a splice variant form of FGFR2 with or without the S252W mutation (FGFR2IIIcS252W and FGFR2IIIc) showed a higher RUNX2 mRNA expression than parental MG63 cells. Furthermore MG63-Ap exhibited a higher osteopontin mRNA expression than did MG63-IIIc. The enhanced osteoblastic marker gene expression and mineralized nodule formation of the MG63-Ap was inhibited by the conditioned medium from the COS-1 cells overexpressing the soluble FGFR2IIIcS252W. Furthermore the FGF2-induced osteogenic response in the mouse calvarial organ culture system was blocked by the soluble FGFR2IIIcS252W. These results show that the S252W mutation in the FGFR2 gene enhances the osteoblast phenotype in human osteoblasts and that a soluble FGFR2 with the S252W mutation controls osteoblast differentiation induced by the S252W mutation through a dominant negative effect on FGFR2 signaling in Apert syndrome.

Acrocephalosyndactylia↗
PubMed2007

Elucidation, quantitative refinement, and in vivo utilization of the HOXA13 DNA binding site.

Mutations in Hoxa13 cause malformations of the appendicular skeleton and genitourinary tract, including digit loss, syndactyly, and hypospadias. To determine the molecular basis for these defects, the DNA sequences bound by HOXA13 were empirically determined, revealing a novel high affinity binding site. Correlating the utilization of this high affinity binding site with genes exhibiting perturbed expression in Hoxa13 mutant limbs, we identified that HOXA13 suppresses the expression of the BMP antagonist, Sostdc1. In the absence of HOXA13 function, Sostdc1 is ectopically expressed in the distal limb, causing reduced expression of BMP-activated genes and decreased SMAD phosphorylation. Limb chromatin immunoprecipitation revealed HOXA13 binding at its high affinity site in two conserved Sostdc1 regulatory sites in vivo. In vitro, HOXA13 represses gene expression through the Sostdc1 high affinity binding sites in a dosage-dependent manner. Together, these findings confirm that the high affinity HOXA13 binding site deduced by quantitative analyses is used in vivo to facilitate HOXA13 target gene regulation, providing a critical advance toward understanding the molecular basis for defects associated with the loss of HOXA13 function.

Adaptor Proteins, Signal Transducing↗
PubMed1997

Retinoic acid-induced abnormal development of hindlimb joints in the mouse.

Following a single oral dose of 200 mg/kg of retinoic acid (RA) to pregnant TO mice on day 12 of gestation, fetuses were collected on day 18. RA-treatment resulted in a modest increase in embryo resorption, a significant reduction in fetal body weight and a 96% incidence of limb malformations. Both fore- and hindlimbs were malformed in equal frequency. In this study, only the anomalies of the hindlimbs have been considered. Alizarin stained skeletal preparations revealed a reduction in both length and thickness as well as bowing of the long bones. Agenesis of most of the metatarsals and some toes and/or phalanges was also noted. Paraffin sections cut serially confirmed the gross observations. Additionally, the joint cavities were found to be absent and the cartilaginous ends of the articulating bones were continuous with each other. In some this union was partial and occasionally the joint was only represented by a fine slit. The synovial membrane and other intra-articular structures were either rudimentary or absent. There was a marked reduction in endochondral ossification. Bony union in syndactyly was occasionally observed. These data indicate that a high dose of RA, both inhibits skeletal growth and interferes with the differentiation of the inter-zone mesenchyme, thus resulting in abnormalities of the joints in the TO mouse fetuses.

Animals↗
PubMed2002

Correction of a deformed thumb by distraction of the phalanx.

We used distraction osteogenesis to correct six deformed thumbs in four patients ranging in age from 4 to 7 years. Two of the patients had Apert syndrome (syndromic craniosynostosis with symmetrical syndactyly) and two had polydactyly. We used a small fixator with a ball joint and successfully corrected the angular deformity after lengthening the proximal phalanx by distraction. This single inclusive procedure was extremely useful. We found the optimal distraction regimen for the digital phalanx was a one day waiting period and lengthening at 1 mm/day. The mean healing indexes were 37.2 days/cm (range 24.2 to 41.5) in those with Apert syndrome and 64.3 days/cm in those with polydactyly (62.5 and 66.0). Our results suggest that osteogenesis at the distraction site may be quicker in patients with Apert syndrome than in those with polydactyly.

