Publications by authors named "Naomi L Baker"

13 Publications

  • Page 1 of 1

Monoallelic BMP2 Variants Predicted to Result in Haploinsufficiency Cause Craniofacial, Skeletal, and Cardiac Features Overlapping Those of 20p12 Deletions.

Am J Hum Genet 2017 Dec 30;101(6):985-994. Epub 2017 Nov 30.

Murdoch Children's Research Institute, Melbourne, VIC 3052, Australia; Department of Paediatrics, University of Melbourne, Melbourne, VIC 3052, Australia.

Bone morphogenetic protein 2 (BMP2) in chromosomal region 20p12 belongs to a gene superfamily encoding TGF-β-signaling proteins involved in bone and cartilage biology. Monoallelic deletions of 20p12 are variably associated with cleft palate, short stature, and developmental delay. Here, we report a cranioskeletal phenotype due to monoallelic truncating and frameshift BMP2 variants and deletions in 12 individuals from eight unrelated families that share features of short stature, a recognizable craniofacial gestalt, skeletal anomalies, and congenital heart disease. De novo occurrence and autosomal-dominant inheritance of variants, including paternal mosaicism in two affected sisters who inherited a BMP2 splice-altering variant, were observed across all reported families. Additionally, we observed similarity to the human phenotype of short stature and skeletal anomalies in a heterozygous Bmp2-knockout mouse model, suggesting that haploinsufficiency of BMP2 could be the primary phenotypic determinant in individuals with predicted truncating variants and deletions encompassing BMP2. These findings demonstrate the important role of BMP2 in human craniofacial, skeletal, and cardiac development and confirm that individuals heterozygous for BMP2 truncating sequence variants or deletions display a consistent distinct phenotype characterized by short stature and skeletal and cardiac anomalies without neurological deficits.
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http://dx.doi.org/10.1016/j.ajhg.2017.10.006DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5812889PMC
December 2017

Co-option of the cardiac transcription factor Nkx2.5 during development of the emu wing.

Nat Commun 2017 07 25;8(1):132. Epub 2017 Jul 25.

Murdoch Children's Research Institute, Royal Children's Hospital, Parkville, VIC, 3052, Australia.

The ratites are a distinctive clade of flightless birds, typified by the emu and ostrich that have acquired a range of unique anatomical characteristics since diverging from basal Aves at least 100 million years ago. The emu possesses a vestigial wing with a single digit and greatly reduced forelimb musculature. However, the embryological basis of wing reduction and other anatomical changes associated with loss of flight are unclear. Here we report a previously unknown co-option of the cardiac transcription factor Nkx2.5 to the forelimb in the emu embryo, but not in ostrich, or chicken and zebra finch, which have fully developed wings. Nkx2.5 is expressed in emu limb bud mesenchyme and maturing wing muscle, and mis-expression of Nkx2.5 throughout the limb bud in chick results in wing reductions. We propose that Nkx2.5 functions to inhibit early limb bud expansion and later muscle growth during development of the vestigial emu wing.The transcription factor Nkx2.5 is essential for heart development. Here, the authors identify a previously unknown expression domain for Nkx2.5 in the emu wing and explore its role in diminished wing bud development in the flightless emu, compared with three other birds that have functional wings.
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http://dx.doi.org/10.1038/s41467-017-00112-7DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5526984PMC
July 2017

Clinical and Molecular Characterisation of Children with Pierre Robin Sequence and Additional Anomalies.

Mol Syndromol 2016 Nov 15;7(6):322-328. Epub 2016 Sep 15.

Murdoch Childrens Research Institute, University of Melbourne, Melbourne, Vic., Australia; Department of Paediatrics, University of Melbourne, Melbourne, Vic., Australia; Royal Children's Hospital, Melbourne, Vic., Australia; Victorian Clinical Genetics Services, Melbourne, Vic., Australia.

