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M Muenke

Publications and source records attributed to M Muenke.

At least 37 records · Page 2Linked to original sources
PubMed2000

Genetic approaches to understanding brain development: holoprosencephaly as a model.

Holoprosencephaly (HPE) is the most common major developmental defect of the forebrain in humans. Clinical expression is variable, ranging from a small brain with a single cerebral ventricle and cyclopia to clinically unaffected carriers in familial HPE. Significant etiologic heterogeneity exists in HPE and includes both genetic and environmental causes. Defects in the cell signaling pathway involving the Sonic Hedgehog (SHH) gene, as well as defects in the cholesterol biosynthesis have been shown to cause HPE in humans. More recently, HPE genes from additional signaling pathways have been identified. These discoveries and current genetic approaches serve as a paradigm for studying normal and abnormal brain morphogenesis. MRDD Research Reviews 6:15-21, 2000.

Brain↗
PubMed2000

Mutations in holoprosencephaly.

Holoprosencephaly (HPE) is the most common developmental defect of the forebrain and midface in humans. In holoprosencephaly the cerebral hemispheres of the brain fail to separate into distinct left and right hemispheres. This malformation is due to the improper specification and formation of the forebrain during early development. When one considers the great number and kinds of genetic interactions that must occur to properly pattern the developing forebrain, it is not surprising that HPE is extremely heterogeneous. In addition to teratogenic agents, several genes are implicated as the cause of HPE. At least 12 different loci have been associated with HPE and now several distinct human genes for holoprosencephaly have been identified. These genes include Sonic Hedgehog (SHH), ZIC2, SIX3, and TG-interacting factor (TGIF). Here we present an overview of the presently known genes causing human holoprosencephaly. We discuss their functional role in development of the forebrain and summarize the mutations and polymorphisms that have been identified within them. Hum Mutat 16:99-108, 2000. Published 2000 Wiley-Liss, Inc.

Animals↗
PubMed2000

Genetics of ventral forebrain development and holoprosencephaly.

The disease holoprosencephaly is the basis of the most common structural anomaly of the developing forebrain in humans. Numerous teratogens when administered during early gastrulation, have been associated with this condition. Recent studies have characterized molecules expressed in the prechordal plate which are critical for normal brain formation. Perturbation of signaling pathways involving these molecules have been shown to cause holoprosencephaly in humans and other organisms.

Animals↗
PubMed2000

Mutations in TGIF cause holoprosencephaly and link NODAL signalling to human neural axis determination.

Holoprosencephaly (HPE) is the most common structural defect of the developing forebrain in humans (1 in 250 conceptuses, 1 in 16,000 live-born infants). HPE is aetiologically heterogeneous, with both environmental and genetic causes. So far, three human HPE genes are known: SHH at chromosome region 7q36 (ref. 6); ZIC2 at 13q32 (ref. 7); and SIX3 at 2p21 (ref. 8). In animal models, genes in the Nodal signalling pathway, such as those mutated in the zebrafish mutants cyclops (refs 9,10), squint (ref. 11) and one-eyed pinhead (oep; ref. 12), cause HPE. Mice heterozygous for null alleles of both Nodal and Smad2 have cyclopia. Here we describe the involvement of the TG-interacting factor (TGIF), a homeodomain protein, in human HPE. We mapped TGIF to the HPE minimal critical region in 18p11.3. Heterozygous mutations in individuals with HPE affect the transcriptional repression domain of TGIF, the DNA-binding domain or the domain that interacts with SMAD2. (The latter is an effector in the signalling pathway of the neural axis developmental factor NODAL, a member of the transforming growth factor-beta (TGF-beta) family.) Several of these mutations cause a loss of TGIF function. Thus, TGIF links the NODAL signalling pathway to the bifurcation of the human forebrain and the establishment of ventral midline structures.

Animals↗
PubMed2000

Loss-of-function mutations in the EGF-CFC gene CFC1 are associated with human left-right laterality defects.