Acrocephalosyndactylia↗
PubMed2005

Bilateral complete isolated cryptophthalmos: a case report.

Cryptophthalmos is a condition of congenital eyelid malformation most commonly accompanied by syndactyly, urogenital anomalies, and cognitive impairments as in Fraser syndrome. We report on a patient with characteristic features consistent with autosomal dominant bilateral complete isolated cryptophthalmos. This patient represents only the sixth documented case of bilateral complete isolated cryptophthalmos. Defining characteristics of this variety are discussed, including bilateral central dimpling over the globes, normal eyebrow growth, and the absence of cognitive impairment. We introduce phenotypic features that distinguish bilateral isolated cryptophthalmos from other forms and discuss its relatively favorable prognosis.

Abnormalities, Multiple↗
PubMed1984

Ethylenethiourea-induced hindpaw deformities in mice and effects of metabolic modifiers on their occurrence.

Time-mated Swiss-Webster mice were pretreated in separate experiments with phenobarbital (60 mg/kg X d sc on d 7-10 of pregnancy), SKF-525A (40 mg/kg ip on d 12 of pregnancy) or 3-methylcholanthrene (20 mg/kg X d on d 10-12 of pregnancy). On the d 12 of pregnancy (1 h after SKF-525A or 3-methylcholanthrene treatment), one group each of pretreated mice was given a single oral dose of 1600, 2000, or 2400 mg/kg of ethylenethiourea (ETU) as a 5% concentrate in a 1.5% aqueous gelatin solution, which as a vehicle was given to other pretreated groups. The respective volume doses were 3.2, 4.0, or 4.8 ml/100 g body weight with the controls given 4.8 ml/100 g body weight of vehicle alone. Maternal toxicity was observed in all groups given ETU, whether pretreated with metabolic modifiers or not. In the three experiments, treatment with ETU alone reduced fetal weight by 15% at 2400 mg/kg and 8% with the remaining 2 doses, and increased the incidence of resorptions (19-62% with the 2400 mg/kg dose, 8-59% at 2000 mg/kg, and 7-32% at the 1600 mg/kg dose). The significant defects with incidence ranges in three experiments were: hindpaw ectrodactyly, 2-6% at 1600 mg/kg, 4-20% at 2000, and 20-29% at 2400 mg/kg; and hindpaw syndactyle, 3% at 16 mg/kg, 6-14% at 2000, and 2-12% at 2400 mg/kg doses. Minor incidences of cleft palate and hindpaw polydactyly were also observed. Phenobarbital pretreatment did not change the ETU-induced maternal or fetal effects. SKF-525A enhanced the resorptions and reduced the litter-size but had no effect on fetal malformations. The 3-methylcholanthrene pretreatment reduced the ETU-induced incidences of hindpaw ectrodactyly, hindpaw syndactyly, and cleft palate at the 2000 and 2400 mg/kg doses. Previous studies with rats and hamsters revealed that SKF-525A enhanced the ETU-induced fetal malformations but phenobarbital and 3-methyl-cholanthrene had no effect in these two species.

Abnormalities, Drug-Induced↗
PubMed1998

Linkage disequilibrium mapping of the gene for Margarita Island ectodermal dysplasia (ED4) to 11q23.

Margarita Island ectodermal dysplasia (ED4) is an autosomal recessive disorder characterized by unusual facies, dental anomalies, hypotrichosis, palmoplantar hyperkeratosis and onychodysplasia, syndactyly, and cleft lip/cleft palate. We have used an affected-only DNA-pooling strategy to carry out linkage disequilibrium mapping of the ED4 gene to 11q23. Haplotype analysis of four complex Margarita Island ED4 families localized the ED4 gene to an approximately 1-2-Mb interval spanned by just two YACs.

Chromosome Mapping↗
PubMed1999

Monodactylous limbs and abnormal genitalia are associated with hemizygosity for the human 2q31 region that includes the HOXD cluster.

