Patrice Bouvagnet

Mapping of a New Locus for Autosomal Recessive Demyelinating Charcot-Marie-Tooth Disease to 19q13.1-13.3 in a Large Consanguineous Lebanese Family: Exclusion of MAG as a Candidate Gene

Autosomal recessive Charcot-Marie-Tooth disease (CMT) type 4 (CMT4) is a complex group of demyelinating hereditary motor and sensory neuropathies presenting genetic heterogeneity. Five different subtypes that correspond to six different chromosomal locations have been described. We hereby report a large inbred Lebanese family affected with autosomal recessive CMT4, in whom we have excluded linkage to the already-known loci. The results of a genomewide search demonstrated linkage to a locus on chromosome 19q13.1-13.3, over an 8.5-cM interval between markers D19S220 and D19S412. A maximum pairwise LOD score of 5.37 for marker D19S420, at recombination fraction [theta].00, and a multipoint LOD score of 10.3 for marker D19S881, at straight theta = .00, strongly supported linkage to this locus. Clinical features and the results of histopathologic studies confirm that the disease affecting this family constitutes a previously unknown demyelinating autosomal recessive CMT subtype known as CMT4F. The myelin-associated glycoprotein (MAG) gene, located on 19q13.1 and specifically expressed in the CNS and the peripheral nervous system, was ruled out as being the gene responsible for this form of CMT.

A new autosomal recessive non-progressive congenital cerebellar ataxia associated with mental retardation, optic atrophy, and skin abnormalities (CAMOS) maps to chromosome 15q24-q26 in a large consanguineous Lebanese Druze family

Congenital cerebellar ataxias are a heterogeneous group of non-progressive disorders characterized by hypotonia and developmental delay followed by the appearance of ataxia, and often associated with dysarthria, mental retardation, and atrophy of the cerebellum. We report the mapping of a disease gene in a large inbred Lebanese Druze family, with five cases of a new form of non-progressive autosomal recessive congenital ataxia associated with optic atrophy, severe mental retardation, and structural skin abnormalities, to a 3.6-cM interval on chromosome 15q24–15q26.

MMP21 is mutated in human heterotaxy and is required for normal left-right asymmetry in vertebrates

Heterotaxy results from a failure to establish normal left-right asymmetry early in embryonic development. By whole-exome sequencing, whole-genome sequencing and high-throughput cohort resequencing, we identified recessive mutations in MMP21 (encoding matrix metallopeptidase 21) in nine index cases with heterotaxy. In addition, Mmp21-mutant mice and mmp21-morphant zebrafish displayed heterotaxy and abnormal cardiac looping, respectively, suggesting a new role for extracellular matrix remodeling in the establishment of laterality in vertebrates.

Nonprogressive autosomal recessive ataxia maps to chromosome 9q34-9qter in a large consanguineous Lebanese family.

Congenital ataxias are a heterogeneous group of predominantly nonprogressive disorders characterized by hypotonia, developmental delay followed by the appearance of ataxia, and often associated with dysarthria, mental retardation, and atrophy of the cerebellum. We performed a genome‐wide screen on a large inbred Lebanese family presenting a nonprogressive autosomal recessive congenital cerebellar ataxia associated with short stature (MIM 213200), already described by Mégarbané and colleagues. 1 The disease locus was assigned to a 12.1 cM interval on chromosome 9q34‐9qter between D9S67 and D9S312. Differential diagnosis with other hereditary ataxias linked to the same region is discussed.

Autosomal dominant secundum atrial septal defect with various cardiac and noncardiac defects: A new midline disorder

We report on a Lebanese family in which 12 persons had an atrial septal defect and various cardiac and noncardiac anomalies. Cardiac anomalies are left axis deviation of QRS, right bundle branch block, atrial fibrillation, Wolff-Parkinson-White syndrome, nodal atrioventricular rhythm, aortic stenosis, pulmonic valve stenosis, mitral stenosis (Lutembacher syndrome), and low implantation of the tricuspid valve (Ebstein disease). Noncardiac abnormalities consisted specially of the presence of hypertelorism, cleft lip, and pectus excavatum. This combination appears to constitute a hitherto undescribed autosomal dominant midline disorder of the heart and upper half of the body with almost full penetrance and variable expressivity. The mutation does not map to any known locus involved in atrial septal defect or conduction block.

