Mitochondrial DNA Depletion Syndrome Panel

Last modified: Jun 12, 2018

Summary

  • Is a 25 gene panel that includes assessment of non-coding variants
  • Is ideal for patients with a clinical suspicion of mitochondrial DNA depletion syndrome. The genes on this panel are included in the Comprehensive Metabolism Panel.

Analysis methods

  • PLUS
  • SEQ
  • DEL/DUP

Availability

4 weeks

Number of genes

25

Test code

ME0201

Panel size

Small

CPT codes

SEQ 81404
SEQ 81405
SEQ 81406
DEL/DUP 81479

Summary

The Blueprint Genetics Mitochondrial DNA Depletion Syndrome Panel (test code ME0201):

  • Is a 25 gene panel that includes assessment of selected non-coding disease-causing variants
  • Is available as PLUS analysis (sequencing analysis and deletion/duplication analysis), sequencing analysis only or deletion/duplication analysis only

ICD codes

Commonly used ICD-10 code(s) when ordering the Mitochondrial DNA Depletion Syndrome Panel

ICD-10 Disease
G71.3 Mitochondrial DNA depletion syndrome

Sample Requirements

  • EDTA blood, min. 1 ml
  • Purified DNA, min. 3μg
  • Saliva (Oragene DNA OG-500 kit)

Label the sample tube with your patient’s name, date of birth and the date of sample collection.

Note that we do not accept DNA samples isolated from formalin-fixed paraffin-embedded (FFPE) tissue.

Mitochondrial DNA depletion syndrome (MDS) refers to a group of disorders which cause the affected tissues to suffer from a significant drop in mitochondrial DNA. Symptoms may manifest as myopathic (mutations in TK2, RRM2B and AG), encephalomyopathic (SUCLA2, SUCLG1, and RRM2B) hepatocerebral (DGUOK, MPV17, POLG and C10ORF2), and/or neurogastrointestinal (TYMP). These syndromes affect tissue found in the muscle, liver, or both the muscle and brain, respectively. Typically, the condition is fatal in infancy or early childhood. However some patients have survived into puberty with a myopathic variant and some into adulthood with a SUCLA2 encephalomyopathic variant. There are some preliminary treatments that have shown to reduce symptoms but currently no curative treatment for any form of MDSs is available. Nuclear encoded genes associated with multiple mtDNA deletions or mtDNA depletion include POLG, POLG2, C10orf2, SLC25A4 (autosomal progressive external ophthalmoplegia), TYMP (mitochondrial neurogastrointestinal encephalomyopathy), POLG (Alpers-Huttenlocher syndrome), POLG, C10orf2, OPA1 (ataxia neuropathy syndromes 2), TK2 (infantile myopathy / spinal muscular atrophy), DGUOK (encephalomyopathy and liver failure), SUCLA2 (hypotonia, movement disorder, and/or Leigh syndrome with methylmalonic aciduria) and RRM2B (hypotonia, encephalopathy, renal tubulopathy, lactic acidosis).

Genes in the Mitochondrial DNA Depletion Syndrome Panel and their clinical significance