Vertebrates have four clusters of Hox genes (HoxA, HoxB, HoxC, and HoxD). A variety of expression and mutation studies indicate that posterior members of the HoxA and HoxD clusters play an important role in vertebrate limb development. In humans, mutations in HOXD13 have been associated with type II syndactyly or synpolydactyly, and, in HOXA13, with hand-foot-genital syndrome. We have investigated two unrelated children with a previously unreported pattern of severe developmental defects on the anterior-posterior (a-p) limb axis and in the genitalia, consisting of a single bone in the zeugopod, either monodactyly or oligodactyly in the autopod of all four limbs, and penoscrotal hypoplasia. Both children are heterozygous for a deletion that eliminates at least eight (HOXD3-HOXD13) of the nine genes in the HOXD cluster. We propose that the patients' phenotypes are due in part to haploinsufficiency for HOXD-cluster genes. This hypothesis is supported by the expression patterns of these genes in early vertebrate embryos. However, the involvement of additional genes in the region could explain the discordance, in severity, between these human phenotypes and the milder, non-polarized phenotypes present in mice hemizygous for HoxD cluster genes. These cases represent the first reported examples of deficiencies for an entire Hox cluster in vertebrates and suggest that the diploid dose of human HOXD genes is crucial for normal growth and patterning of the limbs along the anterior-posterior axis.

Child, Preschool↗
PubMed2000

Split-hand/split-foot malformation is caused by mutations in the p63 gene on 3q27.

Split-hand/split-foot malformation (SHFM), a limb malformation involving the central rays of the autopod and presenting with syndactyly, median clefts of the hands and feet, and aplasia and/or hypoplasia of the phalanges, metacarpals, and metatarsals, is phenotypically analogous to the naturally occurring murine Dactylaplasia mutant (Dac). Results of recent studies have shown that, in heterozygous Dac embryos, the central segment of the apical ectodermal ridge (AER) degenerates, leaving the anterior and posterior segments intact; this finding suggests that localized failure of ridge maintenance activity is the fundamental developmental defect in Dac and, by inference, in SHFM. Results of gene-targeting studies have demonstrated that p63, a homologue of the cell-cycle regulator TP53, plays a critically important role in regulation of the formation and differentiation of the AER. Two missense mutations, 724A-->G, which predicts amino acid substitution K194E, and 982T-->C, which predicts amino acid substitution R280C, were identified in exons 5 and 7, respectively, of the p63 gene in two families with SHFM. Two additional mutations (279R-->H and 304R-->Q) were identified in families with EEC (ectrodactyly, ectodermal dysplasia, and facial cleft) syndrome. All four mutations are found in exons that fall within the DNA-binding domain of p63. The two amino acids mutated in the families with SHFM appear to be primarily involved in maintenance of the overall structure of the domain, in contrast to the p63 mutations responsible for EEC syndrome, which reside in amino acid residues that directly interact with the DNA.

Amino Acid Sequence↗
PubMed2002

KCNJ2 mutation results in Andersen syndrome with sex-specific cardiac and skeletal muscle phenotypes.

Evaluation of candidate loci culminated in the identification of a heterozygous missense mutation (R67W) in KCNJ2, the gene encoding the inward-rectifying potassium current, Kir2.1, in 41 members of a kindred in which ventricular arrhythmias (13 of 16 female members [81%]) and periodic paralysis (10 of 25 male members [40%]) segregated as autosomal dominant traits with sex-specific variable expressivity. Some mutation carriers exhibited dysmorphic features, including hypertelorism, small mandible, syndactyly, clinodactyly, cleft palate, and scoliosis, which, together with cardiodysrhythmic periodic paralysis, have been termed "Andersen syndrome." However, no individual exhibited all manifestations of Andersen syndrome, and this diagnosis was not considered in the proband until other family members were examined. Other features seen in this kindred included unilateral dysplastic kidney and cardiovascular malformation (i.e., bicuspid aortic valve, bicuspid aortic valve with coarctation of the aorta, or valvular pulmonary stenosis), which have not been previously associated. Nonspecific electrocardiographic abnormalities were identified in some individuals, but none had a prolonged QT interval. Biophysical characterization of R67W demonstrated loss of function and a dominant-negative effect on Kir2.1 current. These findings support the suggestion that, in addition to its recognized role in function of cardiac and skeletal muscle, KCNJ2 plays an important role in developmental signaling.

