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Biomedical subjects

A O Wilkie

Publications and source records attributed to A O Wilkie.

At least 19 recordsLinked to original sources
PubMed2001

Linkage of otopalatodigital syndrome type 2 (OPD2) to distal Xq28: evidence for allelism with OPD1.

Otopalatodigital syndrome type 1 (OPD1) is an X-linked semidominant condition characterized by malformations of the skeleton, auditory apparatus, and palate. Previous studies have established linkage to a 16-cM region of Xq27-q28. A proposed allelic variant of OPD1, termed "OPD2," is associated with a more severe, frequently lethal phenotype with visceral and brain anomalies in addition to skeletal, auditory, and palatal defects. We report linkage of the OPD2 phenotype to a 2-cM region of distal Xq28 in a Maori kindred, with a maximum multipoint LOD score of 3.31 between the markers DXS1073 and DXS1108. This provides support for allelism between OPD1 and OPD2 and reduces the size of the disease interval to 1.8-2.1 Mb. We also demonstrate that female carriers of this disorder exhibit skewed inactivation that segregates with the high-risk haplotype and may be inversely related to the severity with which they manifest features of the disorder.

Abnormalities, Multiple↗
PubMed2001

Craniosynostosis and related limb anomalies.

Many genetically determined craniosynostosis syndromes feature limb anomalies, implying that pathways of cranial suture and limb morphogenesis share some identical components. Identification of heterozygous mutations in FGFR1, FGFR2, FGFR3, TWIST and MSX2 in craniosynostosis has focused particular attention on these genes. Here we explore two themes: use of clinical/molecular analysis to provide new clues to pathophysiology and the contrasting effects of loss- and gain-of-function mutations. Apert syndrome is a severe craniosynostosis/syndactyly disorder usually caused by specific substitutions (Ser252Trp or Pro253Arg) in FGFR2. The relative severity of cranial and limb malformations varies in opposite directions for the two mutations, suggesting that these phenotypes arise by different mechanisms. Clinical and biochemical evidence supports a model in which alternative splice forms of FGFR2 mediate these distinct effects. Pro-->Arg substitutions equivalent the Pro253Arg/FGFR2 mutation occur in both FGFR1 and FGFR3, and are also associated with craniosynostosis. This suggests a common pathological mechanism, whereby enhanced affinity for a limited repertoire of tissue-specific ligand(s) excessively prolongs signalling in the cranial suture. The first MSX2 mutation in craniosynostosis was described in 1993 but this remains the only example. We have recently identified three MSX2 mutations associated with a different cranial phenotype, parietal foramina. DNA binding studies show that the craniosynostosis and parietal foramina arise from gain and loss of function, respectively.

Acrocephalosyndactylia↗
PubMed2001

A survey of TWIST for mutations in craniosynostosis reveals a variable length polyglycine tract in asymptomatic individuals.

The human TWIST gene encodes a 202 amino acid transcription factor characterized by a highly conserved basic-helix-loop-helix motif in the C-terminal half, and a less conserved N-terminal half that has binding activity toward the histone acetyltransferase p300. Between these domains is a repeat region of unknown function that encodes the glycine-rich sequence (Gly)5Ala(Gly)5. Heterozygous mutations of TWIST were previously described in Saethre-Chotzen craniosynostosis syndrome [El Ghouzzi et al., 1997; Howard et al., 1997]. During a search for TWIST mutations in patients with craniosynostosis, we identified, in addition to 11 novel and one previously described bona fide mutations, several individuals with rearrangements of the glycine-rich region, involving either deletion of 18 nucleotides or insertion of three, 15, or 21 nucleotides. None of these rearrangements was consistently associated with clinical disease and we conclude that they are at most weakly pathogenic. The glycine stretch may serve as a flexible linker between the functional domains of the TWIST protein, and as such may be subject to reduced evolutionary constraint.

Amino Acid Sequence↗
PubMed2001

Genetics of craniofacial development and malformation.