Gene Associated phenotypes Inheritance ClinVar HGMD
AGK* Sengers syndrome, Cataract 38 AR 18 27
APTX Ataxia, early-onset, with oculomotor apraxia and hypoalbuminemia AR 14 42
AUH 3-methylglutaconic aciduria AR 13 11
C10ORF2 Perrault syndrome, Mitochondrial DNA depletion syndrome, Progressive external ophthalmoplegia with mitochondrial DNA deletions, autosomal dominant, 3 AR 36 77
C12ORF65 Spastic paraplegia, Combined oxidative phosphorylation deficiency AR 10 11
DGUOK Mitochondrial DNA depletion syndrome, Portal hypertension, noncirrhotic, Progressive external ophthalmoplegia with mitochondrial DNA deletions, autosomal recessive 4 AR 23 62
FBXL4 Mitochondrial DNA depletion syndrome AR 55 47
MFN2 Hereditary motor and sensory neuropathy, Charcot-Marie-Tooth disease AD/AR 59 220
MPV17 Mitochondrial DNA depletion syndrome AR 35 42
NDUFS1 Mitochondrial complex I deficiency AR 22 27
OPA1 Optic atrophy, Optic atrophy 1, Optic atrophy with or without deafness, Ophthalmoplegia, myopathy, ataxia, and neuropathy, Behr synrome, Mitochondrial DNA depletion syndrome 14 AD/AR 97 387
OPA3 Optic atrophy, 3-methylglutaconic aciduria AD/AR 9 15
POLG POLG-related ataxia neuropathy spectrum disorders, Sensory ataxia, dysarthria, and ophthalmoparesis, Alpers syndrome, Progressive external ophthalmoplegia with mitochondrial DNA deletions, Mitochondrial DNA depletion syndrome AD/AR 90 280
POLG2 Progressive external ophthalmoplegia with mitochondrial DNA deletions AD 5 13
RRM2B Progressive external ophthalmoplegia with mitochondrial DNA deletions, Mitochondrial DNA depletion syndrome AD/AR 42 41
SLC25A3 Micochondrial phosphate carrier deficiency AR 2 5
SLC25A4 Progressive external ophthalmoplegia with mitochondrial DNA deletions, Mitochondrial DNA depletion syndrome AD/AR 12 15
SPG7 Spastic paraplegia AR 64 108
SUCLA2 Mitochondrial DNA depletion syndrome AR 9 27
SUCLG1 Mitochondrial DNA depletion syndrome AR 11 28
TIMM8A* Mohr-Tranebjaerg syndrome, Jensen syndrome, Opticoacoustic nerve atrophy with dementia XL 10 21
TK2 Mitochondrial DNA depletion syndrome AR 38 45
TMEM126A Optic atrophy AR 2 1
TYMP Mitochondrial DNA depletion syndrome AR 85 94
WFS1 Wolfram syndrome, Deafness, Wolfram-like syndrome, autosomal dominant, Deafness, autosomal dominant 6/14/38, Cataract 41 AD/AR 68 351

* Some, or all, of the gene is duplicated in the genome. Read more.

# The gene has suboptimal coverage (means <90% of the gene’s target nucleotides are covered at >20x with mapping quality score (MQ>20) reads).

The sensitivity to detect variants may be limited in genes marked with an asterisk (*) or number sign (#)

Gene refers to the HGNC approved gene symbol; Inheritance refers to inheritance patterns such as autosomal dominant (AD), autosomal recessive (AR), X-linked (XL), X-linked dominant (XLD) and X-linked recessive (XLR); ClinVar refers to the number of variants in the gene classified as pathogenic or likely pathogenic in this database (ClinVar); HGMD refers to the number of variants with possible disease association in the gene listed in Human Gene Mutation Database (HGMD). The list of associated, gene specific phenotypes are generated from CGD or Orphanet databases.

Non-coding variants covered by the panel

Gene Genomic location HG19 HGVS RefSeq RS-number
DGUOK Chr2:74177701 c.444-11C>G NM_080916.2 rs536746349
DGUOK Chr2:74177650 c.444-62C>A NM_080916.2
OPA1 Chr3:193374829 c.2179-40G>C NM_130837.2
OPA1 Chr3:193335986 c.610+360G>A NM_130837.2
OPA1 Chr3:193335990 c.610+364G>A NM_130837.2
TIMM8A ChrX:100601671 c.133-23A>C NM_004085.3 rs869320666
WFS1 Chr4:6271704 c.-43G>T NM_006005.3