Abnormalities, Multiple↗
PubMed2002

Connexin 43 (GJA1) mutations cause the pleiotropic phenotype of oculodentodigital dysplasia.

Gap junctions are assemblies of intercellular channels that regulate a variety of physiologic and developmental processes through the exchange of small ions and signaling molecules. These channels consist of connexin family proteins that allow for diversity of channel composition and conductance properties. The human connexin 43 gene, or GJA1, is located at human chromosome 6q22-q23 within the candidate region for the oculodentodigital dysplasia locus. This autosomal dominant syndrome presents with craniofacial (ocular, nasal, and dental) and limb dysmorphisms, spastic paraplegia, and neurodegeneration. Syndactyly type III and conductive deafness can occur in some cases, and cardiac abnormalities are observed in rare instances. We found mutations in the GJA1 gene in all 17 families with oculodentodigital dysplasia that we screened. Sixteen different missense mutations and one codon duplication were detected. These mutations may cause misassembly of channels or alter channel conduction properties. Expression patterns and phenotypic features of gja1 animal mutants, reported elsewhere, are compatible with the pleiotropic clinical presentation of oculodentodigital dysplasia.

Adolescent↗
PubMed1995

A second autosomal split hand/split foot locus maps to chromosome 10q24-q25.

Ectrodactyly (split hand/split foot malformation, SHSF) is a human limb malformation characterized by absent central digital rays, deep median cleft, and syndactyly of remaining digits. The disorder is genetically heterogeneous, with at least two loci thus far determined: an autosomal locus at 7q21 designated SHFM1 and an X-linked locus at Xq26 designated SHFM2. Cytogenetic analysis of sporadic SHSF patients and linkage studies in extended pedigrees both suggest more than one autosomal locus exists. We report a novel SHSF locus suggested by a stillborn infant with ectrodactyly and other malformations who inherited an unbalanced translocation resulting in monosomy 4p15.1-4pter and trisomy for 10q25.2-qter. To investigate 10q25 as a possible split hand/split foot locus, microsatellite markers spanning 52 cM of 10q were utilized for linkage analysis of a large autosomal dominant SHSF pedigree in which the region encompassing SHFM1 previously was excluded as containing the causative mutation. The marker D10S583 was fully informative in the family, giving a maximum LOD score of 4.21 at recombination theta = 0.00. Recombination haplotypes define the 9 cM region between D10S541 and D10S574 as inclusive for this second autosomal SHSF locus, for which we propose the designation SHFM3.

Abnormalities, Multiple↗
PubMed1997

Translocation breakpoint maps 5 kb 3' from TWIST in a patient affected with Saethre-Chotzen syndrome.

Saethre-Chotzen syndrome, a common autosomal dominant craniosynostosis in humans, is characterized by brachydactyly, soft tissue syndactyly and facial dysmorphism including ptosis, facial asymmetry, and prominent ear crura. Previously, we identified a yeast artificial chromosome that encompassed the breakpoint of an apparently balanced t(6;7) (q16.2;p15.3) translocation associated with a mild form of Saethre-Chotzen syndrome. We now describe, at the DNA sequence level, the region on chromosome 7 affected by this translocation event. The rearrangement occurred approximately 5 kb 3' of the human TWIST locus and deleted 518 bp of chromosome 7. The TWIST gene codes for a transcription factor containing a basic helix-loop-helix (b-HLH) motif and has recently been described as a candidate gene for Saethre-Chotzen syndrome, based on the detection of mutations within the coding region. Potential exon sequences flanking the chromosome 7 translocation breakpoint did not hit known genes in database searches. The chromosome rearrangement downstream of TWIST is compatible with the notion that this is a Saethre-Chotzen syndrome gene and implies loss of function of one allele by a positional effect as a possible mechanism of mutation to evoke the syndrome.

Acrocephalosyndactylia↗
PubMed1998

Apert syndrome mutations in fibroblast growth factor receptor 2 exhibit increased affinity for FGF ligand.

