Targeted next generation sequencing with an extended gene panel does not impact variant detection in mitochondrial diseases

Abstract Background Since the advent of next generation sequencing (NGS), several studies have tried to evaluate the relevance of targeted gene panel sequencing and whole exome sequencing for molecular diagnosis of mitochondrial diseases. The comparison between these different strategies is extremely difficult. A recent study analysed a cohort of patients affected by a mitochondrial disease using a NGS approach based on a targeted gene panel including 132 genes. This strategy led to identify the causative mutations in 15.2% of cases. The number of novel genes responsible for respiratory chain deficiency increases very rapidly. Methods In order to determine the impact of larger panels used as a first screening strategy on molecular diagnosis success, we analysed a cohort of 80 patients affected by a mitochondrial disease with a first mitochondrial DNA (mtDNA) NGS screening and secondarily a targeted mitochondrial panel of 281 nuclear genes. Results Pathogenic mtDNA abnormalities were identified in 4.1% (1/24) of children and 25% (14/56) of adult patients. The remaining 65 patients were analysed with our targeted mitochondrial panel and this approach enabled us to achieve an identification rate of 21.7% (5/23) in children versus 7.1% (3/42) in adults. Conclusions Our results confirm that larger gene panels do not improve diagnostic yield of mitochondrial diseases due to (i) their very high genetic heterogeneity, (ii) the ongoing discovery of novel genes and (iii) mutations in genes apparently not related to mitochondrial function that lead to secondary respiratory chain deficiency

Additional file 1: of Targeted next generation sequencing with an extended gene panel does not impact variant detection in mitochondrial diseases

Table S1. List of the genes included in the NGS panel. (PDF 7.44 kb

CHCHD10 mutations promote loss of mitochondrial cristae junctions with impaired mitochondrial genome maintenance and inhibition of apoptosis

International audienceCHCHD10-related diseases include mitochondrial DNA instability disorder, frontotemporal dementia-amyotrophic lateral sclerosis (FTD-ALS) clinical spectrum, late-onset spinal motor neuropathy (SMAJ), and Charcot-Marie-Tooth disease type 2 (CMT2). Here, we show that CHCHD10 resides with mitofilin, CHCHD3 and CHCHD6 within the "mitochondrial contact site and cristae organizing system" (MICOS) complex. CHCHD10 mutations lead to MICOS complex disassembly and loss of mitochondrial cristae with a decrease in nucleoid number and nucleoid disorganization. Repair of the mitochondrial genome after oxidative stress is impaired in CHCHD10 mutant fibroblasts and this likely explains the accumulation of deleted mtDNA molecules in patient muscle. CHCHD10 mutant fibroblasts are not defective in the delivery of mitochondria to lysosomes suggesting that impaired mitophagy does not contribute to mtDNA instability. Interestingly, the expression of CHCHD10 mutant alleles inhibits apoptosis by preventing cytochrome c release

Chromosomal microarray analysis in fetuses with an isolated congenital heart defect: A retrospective, nationwide, multicenter study in France

International audienceObjectives Congenital heart defects (CHDs) may be isolated or associated with other malformations. The use of chromosome microarray (CMA) can increase the genetic diagnostic yield for CHDs by between 4% and 10%. The objective of this study was to evaluate the value of CMA after the prenatal diagnosis of an isolated CHD. Methods In a retrospective, nationwide study performed in France, we collected data on all cases of isolated CHD that had been explored using CMAs in 2015. Results A total of 239 fetuses were included and 33 copy number variations (CNVs) were reported; 19 were considered to be pathogenic, six were variants of unknown significance, and eight were benign variants. The anomaly detection rate was 10.4% overall but ranged from 0% to 16.7% as a function of the isolated CHD in question. The known CNVs were 22q11.21 deletions (n = 10), 22q11.21 duplications (n = 2), 8p23 deletions (n = 2), an Alagille syndrome (n = 1), and a Kleefstra syndrome (n = 1). Conclusion The additional diagnostic yield was clinically significant (3.1%), even when anomalies in the 22q11.21 region were not taken into account. Hence, patients with a suspected isolated CHD and a normal karyotype must be screened for chromosome anomalies other than 22q11.21 duplications and deletions

EPHA7 haploinsufficiency is associated with a neurodevelopmental disorder

International audienceEphrin receptor and their ligands, the ephrins, are widely expressed in the developing brain. They are implicated in several developmental processes that are crucial for brain development. Deletions in genes encoding for members of the Eph/ephrin receptor family were reported in several neurodevelopmental disorders. The ephrin receptor A7 gene (EPHA7) encodes a member of ephrin receptor subfamily of the protein-tyrosine kinase family. EPHA7 plays a role in corticogenesis processes, determines brain size and shape, and is involved in development of the central nervous system. One patient only was reported so far with a de novo deletion encompassing EPHA7 in 6q16.1. We report 12 additional patients from nine unrelated pedigrees with similar deletions. The deletions were inherited in nine out of 12 patients, suggesting variable expressivity and incomplete penetrance. Four patients had tiny deletions involving only EPHA7, suggesting a critical role of EPHA7 in a neurodevelopmental disability phenotype. We provide further evidence for EPHA7 deletion as a risk factor for neurodevelopmental disorder and delineate its clinical phenotype

10q26 deletion syndrome: a French cohort study

International audience10q26 deletion syndrome (OMIM #609625) is a rare autosomal dominant genetic disorder with about 100 patients reported. Most cases are sporadic. Global development delay, short stature, microcephaly and typical facial appearance with triangular face, large forehead, low-set malformed ears, hypertelorism, prominent nose and a thin vermilion of the upper lip constitute the main clinical features. The clinical spectrum is very heterogeneous and neurobehavioral manifestations, deafness, limb malformations, cardiac and urogenital abnormalities can be associated. Thus, patients with 10q26 chromosomal deletion need multidisciplinary management strategies from birth. One of the main reasons for this heterogeneity is the variety of 10qter region chromosomal deletions summarized into the “10q26 deletion syndrome”. Various studies proposed critical regions to explain the main phenotype (Yatzenko et al., 2009; Choucair et al., 2015; Lin S et al., 2016) or more specific features (Vera-Carbonell et al., 2015; Choucair et al., 2015). In addition, these studies proposed about 20 genes of interest such as DOCK1 and FGFR2 to explain the different clinical features observed. We report a French ACLF cohort of 35 patients from 9 centers presenting 10q26 complete or partial deletions (size: 64kb to 12.5Mb), complex chromosomal rearrangement and derivative chromosomes diagnosed using DNA-array, to bring a further insight of the genotype/phenotype correlation

Whole genome paired-end sequencing elucidates functional and phenotypic consequences of balanced chromosomal rearrangement in patients with developmental disorders

International audienc