Service de Cytogenetique Constitutionnelle

Sainte-Foy-lès-Lyon, France

Service de Cytogenetique Constitutionnelle

Sainte-Foy-lès-Lyon, France
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Roux A.-F.,Montpellier University Hospital Center | Roux A.-F.,French Institute of Health and Medical Research | Faugere V.,Montpellier University Hospital Center | Vache C.,Montpellier University Hospital Center | And 23 more authors.
Investigative Ophthalmology and Visual Science | Year: 2011

Purpose. The purpose of this study was to establish the mutation spectrum of an Usher type I cohort of 61 patients from France and to describe a diagnostic strategy, including a strategy for estimating the pathogenicity of sequence changes. Methods. To optimize the identification of Usher (USH)-causative mutations, taking into account the genetic heterogeneity, preliminary haplotyping at the five USH1 loci was performed to prioritize the gene to be sequenced, as previously described. Coding exons and flanking intronic sequences were sequenced and, where necessary, semiquantitative PCR and multiplex ligation-dependent probe amplification (MLPA) were performed to detect large genomic rearrangements. Results. Four years ' experience confirms that the chosen approach provides an efficient diagnostic service. Sixty-one patients showed an abnormal genotype in one of the five USH1 genes. Genetic heterogeneity was confirmed, and, although MYO7A remains the major gene, involvement of other genes is considerable. Distribution of missense, splicing, premature termination codons (PTCs; due to point substitution and small deletions/ or insertions), and large genomic alterations was determined among the USH genes and clearly highlights the need to pay special attention to the diagnostic approach and interpretation, depending on the mutated gene. Conclusions. Over the 4 years of a diagnostic service offering USH1 patient testing, pathogenic genotypes were identified in most cases (>90%). The complexity and heterogeneity of mutations reinforces the need for a comprehensive approach. Because 32% of the mutations are newly described, the results show that a screening strategy based on known mutations would have solved less than 55% of the cases. © 2011 The Association for Research in Vision and Ophthalmology, Inc.

Bonnet C.,Nancy University Hospital Center | Andrieux J.,Lille University Hospital Center | Beri-Dexheimer M.,Nancy University Hospital Center | Leheup B B.,Nancy University Hospital Center | And 25 more authors.
Journal of Medical Genetics | Year: 2010

Background: Genome-wide screening of large patient cohorts with mental retardation using microarray-based comparative genomic hybridisation (array-CGH) has recently led to identification several novel microdeletion and microduplication syndromes. Methods: Owing to the national array-CGH network funded by the French Ministry of Health, shared information about patients with rare disease helped to define critical intervals and evaluate their gene content, and finally determine the phenotypic consequences of genomic array findings. Results: In this study, nine unrelated patients with overlapping de novo interstitial microdeletions involving 4q21 are reported. Several major features are common to all patients, including neonatal muscular hypotonia, severe psychomotor retardation, marked progressive growth restriction, distinctive facial features and absent or severely delayed speech. The boundaries and the sizes of the nine deletions are different, but an overlapping region of 1.37 Mb is defined; this region contains five RefSeq genes: PRKG2, RASGEF1B, HNRNPD, HNRPDL and ENOPH1. Discussion: Adding new individuals with similar clinical features and 4q21 deletion allowed us to reduce the critical genomic region encompassing two genes, PRKG2 and RASGEF1B. PRKG2 encodes cGMP-dependent protein kinase type II, which is expressed in brain and in cartilage. Information from genetically modified animal models is pertinent to the clinical phenotype. RASGEF1B is a guanine nucleotide exchange factor for Ras family proteins, and several members have been reported as key regulators of actin and microtubule dynamics during both dendrite and spine structural plasticity. Conclusion: Clinical and molecular delineation of 4q21 deletion supports a novel microdeletion syndrome and suggests a major contribution of PRKG2 and RASGEF1B haploinsufficiency to the core phenotype.

Masurel-Paulet A.,Center de Genetique et Center de Reference Anomalies du developpement et syndromes malformatifs | Andrieux J.,Laboratoire Of Genetique Medicale | Callier P.,Service de Cytogenetique | Cuisset J.M.,Service de Neuropediatrie | And 29 more authors.
Clinical Genetics | Year: 2010

The increasing use of array-comparative genomic hybridization (array-CGH) to identify copy number variations (CNVs) in patients with developmental delay (DD), mental retardation and/or dysmorphic features has allowed the recent recognition of numerous genomic imbalances, including the 15q13.3 microdeletion. Patients with this microdeletion generally present with relatively consistent breakpoints at BP4 and BP5, which include the CHRNA7 gene. About 100 index cases have been reported since the first publication in 2008. This large number of patients ascertained through highly variable samples has been necessary to describe the full phenotypic spectrum of this microdeletion, ranging from mental retardation with dysmorphic features, epilepsy, neuropsychiatric disturbances with or without cognitive impairment to complete absence of anomalies. Here, we describe a collaborative study reporting a new cohort of 12 index patients and 13 relatives carrying a heterozygous BP4-BP5 microdeletion out of a series of 4625 patients screened by array-CGH for DD. We confirm the clinical expressivity of the disease as well as the incomplete penetrance in seven families. We showed through a review of the literature that males are more likely to be symptomatic. Sequence analysis of CHRNA7 yielded no data to support the unmasking of recessive variants as a cause of phenotypic variability. We also report the first patient carrying a 15q13.3 homozygous microdeletion inherited from both parents. He had severe epileptic encephalopathy with retinopathy, autistic features and choreoathetosis. Besides the classical ~1.5 Mb BP4-BP5 microdeletion, we also describe three index patients and two relatives with a smaller 500 kb microdeletion, including the CHRNA7 gene. © 2010 John Wiley & Sons A/S.