Added and removed genes from the panel

Genes added Genes removed


Test strength

The strengths of this test include:
  • CAP and ISO-15189 accreditations covering all operations at Blueprint Genetics including all Whole Exome Sequencing, NGS panels and confirmatory testing
  • CLIA-certified personnel performing clinical testing in a CLIA-certified laboratory
  • Powerful sequencing technologies, advanced target enrichment methods and precision bioinformatics pipelines ensure superior analytical performance
  • Careful construction of clinically effective and scientifically justified gene panels
  • Our Nucleus online portal providing transparent and easy access to quality and performance data at the patient level
  • Our publically available analytic validation demonstrating complete details of test performance
  • ~1,500 non-coding disease causing variants in Blueprint WES assay (please see below ‘Non-coding disease causing variants covered by this panel’)
  • Our rigorous variant classification based on modified ACMG variant classification scheme
  • Our systematic clinical interpretation workflow using proprietary software enabling accurate and traceable processing of NGS data
  • Our comprehensive clinical statements

Test limitations

Genes with partial, or whole gene, segmental duplications in the human genome are marked with an asterisk (*) if they overlap with the UCSC pseudogene regions. The technology may have limited sensitivity to detect variants in genes marked with these symbols (please see the Panel content table above).

This test does not detect the following:
  • Complex inversions
  • Gene conversions
  • Balanced translocations
  • Mitochondrial DNA variants
  • Repeat expansion disorders unless specifically mentioned
  • Non-coding variants deeper than ±20 base pairs from exon-intron boundary unless otherwise indicated (please see above Panel Content / non-coding variants covered by the panel).

This test may not reliably detect the following:

  • Low level mosaicism (variant with a minor allele fraction of 14.6% is detected with 90% probability)
  • Stretches of mononucleotide repeats
  • Indels larger than 50bp
  • Single exon deletions or duplications
  • Variants within pseudogene regions/duplicated segments

The sensitivity of this test may be reduced if DNA is extracted by a laboratory other than Blueprint Genetics.

For additional information, please refer to the Test performance section and see our Analytic Validation.

The Blueprint Genetics mitochondrial DNA depletion syndrome panel covers classical genes associated with mitochondrial DNA depletion syndrome. The genes on the panel have been carefully selected based on scientific literature, mutation databases and our experience.

Our panels are sliced from our high-quality whole exome sequencing data. Please see our sequencing and detection performance table for different types of alterations at the whole exome level (Table).

Assays have been validated for different starting materials including EDTA-blood, isolated DNA (no FFPE), saliva and dry blood spots (filter card) and all provide high-quality results. The diagnostic yield varies substantially depending on the assay used, referring healthcare professional, hospital and country. Blueprint Genetics' Plus Analysis (Seq+Del/Dup) maximizes the chance to find a molecular genetic diagnosis for your patient although Sequence Analysis or Del/Dup Analysis may be a cost-effective first line test if your patient's phenotype is suggestive of a specific mutation type.

Performance of Blueprint Genetics Whole Exome Sequencing (WES) assay. All individual panels are sliced from WES data.

Sensitivity % (TP/(TP+FN) Specificity %
Single nucleotide variants 99.65% (412,456/413,893) >99.99%
Insertions, deletions and indels by sequence analysis
1-10 bps 96.94% (17,070/17,608) >99.99%
11-50 bps 99.07% (957/966) >99.99%
Copy number variants (exon level dels/dups)
Clinical samples (small CNVs, n=52)
1 exon level deletion 92.3% (24/26) NA
2 exons level deletion/duplication 100.0% (11/11) NA
3-7 exons level deletion/duplication 93.3% (14/15) NA
Microdeletion/-duplication sdrs (large CNVs, n=37))
Size range (0.1-47 Mb) 100% (37/37)
Simulated CNV detection
2 exons level deletion/duplication 90.98% (7,357/8,086) 99.96%
5 exons level deletion/duplication 98.63% (7,975/8,086) 99.98%
     
The performance presented above reached by WES with the following coverage metrics
     
Mean sequencing depth at exome level 174x
Nucleotides with >20x sequencing coverage (%) 99.4%