The head is anatomically the most sophisticated part of the body and its evolution was fundamental to the origin of vertebrates; understanding its development is a formidable problem in biology. A synthesis of embryology, evolution and mouse genetics is shaping our understanding of head development and in this review we discuss its application to studies of human craniofacial malformations. Many of these disorders have their origins in specific embryological processes, including abnormalities of brain patterning, of the migration and fusion of tissues in the face, and of bone differentiation in the skull vault.

Animals↗
PubMed2001

Haploinsufficiency of the human homeobox gene ALX4 causes skull ossification defects.

Inherited defects of skull ossification often manifest as symmetric parietal foramina (PFM; MIM 168500). We previously identified mutations of MSX2 in non-syndromic PFM and demonstrated genetic heterogeneity. Deletions of 11p11-p12 (proximal 11p deletion syndrome, P11pDS; MIM 601224) are characterized by multiple exostoses, attributable to haploinsufficiency of EXT2 and PFM. Here we identify ALX4, which encodes a paired-related homeodomain transcription factor, as the PFM disease gene in P11pDS.

Animals↗
PubMed2001

Mutational analysis in X-linked spondyloepiphyseal dysplasia tarda.

Spondyloepiphyseal dysplasia tarda (SEDT) is an X-linked recessive disorder characterized by short stature due to defective growth of the vertebral bodies. In addition, deformities of the femoral heads result in early onset secondary osteoarthritis of the hips. The disorder affects males only with heterozygous female carriers showing no consistent abnormalities. The gene causing SEDT, which is located on Xp22.12-p22.31, consists of 6 exons of which only exons 3, 4, 5, and 6 are translated to yield an 140 amino acid protein, referred to as SEDLIN. SEDLIN mutations have been observed in SEDT patients, and we have undertaken studies to characterize such mutations in four unrelated SEDT kindreds by DNA sequence analysis. We identified two nonsense and two intragenic deletional frameshift mutations. The nonsense mutations occurred in exons 4 (TGG-->TGA, Trp70Stop) and 6 (CGA-->TGA, Arg122Stop). Both of the intragenic deletions, which were approximately 750 bp and 1300-1445 bp in size, involved intron 5 and part of exon 6 and resulted in frameshifts that lead to premature termination (Stop) signals. Thus, all four mutations are predicted to result in truncated proteins. The results of our study expand the spectrum of SEDLIN mutations associated with SEDT, and this will help to elucidate further the role of this novel protein in the etiology of this form of osteochondrodysplasia.

Codon, Nonsense↗
PubMed2000

Newly recognised craniosynostosis syndrome that does not map to known disease loci.

We describe a consanguineous family of Pakistani origin with five sibs, three of whom were affected by craniosynostosis of variable presentation. In addition, they had other congenital abnormalities principally affecting neurological, ocular, and limb development. We provide linkage evidence using intragenic and flanking microsatellite markers suggesting that the disease in this family was not caused by a mutation in one of the known craniosynostosis loci (FGFR1, FGFR2, FGFR3, MSX2, TWIST). Given the clinical novelty and parental consanguinity, we hypothesise that the affected individuals were autozygous for a recessively inherited mutation, at a novel locus, predisposing to craniosynostosis.

Child↗
PubMed2000

Distinct mutations in the receptor tyrosine kinase gene ROR2 cause brachydactyly type B.