Redin C.,University of Strasbourg | Le Gras S.,Microarrays and Sequencing Platform | Mhamdi O.,University of Tunis | Geoffroy V.,Bioinformatics Platform | And 17 more authors.
Journal of Medical Genetics | Year: 2012

Background: Bardet-Biedl syndrome (BBS) is a pleiotropic recessive disorder that belongs to the rapidly growing family of ciliopathies. It shares phenotypic traits with other ciliopathies, such as Alström syndrome (ALMS), nephronophthisis (NPHP) or Joubert syndrome. BBS mutations have been detected in 16 different genes (BBS1-BBS16) without clear genotypeto-phenotype correlation. This extensive genetic heterogeneity is a major concern for molecular diagnosis and genetic counselling. While various strategies have been recently proposed to optimise mutation detection, they either fail to detect mutations in a majority of patients or are time consuming and costly. Method: We tested a targeted exon-capture strategy coupled with multiplexing and high-throughput sequencing on 52 patients: 14 with known mutations as proof-of-principle and 38 with no previously detected mutation. Thirty genes were targeted in total including the 16 BBS genes, the 12 known NPHP genes, the single ALMS gene ALMS1 and the proposed modifier CCDC28B. Results: This strategy allowed the reliable detection of causative mutations (including homozygous/ heterozygous exon deletions) in 68% of BBS patients without previous molecular diagnosis and in all proof-ofprinciple samples. Three probands carried homozygous truncating mutations in ALMS1 confirming the major phenotypic overlap between both disorders. The efficiency of detecting mutations in patients was positively correlated with their compliance with the classical BBS phenotype (mutations were identified in 81% of 'classical' BBS patients) suggesting that only a few true BBS genes remain to be identified. We illustrate some interpretation problems encountered due to the multiplicity of identified variants. Conclusion This strategy is highly efficient and cost effective for diseases with high genetic heterogeneity, and guarantees a quality of coverage in coding sequences of target genes suited for diagnosis purposes.

Roll P.,French Institute of Health and Medical Research | Roll P.,Aix - Marseille University | Sanlaville D.,Service de Cytogenetique Constitutionnelle | Sanlaville D.,University of Lyon | And 23 more authors.
PLoS ONE | Year: 2010

Background: Benign infantile convulsions and paroxysmal dyskinesia are episodic cerebral disorders that can share common genetic bases. They can be co-inherited as one single autosomal dominant trait (ICCA syndrome); the disease ICCA gene maps at chromosome 16p12-q12. Despite intensive and conventional mutation screening, the ICCA gene remains unknown to date. The critical area displays highly complicated genomic architecture and is the site of deletions and duplications associated with various diseases. The possibility that the ICCA syndrome is related to the existence of large-scale genomic alterations was addressed in the present study. Methodology/Principal Findings: A combination of whole genome and dedicated oligonucleotide array comparative genomic hybridization coupled with quantitative polymerase chain reaction was used. Low copy number of a region corresponding to a genomic variant (Variation_7105) located at 16p11 nearby the centromere was detected with statistical significance at much higher frequency in patients from ICCA families than in ethnically matched controls. The genomic variant showed no apparent difference in size and copy number between patients and controls, making it very unlikely that the genomic alteration detected here is ICCA-specific. Furthermore, no other genomic alteration that would directly cause the ICCA syndrome in those nine families was detected in the ICCA critical area. Conclusions/Significance: Our data excluded that inherited genomic deletion or duplication events directly cause the ICCA syndrome; rather, they help narrowing down the critical ICCA region dramatically and indicate that the disease ICCA genetic defect lies very close to or within Variation_7105 and hence should now be searched in the corresponding genomic area and its surrounding regions. © 2010 Roll et al.

Keren B.,Hopital de la Pitie Salpetriere | Schluth-Bolard C.,Service de cytogenetique constitutionnelle | Egea G.,Service de cytogenetique constitutionnelle | Sanlaville D.,Service de cytogenetique constitutionnelle
Archives de Pediatrie | Year: 2010

Human genome consists of 23 pairs of chromosomes, bearing our genetic information. Basically, there are two main approaches to analyse our genome: molecular genetics with direct sequencing, which detects genic mutations, and cytogenetics with the karyotype, which detects number and structural chromosomal anomalies. The main limitation of the karyotype is its level of resolution: it cannot detect abnormalities smaller than five megabases. The combined use of cytogenetics and molecular genetics has allowed the development of several new techniques that provide a comprehensive analysis of the genome with a very high level of resolution. Currently, the most efficient of those techniques is comparative genomic hybridization on microarray (array CGH), which already has diagnostic applications. However, those new methods are challenging to interpret and they raise ethical problems. Therefore they must be cautiously supervised. © 2010 Elsevier Masson SAS.

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