Pierre Robin Sequence (PRS) is usually classified into syndromic and nonsyndromic groups, with a further subclassification of the nonsyndromic group into isolated PRS and PRS with additional anomalies (PRS-Plus). The aim of this research is to provide an accurate phenotypic characterisation of nonsyndromic PRS, specifically the PRS-Plus subgroup. We sought to examine the frequency of sequence variants in previously defined conserved noncoding elements (CNEs) in the putative enhancer region upstream of , the regulation of which has been associated with PRS phenotypes. We identified 141 children with nonsyndromic PRS at the Royal Children's Hospital, Melbourne from 1985 to 2012 using 2 databases. Clinical and demographic data were extracted by file review and children categorized as 'isolated PRS' or 'PRS-Plus'. A subset of children with PRS-Plus was selected for detailed phenotyping and DNA sequencing of the upstream CNEs. We found 83 children with isolated PRS and 58 with PRS-Plus. The most common PRS-Plus malformations involved the musculoskeletal and ocular systems. The most common coexisting craniofacial malformation was choanal stenosis/atresia. We identified 10 children with a family history of PRS or cleft palate. We found a single nucleotide substitution in a putative -binding site in one patient, but it was inherited from his phenotypically unaffected mother. PRS-Plus represents a broad phenotypic spectrum with uncertain pathogenesis. Dysmorphology assessment by a clinical geneticist is recommended. CNE sequence variants are rare in our cohort and are unlikely to play a significant role in the pathogenesis of PRS-Plus.
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http://dx.doi.org/10.1159/000449115DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5131331PMC
November 2016

Frontonasal Dysplasia: Towards an Understanding of Molecular and Developmental Aetiology.

Mol Syndromol 2016 Nov 29;7(6):312-321. Epub 2016 Oct 29.

Victorian Clinical Genetics Service, Royal Children's Hospital, University of Melbourne, Parkville, Vic., Australia; Department of Paediatrics, University of Melbourne, Parkville, Vic., Australia.

The complex anatomy of the skull and face arises from the requirement to support multiple sensory and structural functions. During embryonic development, the diverse component elements of the neuro- and viscerocranium must be generated independently and subsequently united in a manner that sustains and promotes the growth of the brain and sensory organs, while achieving a level of structural integrity necessary for the individual to become a free-living organism. While each of these individual craniofacial components is essential, the cranial and facial midline lies at a structural nexus that unites these disparately derived elements, fusing them into a whole. Defects of the craniofacial midline can have a profound impact on both form and function, manifesting in a diverse array of phenotypes and clinical entities that can be broadly defined as frontonasal dysplasias (FNDs). Recent advances in the identification of the genetic basis of FNDs along with the analysis of developmental mechanisms impacted by these mutations have dramatically altered our understanding of this complex group of conditions.
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http://dx.doi.org/10.1159/000450533DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5131330PMC
November 2016

Olfr603, an orphan olfactory receptor, is expressed in multiple specific embryonic tissues.

Gene Expr Patterns 2015 Sep-Nov;19(1-2):30-5. Epub 2015 Jun 23.

Murdoch Childrens Research Institute, Royal Children's Hospital, Parkville and Department of Paediatrics, University of Melbourne, Parkville, Australia. Electronic address:

Background: Olfactory receptors were initially believed to be expressed specifically within the olfactory neurons. However, accumulating genome-scale data has recently demonstrated more extensive expression. There are hundreds of olfactory receptor family members and the realisation of their widespread expression provides an opportunity to reveal new biology. However, existing data is predominantly based on RT-PCR, microarray and RNA-seq approaches and the details of tissue and cell-type specific expression are lacking.

Results: As a proof of principle, we selected Olfr603 for expression analysis. We generated an antibody against a non-conserved epitope of Olfr603 and characterised its expression in E8.5-E12.5 mouse embryos using immunohistochemistry. This analysis demonstrated a dynamic pattern of expression in diverse cell types within the developing embryo unrelated to the olfactory system. Expression was detected in migrating neural crest, endothelial precursors and vascular endothelium, endocardial cells, smooth muscle, neuroepithelium and within the ocular tissues. This complex distribution does not conform to any apparent germ layer or tissue origin.

Conclusions: This initial characterisation of Olfr603 expression highlights the potential for a broad role for this receptor in the development of many tissues.
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http://dx.doi.org/10.1016/j.gep.2015.06.002DOI Listing
September 2016

Collagen VI microfibril formation is abolished by an {alpha}2(VI) von Willebrand factor type A domain mutation in a patient with Ullrich congenital muscular dystrophy.

J Biol Chem 2010 Oct 21;285(43):33567-76. Epub 2010 Aug 21.

Departments of Paediatrics, Murdoch Childrens Research Institute, University of Melbourne, Royal Children’s Hospital, Parkville, Victoria 3052, Australia.