All vertebrates display a characteristic asymmetry of internal organs with the cardiac apex, stomach and spleen towards the left, and the liver and gall bladder on the right. Left-right (L-R) axis abnormalities or laterality defects are common in humans (1 in 8,500 live births). Several genes (such as Nodal, Ebaf and Pitx2) have been implicated in L-R organ positioning in model organisms. In humans, relatively few genes have been associated with a small percentage of human situs defects. These include ZIC3 (ref. 5), LEFTB (formerly LEFTY2; ref. 6) and ACVR2B (encoding activin receptor IIB; ref. 7). The EGF-CFC genes, mouse Cfc1 (encoding the Cryptic protein; ref. 9) and zebrafish one-eyed pinhead (oep; refs 10, 11) are essential for the establishment of the L-R axis. EGF-CFC proteins act as co-factors for Nodal-related signals, which have also been implicated in L-R axis development. Here we identify loss-of-function mutations in human CFC1 (encoding the CRYPTIC protein) in patients with heterotaxic phenotypes (randomized organ positioning). The mutant proteins have aberrant cellular localization in transfected cells and are functionally defective in a zebrafish oep-mutant rescue assay. Our findings indicate that the essential role of EGF-CFC genes and Nodal signalling in left-right axis formation is conserved from fish to humans. Moreover, our results support a role for environmental and/or genetic modifiers in determining the ultimate phenotype in humans.

Abnormalities, Multiple↗
PubMed2000

ARP3beta, the gene encoding a new human actin-related protein, is alternatively spliced and predominantly expressed in brain neuronal cells.

A cDNA encoding a new human actin-related protein (ARP) was cloned. The corresponding protein is highly conserved with the previously described ARP3 protein, suggesting that it represents a second isoform of the human ARP3 subfamily. This new actin-related protein was subsequently named ARP3beta and represents the second example of multiple isoforms of an actin-related protein in a single organism. The ARP3beta gene was mapped to chromosome band 7q34, centromeric to Sonic Hedgehog. Gene structure analysis revealed that at least part of the observed ARP3beta mRNA heterogeneity is caused by alternative splicing resulting in exon skipping. Transcripts produced after exon 2 skipping are predicted to encode truncated products, whose functionality is still unclear. An ARP3beta pseudogene was detected on chromosome 2p11 by database searching. Several ARP3beta mRNA species were detected by Northern blotting and their abundance varied importantly among tissues: the highest expression levels were detected in fetal and adult brain, whereas lower levels were observed in liver, muscle and pancreas. In contrast, ARP3 mRNAs were detected in all tissues tested. Using in situ hybridization, the expression of ARP3beta in brain was shown to be restricted to neurons and epithelial cells from choroid plexus. This suggests a specific function for ARP3beta in the physiology of the development and/or maintenance of distinct subsets of nerve cells.

Actin-Related Protein 3↗
PubMed2000

Fibrodysplasia ossificans progressiva, a heritable disorder of severe heterotopic ossification, maps to human chromosome 4q27-31.

Fibrodysplasia ossificans progressiva (FOP) is a severely disabling, autosomal-dominant disorder of connective tissue and is characterized by postnatal progressive heterotopic ossification of muscle, tendon, ligament, and fascia and by congenital malformation of the great toes. To identify the chromosomal location of the FOP gene, we conducted a genomewide linkage analysis, using four affected families with a total of 14 informative meioses. Male-to-male transmission of the FOP phenotype excluded X-linked inheritance. Highly polymorphic microsatellite markers covering all human autosomes were amplified by use of PCR. The FOP phenotype is linked to markers located in the 4q27-31 region (LOD score 3.10 at recombination fraction 0). Crossover events localize the putative FOP gene within a 36-cM interval bordered proximally by D4S1625 and distally by D4S2417. This interval contains at least one gene involved in the bone morphogenetic protein-signaling pathway.

Chromosome Mapping↗
PubMed2000

The genomic structure, chromosome location, and analysis of the human DKK1 head inducer gene as a candidate for holoprosencephaly.

Holoprosencephaly (HPE) is the most common developmental defect of the brain and face in humans. Here we report the analysis of the human ortholog of dkk-1 as a candidate gene for HPE. We determined the genomic structure of the human gene DKK1 and mapped it to chromosome 10q11.2. Functional analysis of four missense mutations identified in HPE patients revealed preserved activity in head induction assays in frogs suggesting a limited role for this gene in HPE pathogenesis.

Amino Acid Sequence↗
PubMed1999

Familial dementia caused by polymerization of mutant neuroserpin.

Aberrant protein processing with tissue deposition is associated with many common neurodegenerative disorders; however, the complex interplay of genetic and environmental factors has made it difficult to decipher the sequence of events linking protein aggregation with clinical disease. Substantial progress has been made toward understanding the pathophysiology of prototypical conformational diseases and protein polymerization in the superfamily of serine proteinase inhibitors (serpins). Here we describe a new disease, familial encephalopathy with neuroserpin inclusion bodies, characterized clinically as an autosomal dominantly inherited dementia, histologically by unique neuronal inclusion bodies and biochemically by polymers of the neuron-specific serpin, neuroserpin. We report the cosegregation of point mutations in the neuroserpin gene (PI12) with the disease in two families. The significance of one mutation, S49P, is evident from its homology to a previously described serpin mutations, whereas that of the other, S52R, is predicted by modelling of the serpin template. Our findings provide a molecular mechanism for a familial dementia and imply that inhibitors of protein polymerization may be effective therapies for this disorder and perhaps for other more common neurodegenerative diseases.