Bioinformatics

The target region for each gene includes coding exons and ±20 base pairs from the exon-intron boundary. In addition, the panel includes non-coding variants if listed above (Non-coding variants covered by the panel). Some regions of the gene(s) may be removed from the panel if specifically mentioned in the ‘Test limitations” section above. The sequencing data generated in our laboratory is analyzed with our proprietary data analysis and annotation pipeline, integrating state-of-the art algorithms and industry-standard software solutions. Incorporation of rigorous quality control steps throughout the workflow of the pipeline ensures the consistency, validity and accuracy of results. Our pipeline is streamlined to maximize sensitivity without sacrificing specificity. We have incorporated a number of reference population databases and mutation databases such as, but not limited, to 1000 Genomes Project, gnomAD, ClinVar and HGMD into our clinical interpretation software to make the process effective and efficient. For missense variants, in silico variant prediction tools such as SIFT, PolyPhen, MutationTaster are used to assist with variant classification. Through our online ordering and statement reporting system, Nucleus, the customer has an access to details of the analysis, including patient specific sequencing metrics, a gene level coverage plot and a list of regions with inadequate coverage if present. This reflects our mission to build fully transparent diagnostics where customers have easy access to crucial details of the analysis process.

Clinical interpretation

We provide customers with the most comprehensive clinical report available on the market. Clinical interpretation requires a fundamental understanding of clinical genetics and genetic principles. At Blueprint Genetics, our PhD molecular geneticists, medical geneticists and clinical consultants prepare the clinical statement together by evaluating the identified variants in the context of the phenotypic information provided in the requisition form. Our goal is to provide clinically meaningful statements that are understandable for all medical professionals regardless of whether they have formal training in genetics.

Variant classification is the corner stone of clinical interpretation and resulting patient management decisions. Our classifications follow the Blueprint Genetics Variant Classification Schemes based on the ACMG guideline 2015. Minor modifications were made to increase reproducibility of the variant classification and improve the clinical validity of the report. Our experience with tens of thousands of clinical cases analyzed at our laboratory allowed us to further develop the industry standard.

The final step in the analysis of sequence variants is confirmation of variants classified as pathogenic or likely pathogenic using bi-directional Sanger sequencing. Variant(s) fulfilling all of the following criteria are not Sanger confirmed: 1) the variant quality score is above the internal threshold for a true positive call, 2) an unambiguous IGV in-line with the variant call and 3) previous Sanger confirmation of the same variant at least three times at Blueprint Genetics. Reported variants of uncertain significance are confirmed with bi-directional Sanger sequencing only if the quality score is below our internally defined quality score for true positive call. Reported copy number variations with a size <10 exons are confirmed by orthogonal methods such as qPCR if the specific CNV has been seen less than three times at Blueprint Genetics.

Our clinical statement includes tables for sequencing and copy number variants that include basic variant information (genomic coordinates, HGVS nomenclature, zygosity, allele frequencies, in silico predictions, OMIM phenotypes and classification of the variant). In addition, the statement includes detailed descriptions of the variant, gene and phenotype(s) including the role of the specific gene in human disease, the mutation profile, information about the gene’s variation in population cohorts and detailed information about related phenotypes. We also provide links to the references used, congress abstracts and mutation databases to help our customers further evaluate the reported findings if desired. The conclusion summarizes all of the existing information and provides our rationale for the classification of the variant.

Identification of pathogenic or likely pathogenic variants in dominant disorders or their combinations in different alleles in recessive disorders are considered molecular confirmation of the clinical diagnosis. In these cases, family member testing can be used for risk stratification within the family. In the case of variants of uncertain significance (VUS), we do not recommend family member risk stratification based on the VUS result. Furthermore, in the case of VUS, we do not recommend the use of genetic information in patient management or genetic counseling.

Our interpretation team analyzes millions of variants from thousands of individuals with rare diseases. Thus, our database, and our understanding of variants and related phenotypes, is growing by leaps and bounds. Our laboratory is therefore well positioned to re-classify previously reported variants as new information becomes available. If a variant previously reported by Blueprint Genetics is re-classified, our laboratory will issue a follow-up statement to the original ordering health care provider at no additional cost.