Collagen VI is an extracellular protein that most often contains the three genetically distinct polypeptide chains, α1(VI), α2(VI), and α3(VI), although three recently identified chains, α4(VI), α5(VI), and α6(VI), may replace α3(VI) in some situations. Each chain has a triple helix flanked by N- and C-terminal globular domains that share homology with the von Willebrand factor type A (VWA) domains. During biosynthesis, the three chains come together to form triple helical monomers, which then assemble into dimers and tetramers. Tetramers are secreted from the cell and align end-to-end to form microfibrils. The precise molecular mechanisms responsible for assembly are unclear. Mutations in the three collagen VI genes can disrupt collagen VI biosynthesis and matrix organization and are the cause of the inherited disorders Bethlem myopathy and Ullrich congenital muscular dystrophy. We have identified a Ullrich congenital muscular dystrophy patient with compound heterozygous mutations in α2(VI). The first mutation causes skipping of exon 24, and the mRNA is degraded by nonsense-mediated decay. The second mutation is a two-amino acid deletion in the C1 VWA domain. Recombinant C1 domains containing the deletion are insoluble and retained intracellularly, indicating that the mutation has detrimental effects on domain folding and structure. Despite this, mutant α2(VI) chains retain the ability to associate into monomers, dimers, and tetramers. However, we show that secreted mutant tetramers containing structurally abnormal C1 VWA domains are unable to associate further into microfibrils, directly demonstrating the critical importance of a correctly folded α2(VI) C1 domain in microfibril formation.
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http://dx.doi.org/10.1074/jbc.M110.152520DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2963345PMC
October 2010

Reduction of lysyl hydroxylase 3 causes deleterious changes in the deposition and organization of extracellular matrix.

J Biol Chem 2009 Oct 20;284(41):28204-11. Epub 2009 Aug 20.

Department of Biochemistry, P.O. Box 3000, University of Oulu, FI-90014 Oulu, Finland.

Lysyl hydroxylase 3 (LH3) is a multifunctional enzyme possessing lysyl hydroxylase, collagen galactosyltransferase, and glucosyltransferase (GGT) activities. We report here an important role for LH3 in the organization of the extracellular matrix (ECM) and cytoskeleton. Deposition of ECM was affected in heterozygous LH3 knock-out mouse embryonic fibroblasts (MEF(+/-)) and in skin fibroblasts collected from a member of a Finnish epidermolysis bullosa simplex (EBS) family known to be deficient in GGT activity. We show the GGT deficiency to be due to a transcriptional defect in one LH3 allele. The ECM abnormalities also lead to defects in the arrangement of the cytoskeleton in both cell lines. Ultrastructural abnormalities were observed in the skin of heterozygous LH3 knock-out mice indicating that even a moderate decrease in LH3 has deleterious consequences in vivo. The LH3 null allele in the EBS family member and the resulting abnormalities in the organization of the extracellular matrix, similar to those found in MEF(+/-), may explain the correlation between the severity of the phenotype and the decrease in GGT activity reported in this family.
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http://dx.doi.org/10.1074/jbc.M109.038190DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2788872PMC
October 2009

Collagen VI glycine mutations: perturbed assembly and a spectrum of clinical severity.

Ann Neurol 2008 Sep;64(3):294-303

Murdoch Childrens Research Institute and Department of Paediatrics, University of Melbourne, Royal Children's Hospital, Victoria, Australia.

Objective: The collagen VI muscular dystrophies, Bethlem myopathy and Ullrich congenital muscular dystrophy, form a continuum of clinical phenotypes. Glycine mutations in the triple helix have been identified in both Bethlem and Ullrich congenital muscular dystrophy, but it is not known why they cause these different phenotypes.

Methods: We studied eight new patients who presented with a spectrum of clinical severity, screened the three collagen VI messenger RNA for mutations, and examined collagen VI biosynthesis and the assembly pathway.

Results: All eight patients had heterozygous glycine mutations toward the N-terminal end of the triple helix. The mutations produced two assembly phenotypes. In the first patient group, collagen VI dimers accumulated in the cell but not the medium, microfibril formation in the medium was moderately reduced, and the amount of collagen VI in the extracellular matrix was not significantly altered. The second group had more severe assembly defects: some secreted collagen VI tetramers were not disulfide bonded, microfibril formation in the medium was severely compromised, and collagen VI in the extracellular matrix was reduced.

Interpretation: These data indicate that collagen VI glycine mutations impair the assembly pathway in different ways and disease severity correlates with the assembly abnormality. In mildly affected patients, normal amounts of collagen VI were deposited in the fibroblast matrix, whereas in patients with moderate-to-severe disability, assembly defects led to a reduced collagen VI fibroblast matrix. This study thus provides an explanation for how different glycine mutations produce a spectrum of clinical severity.
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http://dx.doi.org/10.1002/ana.21439DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2743946PMC
September 2008

Competency for nonsense-mediated reduction in collagen X mRNA is specified by the 3' UTR and corresponds to the position of mutations in Schmid metaphyseal chondrodysplasia.