Brachydactyly type B (BDB) is an autosomal dominant skeletal disorder characterized by hypoplasia/aplasia of distal phalanges and nails. Recently, heterozygous mutations of the orphan receptor tyrosine kinase (TK) ROR2, located within a distinct segment directly after the TK domain, have been shown to be responsible for BDB. We report four novel mutations in ROR2 (two frameshifts, one splice mutation, and one nonsense mutation) in five families with BDB. The mutations predict truncation of the protein within two distinct regions immediately before and after the TK domain, resulting in a complete or partial loss of the intracellular portion of the protein. Patients affected with the distal mutations have a more severe phenotype than do those with the proximal mutation. Our analysis includes the first description of homozygous BDB in an individual with a 5-bp deletion proximal to the TK domain. His phenotype resembles an extreme form of brachydactyly, with extensive hypoplasia of the phalanges and metacarpals/metatarsals and absence of nails. In addition, he has vertebral anomalies, brachymelia of the arms, and a ventricular septal defect-features that are reminiscent of Robinow syndrome, which has also been shown to be caused by mutations in ROR2. The BDB phenotype, as well as the location and the nature of the BDB mutations, suggests a specific mutational effect that cannot be explained by simple haploinsufficiency and that is distinct from that in Robinow syndrome.

Amino Acid Sequence↗
PubMed2000

Expression patterns of Twist and Fgfr1, -2 and -3 in the developing mouse coronal suture suggest a key role for twist in suture initiation and biogenesis.

Sutural growth depends on maintenance of a balance between proliferation of osteogenic stem cells and their differentiation to form new bone, so that the stem cell population is maintained until growth of the skull is complete. The identification of heterozygous mutations in FGFR1, -2 and -3 and TWIST as well as microdeletions of TWIST in human craniosynostosis syndromes has highlighted these genes as playing important roles in maintaining the suture as a growth centre. In contrast to Drosophila, a molecular relationship between human (or other vertebrate) TWIST and FGFR genes has not yet been established. TWIST mutations exert their effect via haploinsufficiency whereas FGFR mutations have a gain-of-function mechanism of action. To investigate the biological basis of FGFR signalling pathways in the developing calvarium we compared the expression patterns of Twist with those of Fgfr1, -2 and -3 in the fetal mouse coronal suture over the course of embryonic days 14-18, as the suture is initiated and matures. Our results show that: (1) Twist expression precedes that of Fgfr genes at the time of initiation of the coronal suture; (2) in contrast to Fgfr transcripts, which are localised within and around the developing bone domains, Twist is expressed by the midsutural mesenchyme cells. Twist expression domains show some overlap with those of Fgfr2, which is expressed in the most immature (proliferating) osteogenic tissue.

Animals↗
PubMed2000

Dominant mutations in ROR2, encoding an orphan receptor tyrosine kinase, cause brachydactyly type B.

Inherited limb malformations provide a valuable resource for the identification of genes involved in limb development. Brachydactyly type B (BDB), an autosomal dominant disorder, is the most severe of the brachydactylies and characterized by terminal deficiency of the fingers and toes. In the typical form of BDB, the thumbs and big toes are spared, sometimes with broadening or partial duplication. The BDB1 locus was previously mapped to chromosome 9q22 within an interval of 7.5 cM (refs 9,10). Here we describe mutations in ROR2, which encodes the orphan receptor tyrosine kinase ROR2 (ref. 11), in three unrelated families with BDB1. We identified distinct heterozygous mutations (2 nonsense, 1 frameshift) within a 7-amino-acid segment of the 943-amino-acid protein, all of which predict truncation of the intracellular portion of the protein immediately after the tyrosine kinase domain. The localized nature of these mutations suggests that they confer a specific gain of function. We obtained further evidence for this by demonstrating that two patients heterozygous for 9q22 deletions including ROR2 do not exhibit BDB. Expression of the mouse mouse orthologue, Ror2, early in limb development indicates that BDB arises as a primary defect of skeletal patterning.

Amino Acid Sequence↗
PubMed2000

Functional haploinsufficiency of the human homeobox gene MSX2 causes defects in skull ossification.

