Corinne Bareil

Autosomal recessive retinal dystrophy associated with two novel mutations in the RPE65 gene.

Retinal dystrophies are a complex set of hereditary diseases of the retina that result in the degeneration of photoreceptors. Recent studies have shown that mutations in RPE65, a gene that codes for a retinal pigment epithelium (RPE)-specific protein thought to be involved in the 11-cis-retinoid metabolism, a key process in vision, cause severe, early onset retinal dystrophy. We describe two novel missense RPE65 mutations, L22P and H68Y, in a compound heterozygote with autosomal recessive retinal dystrophy. The relatively mild phenotype associated with these mutations suggests a possible link between the severity of the disease and the type of mutations in the RPE65 gene.

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.

Four novel dystrophin point mutations: detection by protein truncation test and transcript analysis in lymphocytes from Duchenne muscular dystrophy patients.

About 30% of cases of Duchenne muscular dystrophy (DMD) result from point mutations randomly distributed in the immense dystrophin gene. As already observed for the gross rearrangements, most of the DMD point mutations identified so far give rise to truncated proteins. Here, we report results of a comprehensive search for point mutations within the dystrophin gene based on illegitimate transcript analysis by using the RT-PCR technique in combination with a method capable of selectively detecting translation-termination mutations, called the protein truncation test (PTT). The RT-PCR-PTT procedure was successful in detecting mutations in 4 out of the 6 DMD patients who were investigated. These mutations, Q2972X in exon 59, 3474insC in exon 24, delT393-G394+5 in exon/intron 3, and 2436delAG in exon 18, had not been previously described. Moreover, several alternatively spliced forms of ectopic dystrophin mRNA were characterized in normal controls or in DMD patients. Most of these differentially spliced messages consisting of exon skipping or intronic sequence insertion are reported here for the first time.

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.

A Classification Model Relative to Splicing for Variants of Unknown Clinical Significance: Application to the CFTR Gene

Molecular diagnosis of cystic fibrosis and cystic fibrosis transmembrane regulator (CFTR)‐related disorders led to the worldwide identification of nearly 1,900 sequence variations in the CFTR gene that consist mainly of private point mutations and small insertions/deletions. Establishing their effect on the function of the encoded protein and therefore their involvement in the disease is still challenging and directly impacts genetic counseling. In this context, we built a decision tree following the international guidelines for the classification of variants of unknown clinical significance (VUCS) in the CFTR gene specifically focused on their consequences on splicing. We applied general and specific criteria, including comprehensive review of literature and databases, familial genetics data, and thorough in silico studies. This model was tested on 15 intronic and exonic VUCS identified in our cohort. Six variants were classified as probably nonpathogenic considering their impact on splicing and eight as probably pathogenic, which include two apparent missense mutations. We assessed the validity of our method by performing minigenes studies and confirmed that 93% (14/15) were correctly classified. We provide in this study a high‐performance method that can play a full role in interpreting the results of molecular diagnosis in emergency context, when functional studies are not achievable.

New multiplex PCR-based protocol allowing indirect diagnosis of FSHD on single cells: can PGD be offered despite high risk of recombination?

Molecular pathophysiology of facioscapulohumeral muscular dystrophy (FSHD) involves the heterozygous contraction of the number of tandemly repeated D4Z4 units at chromosome 4q35.2. FSHD is associated with a range of 1–10 D4Z4 units instead of 11–150 in normal controls. Several factors complicate FSHD molecular diagnosis, especially the cis-segregation of D4Z4 contraction with a 4qA allele, whereas D4Z4 shortening is silent both on alleles 4qB and 10q. Discrimination of pathogenic 4q-D4Z4 alleles from highly homologous 10q-D4Z4 arrays requires the use of the conventional Southern blot, which is not suitable at the single-cell level. Preimplantation genetic diagnosis (PGD) is a frequent request from FSHD families with several affected relatives. We aimed to develop a rapid and sensitive PCR-based multiplex approach on single cells to perform an indirect familial segregation study of pathogenic alleles. Among several available polymorphic markers at 4q35.2, the four most proximal (D4S2390, D4S1652, D4S2930 and D4S1523, <1.23 Mb) showing the highest heterozygote frequencies (67–91%) were selected. Five recombination events in the D4S2390-D4S1523 interval were observed among 144 meioses. In the D4S2390-D4Z4 interval, no recombination event occurred among 28 FSHD meioses. Instead, a particular haplotype segregated with both clinical and molecular status, allowing the characterization of an at-risk allele in each tested FSHD family (maximal LOD score 2.98 for θ=0.0). This indirect protocol can easily complement conventional techniques in prenatal diagnosis. Although our multiplex PCR-based approach technically fulfils guidelines for single-cell analysis, the relatively high recombination risk hampers its application to PGD.