Biopolymers↗
PubMed1999

Molecular mechanisms of holoprosencephaly.

Holoprosencephaly (HPE) is the most common developmental defect of the forebrain in humans. Several distinct human genes for holoprosencephaly have now been identified. They include Sonic hedgehog (SHH), ZIC2, and SIX3. Many additional genes involved in forebrain development are rapidly being cloned and characterized in model vertebrate organisms. These include Patched (Ptc), Smoothened (Smo), cubitus interuptus (ci)/Gli, wingless (wg/Wnt, decapentaplegic (dpp)/BMP, Hedgehog interacting protein (Hip), nodal, Smads, One-eyed pinhead (Oep), and TG-Interacting Factor (TGIF). However, further analysis is needed before their roles in HPE can be established. Here we present an overview of the presently known genes causing human holoprosencephaly and describe candidate genes involved in forebrain development identified in other systems. A model is discussed for how these genes may interact within and between several different signaling pathways to direct the formation of the forebrain.

Gene Expression Regulation, Developmental↗
PubMed1999

The molecular genetics of holoprosencephaly: a model of brain development for the next century.

The recent identification of some of the human holoprosencephaly genes is beginning to elucidate the intricate developmental programs that pattern normal and abnormal brain development. Here we present some of these advances in the context of our present understanding and conclude with some speculations regarding the direction for future investigations. We are living in a tremendously exciting time in medicine with the rapid application of molecular genetic approaches to the understanding of human disease. It is the purpose of this review to stress the underlying principals of our approach at a level that can be readily appreciated by colleagues who themselves are experts in brain anatomy but not necessarily the molecular genetics of brain development.

Central Nervous System↗
PubMed1999

Analysis of the mutational spectrum of the FGFR2 gene in Pfeiffer syndrome.

Pfeiffer syndrome (PS) is one of the classical craniosynostosis syndromes correlated with specific mutations in the human fibroblast growth factor receptor (FGFR) genes, FGFR1 and FGFR2. In this study, we set out to examine the exons in FGFR2 most commonly associated with mutations in PS, exons IIIa and IIIc, in a panel of 78 unrelated individuals with PS by the most sensitive method (direct DNA sequencing). We have identified a total of 18 different mutations among 40 patients; eight of these mutations have not been previously described. The mutational spectrum displays a non-random character with the frequent involvement of cysteine codons.

Acrocephalosyndactylia↗
PubMed1999

Structure of the human Lanosterol synthase gene and its analysis as a candidate for holoprosencephaly (HPE1).

Holoprosencephaly (HPE) is the most common birth defect of the brain in humans. It involves various degrees of incomplete separation of the cerebrum into distinct left and right halves, and it is frequently accompanied by craniofacial anomalies. The HPE1 locus in human chromosome 21q22.3 is one of a dozen putative genetic loci implicated in causing HPE. Here, we report the complete gene structure of the human lanosterol synthase (LS) gene, which is located in this interval, and present its mutational analysis in HPE patients. We considered LS an excellent candidate HPE gene because of the requirement for cholesterol modification of the Sonic Hedgehog protein for the correct patterning activity of this HPE-associated protein. Despite extensive pedigree analysis of numerous polymorphisms, as well as complementation studies in yeast on one of the missense mutations, we find no evidence that the LS gene is in fact HPE1, implicating another gene located in this chromosomal region in HPE pathogenesis.

Base Sequence↗
PubMed1999

Genes and chromosomal breakpoints in the Langer-Giedion syndrome region on human chromosome 8.

The tricho-rhino-phalangeal syndrome type II (TRPS II, or Langer-Giedion syndrome) is an example of contiguous gene syndromes, as it comprises the clinical features of two autosomal dominant diseases, TRPS I and a form of multiple cartilaginous exostoses caused by mutations in the EXT1 gene. We have constructed a contig of cosmid, lambda-phage, PAC, and YAC clones, which covers the entire TRPS I critical region. Using these clones we identified a novel submicroscopic deletion in a TRPS I patient and refined the proximal border of the minimal TRPS1 gene region by precisely mapping the inversion breakpoint of another patient. As a first step towards a complete inventory of genes in the Langer-Giedion syndrome chromosome region (LGCR) with the ultimate aim to identify the TRPS1 gene, we analyzed 23 human expressed sequence tags (ESTs) and four genes (EIF3S3, RAD21, OPG, CXIV) which had been assigned to human 8q24.1. Our analyses indicate that the LGCR is gene-poor, because none of the ESTs and genes map to the minimal TRPS1 gene region and only two of these genes, RAD21 and EIF3S3, are located within the shortest region of deletion overlap of TRPS II patients. Two genes, OPG and CXIV, which are deleted only in some patients with TRPS II may contribute to the clinical variability of this syndrome.

