Targeted exome sequencing for mitochondrial disorders reveals high genetic heterogeneity

Abstract

BackgroundMitochondrial disorders are difficult to diagnose due to extreme genetic and phenotypic heterogeneities.MethodsWe explored the utility of targeted next-generation sequencing for the diagnosis of mitochondrial disorders in 148 patients submitted for clinical testing. A panel of 447 nuclear genes encoding mitochondrial respiratory chain complexes, and other genes inducing secondary mitochondrial dysfunction or that cause diseases which mimic mitochondrial disorders were tested.ResultsWe identified variants considered to be possibly disease-causing based on family segregation data and/or variants already known to cause disease in twelve genes in thirteen patients. Rare or novel variants of unknown significance were identified in 45 additional genes for various metabolic, genetic or neurogenetic disorders.ConclusionsPrimary mitochondrial defects were confirmed only in four patients indicating that majority of patients with suspected mitochondrial disorders are presumably not the result of direct impairment of energy production. Our results support that clinical and routine laboratory ascertainment for mitochondrial disorders are challenging due to significant overlapping non-specific clinical symptoms and lack of specific biomarkers. While next-generation sequencing shows promise for diagnosing suspected mitochondrial disorders, the challenges remain as the underlying genetic heterogeneity may be greater than suspected and it is further confounded by the similarity of symptoms with other conditions as we report here.

Utility of next generation sequencing in genetic diagnosis of early onset neuromuscular disorders

“…We designed the NGS test to include all genes implicated in NMDs, focusing in particular on hereditary myopathies. This choice was based on the observation that both clinical and laboratory diagnosis of heterogeneous genetic conditions, even if performed by experienced physicians and pathologists, is often extremely challenging due to overlapping clinical phenotypes, expanded clinical spectrums, difficulties to obtain a muscle biopsy, and the complexity of performing and interpreting immunohistochemical stains 12 13…”

“…PolyPhen-2 and SIFT (sorting intolerant from tolerant) scores were used only for reference but were not used for filtering the variants. For variants in genes with autosomal dominant and X-linked disease inheritance, we used the minor allele frequency (MAF) cut-off of 0.2%, and for variants in genes with autosomal recessive disease inheritance, we used the MAF cut-off of 0.5% 13. Variants that exceeded these frequencies were not considered as potential mutations, even if they were previously reported as such in the Human Gene Mutation Database (HGMD).…”

Molecular diagnosis of glycogen storage disease and disorders with overlapping clinical symptoms by massive parallel sequencing

“…4 This very cost-effective technology is particularly appropriate for screening for mutations in disorders with highly heterogeneous genetic backgrounds, such as GSD, congenital disorder of glycosylation, lysosomal disorders, and mitochondrial disorders [5][6][7][8] In addition, its ability to detect mutations in large genes and to identify copy number variations is very advantageous. The implementation of massive parallel sequencing has begun to revolutionize the field of genetic diagnosis.…”

Molecular diagnosis of coenzyme Q10deficiency

“…On the other hand, targeted resequencing using gene panel is appearing in a clinical setting due to lower sequencing costs, shorter sequencing time, simpler data analysis and greater sensitivity per gene due to the greater coverage achieved [35]. These new approaches may be ideal for diagnosis of several disorders with broad heterogenic phenotypes and genotypes [31,32], such as the mitochondrial disorders and CoQ deficiency syndromes.…”

“…These technologies are now widely used for research purposes and are starting to find their way into clinical applications [31,32]. Whole genome and exome sequencing approaches are being successfully implemented in research projects [33,34], but are not yet routine strategies in diagnosis due to high costs, long turnover times (run and analysis time) and ethical issues.…”