Am J Hum Genet 2008 Mar 21;82(3):786-93. Epub 2008 Feb 21.

Murdoch Childrens Research Institute, University of Melbourne, Royal Children's Hospital, Parkville, Victoria 3052, Australia.

Nonsense-mediated decay (NMD) is a eukaryotic cellular RNA surveillance and quality-control mechanism that degrades mRNA containing premature stop codons (nonsense mutations) that otherwise may exert a deleterious effect by the production of dysfunctional truncated proteins. Collagen X (COL10A1) nonsense mutations in Schmid-type metaphyseal chondrodysplasia are localized in a region toward the 3' end of the last exon (exon 3) and result in mRNA decay, in contrast to most other genes in which terminal-exon nonsense mutations are resistant to NMD. We introduce nonsense mutations into the mouse Col10a1 gene and express these in a hypertrophic-chondrocyte cell line to explore the mechanism of last-exon mRNA decay of Col10a1 and demonstrate that mRNA decay is spatially restricted to mutations occurring in a 3' region of the exon 3 coding sequence; this region corresponds to where human mutations have been described. This localization of mRNA-decay competency suggested that a downstream region, such as the 3' UTR, may play a role in specifying decay of mutant Col10a1 mRNA containing nonsense mutations. We found that deleting any of the three conserved sequence regions within the 3' UTR (region I, 23 bp; region II, 170 bp; and region III, 76 bp) prevented mutant mRNA decay, but a smaller 13 bp deletion within region III was permissive for decay. These data suggest that the 3' UTR participates in collagen X last-exon mRNA decay and that overall 3' UTR configuration, rather than specific linear-sequence motifs, may be important in specifying decay of Col10a1 mRNA containing nonsense mutations.
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http://dx.doi.org/10.1016/j.ajhg.2008.01.006DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2427218PMC
March 2008

Molecular consequences of dominant Bethlem myopathy collagen VI mutations.

Ann Neurol 2007 Oct;62(4):390-405

Murdoch Childrens Research Institute and Department of Paediatrics, University of Melbourne, Royal Children's Hospital, Parkville, Victoria, Australia.

Objective: Dominant mutations in the three collagen VI genes cause Bethlem myopathy, a disorder characterized by proximal muscle weakness and commonly contractures of the fingers, wrists, and ankles. Although more than 20 different dominant mutations have been identified in Bethlem myopathy patients, the biosynthetic consequences of only a subset of these have been studied, and in many cases, the pathogenic mechanisms remain unknown.

Methods: We have screened fourteen Bethlem myopathy patients for collagen VI mutations and performed detailed analyses of collagen VI biosynthesis and intracellular and extracellular assembly.

Results: Collagen VI abnormalities were identified in eight patients. One patient produced around half the normal amount of alpha1(VI) messenger RNA and reduced amounts of collagen VI protein. Two patients had a previously reported mutation causing skipping of COL6A1 exon 14, and three patients had novel mutations leading to in-frame deletions toward the N-terminal end of the triple-helical domain. These mutations have different and complex effects on collagen VI intracellular and extracellular assembly. Two patients had single amino acid substitutions in the A-domains of COL6A2 and COL6A3. Collagen VI intracellular and extracellular assembly was normal in one of these patients.

Interpretation: The key to dissecting the pathogenic mechanisms of collagen VI mutations lies in detailed analysis of collagen VI biosynthesis and assembly. The majority of mutations result in secretion and deposition of structurally abnormal collagen VI. However, one A-domain mutation had no detectable effect on assembly, suggesting that it acts by compromising collagen VI interactions in the extracellular matrix of muscle.
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http://dx.doi.org/10.1002/ana.21213DOI Listing
October 2007

Secretion and assembly of type IV and VI collagens depend on glycosylation of hydroxylysines.

J Biol Chem 2007 Nov 14;282(46):33381-33388. Epub 2007 Sep 14.