Dominantly acting mutations of the fibroblast growth factor (FGF) receptor 2 (FGFR2) gene have been implicated in various craniosynostosis syndromes. Apert syndrome, characterized in addition by syndactyly of the limbs, involves specific mutations at two adjacent residues, Ser252Trp and Pro253Arg, predicted to lie in the linker region between IgII and IgIII of the FGFR2 ligand-binding domain. We have analysed the interaction of FGF ligands with wild-type and Apert-type mutant FGFR2 ectodomains in solution. Wild-type and Apert-type receptors form a complex with FGF ligands with a stoichiometry of 2:2 (ligand:receptor). The kinetics and specificity of ligand binding to wild-type and Apert mutant receptors have been analysed using surface plasmon resonance techniques. This reveals that Apert mutations, compared with wild-type, exhibit a selective decrease in the dissociation kinetics of FGF2, but not of other FGF ligands examined. In contrast, the substitution Ser252Leu in FGFR2, previously observed in several asymptomatic individuals, exhibited wild-type kinetics. These findings indicate that Apert syndrome arises as a result of increased affinity of mutant receptors for specific FGF ligands which leads to activation of signalling under conditions where availability of ligand is limiting.

Acrocephalosyndactylia↗
PubMed2003

Mutations at the mouse ichthyosis locus are within the lamin B receptor gene: a single gene model for human Pelger-Huët anomaly.

The nature of the wild-type gene product at the mouse ichthyosis (ic) locus has been of great interest because mutations at this locus cause marked abnormalities in nuclear heterochromatin, similar to those observed in Pelger-Huët anomaly (PHA). We recently found that human PHA is caused by mutations in the gene (LBR) encoding lamin B receptor, an evolutionarily conserved inner nuclear membrane protein involved in nuclear assembly and chromatin binding. Mice homozygous for deleterious alleles at the ichthyosis (ic) locus present with a blood phenotype similar to PHA, and develop other phenotypic abnormalities, including alopecia, variable expression of syndactyly and hydrocephalus. The ic locus on mouse chromosome 1 shares conserved synteny with the chromosomal location of the human LBR locus on human chromosome 1. In this study, we identified one nonsense (815ins) and two frameshift mutations (1088insCC and 1884insGGAA) within the Lbr gene of mice homozygous for either of three independent mutations (ic, ic(J) and ic(4J), respectively) at the ichthyosis locus. These allelic mutations are predicted to result in truncated or severely impaired LBR protein. Our studies of mice homozygous for the ic(J) mutation revealed a complete loss of LBR protein as shown by immunofluorescence microscopy and immunoblotting. The findings provide the molecular basis for the heterochromatin clumping and other distinct phenotypes caused by ic mutations. These spontaneous Lbr mutations confirm the molecular basis of human PHA and provide a small animal model for determination of the precise function of LBR in normal and pathological states.

Animals↗
PubMed2004

Biochemical analysis of pathogenic ligand-dependent FGFR2 mutations suggests distinct pathophysiological mechanisms for craniofacial and limb abnormalities.

Gain-of-function missense mutations in FGF receptor 2 (FGFR2) are responsible for a variety of craniosynostosis syndromes including Apert syndrome (AS), Pfeiffer syndrome (PS) and Crouzon syndrome (CS). Unlike the majority of FGFR2 mutations, S252W and P253R AS mutations and a D321A PS mutation retain ligand-dependency and are also associated with severe limb pathology. In addition, a recently identified ligand-dependent S252L/A315S double mutation in FGFR2 was shown to cause syndactyly in the absence of craniosynostosis. Here, we analyze the effect of the canonical AS mutations, the D321A PS mutation and the S252L/A315S double mutation on FGFR2 ligand binding affinity and specificity using surface plasmon resonance. Both AS mutations and the D321A PS mutation, but not the S252L/A315S double mutation, increase the binding affinity of FGFR2c to multiple FGFs expressed in the cranial suture. Additionally, all four pathogenic mutations also violate FGFR2c ligand binding specificity and enable this receptor to bind FGF10. Based on our data, we propose that an increase in mutant FGFR2c binding to multiple FGFs results in craniosynostosis, whereas binding of mutant FGFR2c to FGF10 results in severe limb pathology. Structural and biophysical analysis shows that AS mutations in FGFR2b also enhance and violate FGFR2b ligand binding affinity and specificity, respectively. We suggest that elevated AS mutant FGFR2b signaling may account for the dermatological manifestations of AS.

Craniofacial Abnormalities↗