Non-invasive prenatal diagnosis of monogenic disorders: an optimized protocol using MEMO qPCR with miniSTR as internal control

Abstract Background: Analysis of circulating cell-free fetal DNA (cffDNA) in maternal plasma is very promising for early diagnosis of monogenic diseases. However, this approach is not yet available for routine use and remains technically challenging because of the low concentration of cffDNA, which is swamped by the overwhelming maternal DNA. Methods: To make clinical applications more readily accessible, we propose a new approach based on mutant enrichment with 3′-modified oligonucleotides (MEMO) PCR along with real-time PCR to selectively amplify from the maternal blood the paternally inherited fetal allele that is not present in the maternal genome. Results: The first proof of concept of this strategy was displayed for cystic fibrosis by the accuracy of our detection of the p.Gly542* mutation used as the initial developmental model. Subsequently, a retrospective study of plasmas originating from two pregnant women carrying a fetus with private mutation confirmed the effectiveness of our method. We confirmed the presence of cffDNA in the studied samples by the identification of a tri-allelic DNA profile using a miniSTR kit. Conclusions: This new non-invasive prenatal diagnosis test offers numerous advantages over current methods: it is simple, cost effective, time efficient and does not require complex equipment or bioinformatics settings. Moreover, our assays for different private mutations demonstrate the viability of this approach in clinical settings for monogenic disorders.

Different Mutations in RPE65 Are Associated with Variability in the Severity of Retinal Dystrophy

RPE65 encodes a retinal pigment epithelium (RPE)-specific protein thought to be involved in the 11 -cis retinoid metabolism, a key process in vision.To evaluate the visual implications of defects in this gene, we screened patients with various types of inherited retinal dystrophies. We found two nonsense mutations, 1121delA and R234X, in two sibs with Leber’s congenital amaurosis. The presence of either one of the two mutations on each allele indicates that they were compound heterozygotes. In a subsequent screening, two missense mutations, L22P and H68Y, were found in a patient with autosomal recessive retinitis pigmentosa.This individual was also a compound heterozygote. These results suggest that the level of impairment of the RPE65 protein, presumably abnormal activity in the case of amino acid substitutions and absence of protein in the case of null mutations, controls the rate at which the photoreceptors degenerate, and hence the severity of the phenotype.

Banques de données de mutations : enjeux et perspectives pour les maladies génétiques orphelines

New technologies, which constantly become available for mutation detection and gene analysis, have contributed to an exponential rate of discovery of disease genes and variation in the human genome. The task of collecting and documenting this enormous amount of data in genetic databases represents a major challenge for the future of biological and medical science. The Locus Specific Databases (LSDBs) are so far the most efficient mutation databases. This review presents the main types of databases available for the analysis of mutations responsible for genetic disorders, as well as open perspectives for new therapeutic research or challenges for future medicine. Accurate and exhaustive collection of variations in human genomes will be crucial for research and personalized delivery of healthcare.

4 Valuable collaboration between a molecular CFTR database and a national CF registry: the French experience

4 Valuable collaboration between a molecular CFTR database and a national CF registry: the French experience C. Bareil, L. Lemonnier, C. Dehillotte, V. Colomb-Jung, C. Theze, M.-P. Audrezet, C. Ferec, T. Bienvenu, E. Girodon, P. Fanen, C. Mekki, E. Bieth, V. Gaston, P. Fergelot, M.-P. Reboul, A. Kitzis, G. Lalau, A. Pagin, M.-C. Malinge, C. Raynal, M. Claustres. CHRU de Montpellier, Laboratoire de Genetique Moleculaire, Montpellier, France; Association Vaincre La Mucoviscidose, Paris, France; CHRU Brest, Laboratoire de Genetique Moleculaire, Brest, France; Hopital Cochin, APHP, Service de Genetique et Biologie Moleculaires, Paris, France; GH Henri Mondor, Departement de Genetique, Creteil, France; CHRU de Toulouse, Service de Genetique Medicale, Toulouse, France; Hopital Pellegrin – CHU de Bordeaux, Laboratoire de Genetique Moleculaire, Bordeaux, France; CHU de Poitiers, Service de Genetique, Poitiers, France; CHRU de Lille, Service de Toxicologie et Genopathies, Lille, France; CHU Angers, UF de Genetique Moleculaire – Departement de Biochimie Genetique, Angers, France In 2013 the French CF Registry and CFTR-France database managers started collaborating to address the limitations of each base, due to the lack of genetics and clinical data cross comparison. The aim was to check and update clinical data in CFTR-France and genetic data in the Registry. Records from the two databases were compared using name, date of birth, gender, sex and mutations. Matched and unmatched records were identified. Discrepancies were checked and confirmed by the laboratories and then sent to the CF centres. Comparison of 8807 patients in the Registry and 4617 in CFTR-France identified 1924 full match and 321 partially matched records. Molecular laboratories confirmations added 216 full matches. The remaining 105 patients still need confirmation by laboratories and CF centres. Among the 321 patients, personal data and/or genotype discrepancies were identified for respectively 70 and 129 patients. This database crossing allowed 110 genotypes to be corrected/completed in the Registry, which is of major interest. Indeed, if those incorrect data are also present in the CF centre medical files, they can impact familial genetic counselling and impair patients’ access to optimal mutation targeted therapies. Clinical data provided by the Registry are currently being analysed to complete the CFTR-France phenotypic status of patients. In-depth analysis of these data allows patients to be re-classified in different phenotypic groups (CF, CBAVD, isolated bronchiectasis or pancreatitis) and genotype/phenotype relationships to be refined, in order to better manage rare variants interpretation, medical care strategy and genetic counselling to families.