Mitochondrial DNA Analysis
Mitochondrial DNA analysis for known pathogenic mitochondrial variants is available with a Claritas Clinical Exome order at no additional charge, and should be considered when a mitochondrial disorder is suspected in the setting of a “complex” phenotype.
Mitochondrial disorders can present with a variety of symptoms, and it can be difficult to establish a clinical diagnosis for several reasons:
- Multiple organ systems can be involved to varying degrees and therefore symptoms vary from one patient to another.
- Age of onset varies among patients; persons do not fit into one particular category.
- Symptoms do not differentiate between patients affected by a mtDNA vs. a nucDNA variant.
- Cellular “burden” of variants varies with mtDNA due to heteroplasmy (the proportion of mitochondrial organelles affected by a mtDNA variant may vary by tissue type within the same individual).
- Mitochondrial genome and exome are sequenced simultaneously by deep NGS sequencing. The average sequencing depth for the mitochondrial genome is >200x with >90% of DNA positions covered at >100x.
- >99% analytical sensitivity for 10% heteroplasmy.
- Nuclear DNA is selected by both hybridization capture and short amplicon amplification while mitochondrial DNA is initially sequenced via hybridization capture and variants confirmed using long range PCR to eliminate nuMT sequence variants.
- Two independent sets of long range PCR amplicons are used for redundant confirmation of low-level heteroplasmy.
- Confirmation of identified known pathogenic variants is performed by an orthogonal method.
- Sanger fill-in of relevant low coverage gene regions upon request.
This test cannot currently be ordered as an independent assay; it must be ordered in conjunction with the Claritas Clinical Exome. A stand-alone assay is in development, with an anticipated launch in the second half of 2017.