The genetic analysis of congenital skull malformations provides insight into normal mechanisms of calvarial osteogenesis. Enlarged parietal foramina (PFM) are oval defects of the parietal bones caused by deficient ossification around the parietal notch, which is normally obliterated during the fifth fetal month. PFM are usually asymptomatic, but may be associated with headache, scalp defects and structural or vascular malformations of the brain. Inheritance is frequently autosomal dominant, but no causative mutations have been identified in non-syndromic cases. We describe here heterozygous mutations of the homeobox gene MSX2 (located on 5q34-q35) in three unrelated families with PFM. One is a deletion of approximately 206 kb including the entire gene and the others are intragenic mutations of the DNA-binding homeodomain (RK159-160del and R172H) that predict disruption of critical intramolecular and DNA contacts. Mouse Msx2 protein with either of the homeodomain mutations exhibited more than 85% reduction in binding to an optimal Msx2 DNA-binding site. Our findings contrast with the only described MSX2 homeodomain mutation (P148H), associated with craniosynostosis, that binds with enhanced affinity to the same target. This demonstrates that MSX2 dosage is critical for human skull development and suggests that PFM and craniosynostosis result, respectively, from loss and gain of activity in an MSX2-mediated pathway of calvarial osteogenic differentiation.

Adult↗
PubMed2000

Recessive Robinow syndrome, allelic to dominant brachydactyly type B, is caused by mutation of ROR2.

The autosomal recessive form of Robinow syndrome (RRS; MIM 268310) is a severe skeletal dysplasia with generalized limb bone shortening, segmental defects of the spine, brachydactyly and a dysmorphic facial appearance. We previously mapped the gene mutated in RRS to chromosome 9q22 (ref. 4), a region that overlaps the locus for autosomal dominant brachydactyly type B (refs 5,6). The recent identification of ROR2, encoding an orphan receptor tyrosine kinase, as the gene mutated in brachydactyly type B (BDB1; ref. 7) and the mesomelic dwarfing in mice homozygous for a lacZ and/or a neo insertion into Ror2 (refs 8,9) made this gene a candidate for RRS. Here we report homozygous missense mutations in both intracellular and extracellular domains of ROR2 in affected individuals from 3 unrelated consanguineous families, and a nonsense mutation that removes the tyrosine kinase domain and all subsequent 3' regions of the gene in 14 patients from 7 families from Oman. The nature of these mutations suggests that RRS is caused by loss of ROR2 activity. The identification of mutations in three distinct domains (containing Frizzled-like, kringle and tyrosine kinase motifs) indicates that these are all essential for ROR2 function.

Abnormalities, Multiple↗
PubMed2000

A novel mutation, Ala315Ser, in FGFR2: a gene-environment interaction leading to craniosynostosis?

Mutations in the fibroblast growth factor receptor 1, 2 and 3 (FGFR1, -2 and -3) and TWIST genes have been identified in several syndromic forms of craniosynostosis. There remains, however, a significant number of patients with non-syndromic craniosynostosis in whom no genetic cause can be identified. We describe a novel heterozygous mutation of FGFR2 (943G --> T, encoding the amino acid substitution Ala315Ser) in a girl with non-syndromic unicoronal craniosynostosis. The mutation is also present in her mother and her maternal grandfather who have mild facial asymmetry but do not have craniosynostosis. None of these individuals has the Crouzonoid appearance typically associated with FGFR2 mutations. However, the obstetric history revealed that the proband was in persistent breech presentation in utero and was delivered by Caesarean section, at which time compression of the skull was apparent. We propose that this particular FGFR2 mutation only confers a predisposition to craniosynostosis and that an additional environmental insult (in this case foetal head constraint associated with breech position) is necessary for craniosynostosis to occur. To our knowledge, this is the first report of an interaction between a weakly pathogenic mutation and intrauterine constraint, leading to craniosynostosis.

Alanine↗
PubMed2000

Paternal origin of FGFR2 mutations in sporadic cases of Crouzon syndrome and Pfeiffer syndrome.