Department of Biocenter Oulu, University of Oulu, Oulu, FI-90014, Finland; Department of Biochemistry, University of Oulu, Oulu, FI-90014, Finland. Electronic address:

Most lysines in type IV and VI collagens are hydroxylated and glycosylated, but the functions of these unique galactosylhydroxylysyl and glucosylgalactosylhydroxylysyl residues are poorly understood. The formation of glycosylated hydroxylysines is catalyzed by multifunctional lysyl hydroxylase 3 (LH3) in vivo, and we have used LH3-manipulated mice and cells as models to study the function of these carbohydrates. These hydroxylysine-linked carbohydrates were shown recently to be indispensable for the formation of basement membranes (Ruotsalainen, H., Sipilä, L., Vapola, M., Sormunen, R., Salo, A. M., Uitto, L., Mercer, D. K., Robins, S. P., Risteli, M., Aszodi, A., Fässler, R., and Myllylä, R. (2006) J. Cell Sci. 119, 625-635). Analysis of LH3 knock-out embryos and cells in this work indicated that loss of glycosylated hydroxylysines prevents the intracellular tetramerization of type VI collagen and leads to impaired secretion of type IV and VI collagens. Mice lacking the LH activity of LH3 produced slightly underglycosylated type IV and VI collagens with abnormal distribution. The altered distribution and aggregation of type VI collagen led to similar ultrastructural alterations in muscle to those detected in collagen VI knockout and some Ullrich congenital muscular dystrophy patients. Our results provide new information about the function of hydroxylysine-linked carbohydrates of collagens, indicating that they play an important role in the secretion, assembly, and distribution of highly glycosylated collagen types.
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http://dx.doi.org/10.1074/jbc.M704198200DOI Listing
November 2007

Variable penetrance of COL6A1 null mutations: implications for prenatal diagnosis and genetic counselling in Ullrich congenital muscular dystrophy families.

Neuromuscul Disord 2007 Jul 29;17(7):547-57. Epub 2007 May 29.

The Neurogenetics Research Unit, Children's Hospital, Westmead, Sydney, Australia.

Collagen VI mutations cause mild Bethlem myopathy and severe, progressive Ullrich congenital muscular dystrophy (UCMD). We identified a novel homozygous COL6A1 premature termination mutation in a UCMD patient that causes nonsense-mediated mRNA decay. Collagen VI microfibrils cannot be detected in muscle or fibroblasts. The parents are heterozygous carriers of the mutation and their fibroblasts produce reduced amounts of collagen VI. The molecular findings in the parents are analogous to those reported for a heterozygous COL6A1 premature termination mutation that causes Bethlem myopathy. However, the parents of our UCMD proband are clinically normal. The proband's brother, also a carrier, has clinical features consistent with a mild collagen VI phenotype. Following a request for prenatal diagnosis in a subsequent pregnancy we found the fetus was a heterozygous carrier indicating that it would not be affected with severe UCMD. COL6A1 premature termination mutations exhibit variable penetrance necessitating a cautious approach to genetic counselling.
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http://dx.doi.org/10.1016/j.nmd.2007.03.017DOI Listing
July 2007

Dominant collagen VI mutations are a common cause of Ullrich congenital muscular dystrophy.

Hum Mol Genet 2005 Jan 24;14(2):279-93. Epub 2004 Nov 24.

Cell and Matrix Biology, Murdoch Childrens Research Institute and Department of Paediatrics, University of Melbourne, Royal Children's Hospital, Parkville, Victoria, Australia.

Mutations in the three collagen VI genes COL6A1, COL6A2 and COL6A3 cause Bethlem myopathy and Ullrich congenital muscular dystrophy (UCMD). UCMD, a severe disorder characterized by congenital muscle weakness, proximal joint contractures and marked distal joint hyperextensibility, has been considered a recessive condition, and homozygous or compound heterozygous mutations have been defined in COL6A2 and COL6A3. In contrast, the milder disorder Bethlem myopathy shows clear dominant inheritance and is caused by heterozygous mutations in COL6A1, COL6A2 and COL6A3. This model, where dominant mutations cause mild Bethlem myopathy and recessive mutations cause severe UCMD was recently challenged when a patient with UCMD was shown to have a heterozygous in-frame deletion in COL6A1. We have studied five patients with a clinical diagnosis of UCMD. Three patients had heterozygous in-frame deletions in the N-terminal region of the triple helical domain, one in the alpha1(VI) chain, one in alpha2(VI) and one in alpha3(VI). Collagen VI protein biosynthesis and assembly studies showed that these mutations act in a dominant negative fashion and result in severe collagen VI matrix deficiencies. One patient had recessive amino acid changes in the C2 subdomain of alpha2(VI), which prevented collagen VI assembly. No collagen VI mutations were found in the fifth patient. These data demonstrate that rather than being a rare cause of UCMD, dominant mutations are common in UCMD, now accounting for four of the 14 published cases. Mutation detection in this disorder remains critical for accurate genetic counseling of patients and their families.
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http://dx.doi.org/10.1093/hmg/ddi025DOI Listing
January 2005