Child↗
PubMed1999

Mutations in the homeodomain of the human SIX3 gene cause holoprosencephaly.

Holoprosencephaly (HPE) is a common, severe malformation of the brain that involves separation of the central nervous system into left and right halves. Mild HPE can consist of signs such as a single central incisor, hypotelorism, microcephaly, or other craniofacial findings that can be present with or without associated brain malformations. The aetiology of HPE is extremely heterogeneous, with the proposed participation of a minimum of 12 HPE-associated genetic loci as well as the causal involvement of specific teratogens acting at the earliest stages of neurulation. The HPE2 locus was recently characterized as a 1-Mb interval on human chromosome 2p21 that contained a gene associated with HPE. A minimal critical region was defined by a set of six overlapping deletions and three clustered translocations in HPE patients. We describe here the isolation and characterization of the human homeobox-containing SIX3 gene from the HPE2 minimal critical region (MCR). We show that at least 2 of the HPE-associated translocation breakpoints in 2p21 are less than 200 kb from the 5' end of SIX3. Mutational analysis has identified four different mutations in the homeodomain of SIX3 that are predicted to interfere with transcriptional activation and are associated with HPE. We propose that SIX3 is the HPE2 gene, essential for the development of the anterior neural plate and eye in humans.

Amino Acid Sequence↗
PubMed1999

The mutational spectrum of the sonic hedgehog gene in holoprosencephaly: SHH mutations cause a significant proportion of autosomal dominant holoprosencephaly.

Holoprosencephaly (HPE) is a common developmental anomaly of the human forebrain and midface where the cerebral hemispheres fail to separate into distinct left and right halves. We have previously reported haploinsufficiency for Sonic Hedgehog ( SHH ) as a cause for HPE. We have now performed mutational analysis of the complete coding region and intron-exon junctions of the SHH gene in 344 unrelated affected individuals. Herein, we describe 13 additional unrelated affected individuals with SHH mutations, including nonsense and missense mutations, deletions and an insertion. These mutations occur throughout the extent of the gene. No specific genotype-phenotype association is evident based on the correlation of the type or position of the mutations. In conjunction with our previous studies, we have identified a total of 23 mutations in 344 unrelated cases of HPE. They account for 14 cases of familial HPE and nine cases of sporadic HPE. Mutations in SHH were detected in 10 of 27 (37%) families showing autosomal dominant transmission of the HPE spectrum, based on structural anomalies. Interestingly, three of the patients with an SHH mutation also had abnormalities in another gene that is expressed during forebrain development. We suggest that the interactions of multiple gene products and/or environmental elements may determine the final phenotypic outcome for a given individual and that variations among these factors may cause the wide variability in the clinical features seen in HPE.

Amino Acid Sequence↗
PubMed1998

Phenotype of the fibroblast growth factor receptor 2 Ser351Cys mutation: Pfeiffer syndrome type III.

We present a patient with pansynostosis, hydrocephalus, seizures, extreme proptosis with luxation of the eyes out of the lids, apnea and airway obstruction, intestinal non-rotation, and severe developmental delay. His skeletal abnormalities include bilateral elbow ankylosis, radial head dislocation, and unilateral broad and deviated first toe. The phenotype of this patient is consistent with that previously reported in Pfeiffer syndrome type III, but is unusual for the lack of broad thumbs. Our patient most closely resembles the case described by Kerr et al. [1996: Am J Med Genet 66:138-143] as Pfeiffer syndrome type III with normal thumbs. Mutations in the genes for fibroblast growth factor receptors (FGFR) 1 and 2 have previously been seen in patients with Pfeiffer syndrome type I. The mutation identified in our patient, Ser351Cys in FGFR2, represents the first reported cause of Pfeiffer syndrome type III. An identical mutation was described once previously by Pulleyn et al., in a patient whose brief clinical description included cloverleaf skull, significant developmental delay, and normal hands and feet [Eur. J. Hum. Genet. 4: 283-291, 1996]. In our patient, previously performed single-strand conformation polymorphism analysis failed to detect a band shift; the mutation was identified only after independent sequence analysis.

Abnormalities, Multiple↗