Crouzon syndrome and Pfeiffer syndrome are both autosomal dominant craniosynostotic disorders that can be caused by mutations in the fibroblast growth factor receptor 2 (FGFR2) gene. To determine the parental origin of these FGFR2 mutations, the amplification refractory mutation system (ARMS) was used. ARMS PCR primers were developed to recognize polymorphisms that could distinguish maternal and paternal alleles. A total of 4,374 bases between introns IIIa and 11 of the FGFR2 gene were sequenced and were assayed by heteroduplex analysis, to identify polymorphisms. Two polymorphisms (1333TA/TATA and 2710 C/T) were found and were used with two previously described polymorphisms, to screen a total of 41 families. Twenty-two of these families were shown to be informative (11 for Crouzon syndrome and 11 for Pfeiffer syndrome). Eleven different mutations in the 22 families were detected by either restriction digest or allele-specific oligonucleotide hybridization of ARMS PCR products. We molecularly proved the origin of these different mutations to be paternal for all informative cases analyzed (P=2. 4x10-7; 95% confidence limits 87%-100%). Advanced paternal age was noted for the fathers of patients with Crouzon syndrome or Pfeiffer syndrome, compared with the fathers of control individuals (34. 50+/-7.65 years vs. 30.45+/-1.28 years, P<.01). Our data on advanced paternal age corroborates and extends previous clinical evidence based on statistical analyses as well as additional reports of advanced paternal age associated with paternal origin of three sporadic mutations causing Apert syndrome (FGFR2) and achondroplasia (FGFR3). Our results suggest that older men either have accumulated or are more susceptible to a variety of germline mutations.

Acrocephalosyndactylia↗
PubMed2000

Potential gene conversion and source genes for recently integrated Alu elements.

Alu elements comprise >10% of the human genome. We have used a computational biology approach to analyze the human genomic DNA sequence databases to determine the impact of gene conversion on the sequence diversity of recently integrated Alu elements and to identify Alu elements that were potentially retroposition competent. We analyzed 269 Alu Ya5 elements and identified 23 members of a new Alu subfamily termed Ya5a2 with an estimated copy number of 35 members, including the de novo Alu insertion in the NF1 gene. Our analysis of Alu elements containing one to four (Ya1-Ya4) of the Ya5 subfamily-specific mutations suggests that gene conversion contributed as much as 10%-20% of the variation between recently integrated Alu elements. In addition, analysis of the middle A-rich region of the different Alu Ya5 members indicates a tendency toward expansion of this region and subsequent generation of simple sequence repeats. Mining the databases for putative retroposition-competent elements that share 100% nucleotide identity to the previously reported de novo Alu insertions linked to human diseases resulted in the retrieval of 13 exact matches to the NF1 Alu repeat, three to the Alu element in BRCA2, and one to the Alu element in FGFR2 (Apert syndrome). Transient transfections of the potential source gene for the Apert's Alu with its endogenous flanking genomic sequences demonstrated the transcriptional and presumptive transpositional competency of the element.

Alleles↗
PubMed1999

Characterisation of the human snail (SNAI1) gene and exclusion as a major disease gene in craniosynostosis.

The Snail family of proteins in vertebrates comprises two zinc-finger transcription factors, Snail and Slug, which are thought to be involved in the formation of the mesoderm and neural crest. Here, we describe the isolation and characterisation of the human Snail (SNAI1) gene and a related Snail-like pseudogene, SNAI1P. SNAI1 spans approximately 6.4kb, contains three exons and has a CpG island upstream of the coding sequence. A single transcript of 1.9 kb was detected in several human foetal tissues, with the highest expression in the kidney. The SNAI1 open reading frame encodes a protein of 264 amino acids containing four zinc-finger motifs that show 87.1% identity to mouse Snail (mSna). SNAI1 was mapped to chromosome band 20q13.1 and is likely to lie between markers D20S109 and D20S196. Investigation of SNAI1 coding sequences by single-strand conformation polymorphism analysis excluded SNAI1 as a major disease gene in craniosynostosis. Two single nucleotide polymorphisms encoding synonymous amino acids were identified in exon 2. The SNAI1P pseudogene was isolated, sequenced and mapped to chromosome band 2q34.

Amino Acid Sequence↗