Isolation, in silico characterization and chromosomal localization of a group of cDNAs from ciliated epithelial cells after in vitro ciliogenesis

BackgroundImmotile cilia syndrome (ICS) or primary ciliary dyskinesia (PCD) is an autosomal recessive disorder in humans in which the beating of cilia and sperm flagella is impaired. Ciliated epithelial cell linings are present in many tissues. To understand ciliary assembly and motility, it is important to isolate those genes involved in the process.ResultsTotal RNA was isolated from cultured ciliated nasal epithelial cells after in vitro ciliogenesis and expressed sequenced tags (ESTs) were generated. The functions and locations of 63 of these ESTs were derived by BLAST from two public databases. These ESTs are grouped into various classes. One group has high homology not only with the mitochondrial genome but also with one or more chromosomal DNAs, suggesting that very similar genes, or genes with very similar domains, are expressed from both mitochondrial and nuclear DNA. A second class comprises genes with complete homology with part of a known gene, suggesting that they are the same genes. A third group has partial homology with domains of known genes. A fourth group, constituting 33% of the ESTs characterized, has no significant homology with any gene or EST in the database.ConclusionsWe have shown that sufficient information about the location of ESTs could be derived electronically from the recently completed human genome sequences. This strategy of EST localization should be significantly useful for mapping and identification of new genes in the forthcoming human genome sequences with the vast number of ESTs in the dbEST database.

Assembling and gap filling of unordered genome sequences through gene checking

BackgroundThe first draft of human genome sequencing is complete. A large amount of DNA sequences are already available in the database but these are not ordered and assembled. In many cases, these sequences are shorter sequences (ranging from 10kb to 100kb) and are separated by NNNNNN. Also a considerable amount of gaps are to be filled in the subsequent years. Even after generating raw data, properly ordered, finished available sequences, are enormous tasks and expected to take another 2 years.ResultsHere, we describe a simple way to order random genome sequences and to trace gaps. These gaps could be filled by subsequent hybridizations and sequencing. These could be achieved by a simple method by three steps. 1) Selection of large cDNAs in the database (from lower organisms to human). 2) Blasting with these large cDNAs to the unordered human genomic sequences (raw BAC DNA sequences or large DNA fragments) . 3) Ordering these BACs DNA sequences or large DNA fragments based on the homology with cDNA sequences to maintain the continuity of exonic sequences. Homologous exons could also be taken into account on the basis of evolutionary conservacy when other organisms sequence except human, would be used for blasting. Any discontinuity in the exonic sequences denote possible gaps in between two BACs or two sequences.ConclusionsIn this way a large number of BACs could be arranged. Subsequently gaps could be traced and filled by further hybridizations and sequencing.

TOUT-DE-TRAVERS (TDT): A novel protease mutated in patients with heterotaxy drives left-right asymmetry upstream of Nodal signalling

However, recent studies in SMA animal models suggest that motor neuron degeneration is the result of cumulative dysfunctions in different cell types. We and others have shown that motor neurons in zebrafish SMN morphants initially form normally but later develop abnormal axon morphology, rendering them unable to innervate the muscles. Here we show that morpholino knockdown of SMN also results in an early down-regulation of pax6a, sox2 and nestin, which are genes important for general neuron progenitor maintenance and differentiation. Whole-mount in situ hybridization (WISH) suggests that defects in differentiation are restricted to subtypes of ventral interneurons that are located in the vicinity of motor neurons and express the post-mitotic markers eng1b, pitx2, gata3 and sim1a. These pre-motor interneurons were found to be reduced in number and dorsal gata3 interneurons were ectopically localized. Consistent with this, immunostaining for the post-mitotic differentiation marker HuC/D revealed widespread defects in neuron organization throughout the spinal cord. Importantly, ubiquitous overexpression of a mCherry-Smn fusion protein rescued the number of affected interneurons as well as the aberrant motor axon morphology associated with SMN knockdown. Although the functional consequences of the described interneuron defects on motor neuron activity and degeneration remain to be addressed, our data implicate pre-motor interneuron defects in a zebrafish model for SMA.

Human Genetics of d-Transposition of the Great Arteries

Dextro-transposition of the great arteries (d-TGA) is one of the rare congenital heart diseases (CHD) which benefits from early neonatal diagnosis because d-TGA requires rapid postnatal catheter procedure. In that respect, detecting parental genetic predisposing factors would contribute to focusing prenatal echographical attention to the early detection of d-TGA cases. A high male to female ratio and a high recurrence risk of d-TGA in the context of heterotaxy suggest the impact of genetic factors although familial cases of d-TGA are exceptional. Since the late 1990s, a growing list of genes and chromosomal regions was associated with d-TGA among which the ZIC3 gene. Although this gene is located on the X chromosome, ZIC3 (Zic family member 3) does not explain the male preponderance in d-TGA. d-TGA causal genes are involved in many different cellular pathways and can be provisionally sorted in two groups: those which disrupt the function of the embryonic node cilia and those which are downstream of this major embryological process of lateralization. Many more genes or gene factors remain to be discovered in d-TGA and related CHD because only a small percentage of d-TGA is yet genetically resolved.