Mitochondrial Complex I Deficiency via the NDUFV1 Gene
- Summary and Pricing
- Clinical Features and Genetics
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In a review of the literature, Keone et al. noted that 17 of 130 mitochondrial complex I deficiency cases (~13%) were caused by pathogenic variants in NDUFV1 (Keone et al. 2012).
Mitochondrial complex I (CI) deficiency is characterized by a deficiency of the first and largest of the oxidative phosphorylation complexes (Fassone and Rahman 2012). Isolated mitochondrial CI deficiency is the most frequently reported childhood-onset mitochondrial disease, and may account for roughly one-third of all oxidative phosphorylation disorders (Skladal et al. 2003; Scaglia et al. 2004).
NDUFV1-associated mitochondrial CI deficiency often presents as leukodystrophy, usually accompanied by lactic acidosis in the blood and/or cerebral spinal fluid (Ortega-Recalde et al. 2013; Schuelke et al. 1999). Another common clinical presentation is Leigh syndrome (LS), a severe, progressive encephalopathy characterized by a distinct set of diagnostic criteria (Rahman and Thorburn 2015). LS symptoms include psychomotor delay or regression, isolated or combined mitochondrial complex deficiencies, elevated levels of lactate in the blood and/or cerebral spinal fluid, bilateral symmetrical lesions in the brainstem and basal ganglia, and neurologic manifestations such as hypotonia or ataxia (Lake et al. 2015; Keone et al. 2012). Leigh-like syndrome, which describes a similar clinical presentation in which one or more of these diagnostic characteristics is atypical, has also been reported in patients with pathogenic variants in NDUFV1 (Laugel et al. 2007).
Although age of onset may vary, patients with NDUFV1-related disorders generally present within the first year of life (Keone et al. 2012).
The mitochondrial respiratory chain complex I (nicotinamide adenine dinucleotide (NADH):ubiquinone oxidoreductase) is composed of at least 45 structural subunits (Fassone and Rahman 2012). 38 of these subunits are encoded by nuclear DNA, and 7 are encoded by mitochondrial DNA. The resulting holoenzyme complex plays a critical role in redox-driven proton translocation, which ultimately drives ATP synthesis within the cell (Sazanov 2015). Due to the many structural and accessory subunits required to support the assembly and function of complex I, mitochondrial CI deficiency is a genetically heterogeneous disorder. At least 33 genes have been linked to this disease to date (Fassone and Rahman 2012).
NDUFV1-associated mitochondrial complex I deficiency is inherited in an autosomal recessive pattern. Defects in the NDUFV1 gene, which encodes for a structural subunit that carries the NADH-binding site of mitochondrial complex I, are frequently identified in cases of mitochondrial complex I deficiency (Koene et al. 2012; Schuelke et al. 1999). Approximately thirty different causative variants have been reported in NDUFV1 (Human Gene Mutation Database; http://www.hgmd.cf.ac.uk/ac/index.php). The majority of these variants are missense changes, although nonsense and splicing variants have also been described, in addition to several deletions.
Full gene sequencing of NDUFV1 is performed, with bidirectional sequencing of exons 1-10. The full coding region of each exon plus ~20 bp of non-coding DNA on either side of the exon are sequenced. We will also sequence any single exon (Test #100) or pair of exons (Test #200) in family members of patients with known mutations or to confirm research results.
Indications for Test
NDUFV1 sequencing should be considered for patients who present with symptoms consistent with mitochondrial complex I (CI) deficiency or for individuals with a family history of mitochondrial CI deficiency.
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- Genetic Counselor Team - email@example.com
- Kym Bliven, PhD - firstname.lastname@example.org
- Fassone E. and Rahman S. 2012. Journal of Medical Genetics. 49:578-90. PubMed ID: 22972949
- Human Gene Mutation Database (Bio-base).
- Koene S. et al. 2012. Journal of Inherited Metabolic Disease. 35:737-47. PubMed ID: 22644603
- Lake N.J. et al. 2015. Journal of Neuropathology & Experimental Neurology. 74:482-92. PubMed ID: 25978847
- Laugel V. et al. 2007. Pediatric Neurology. 36:54-7. PubMed ID: 17162199
- Ortega-Recalde O. et al. 2013. Mitochondrion. 13:749-54. PubMed ID: 23562761
- Rahman S. and Thorburn, D. 2015. Nuclear Gene-Encoded Leigh Syndrome Overview. In: Pagon RA, Adam MP, Bird TD, Dolan CR, Fong C-T, Smith RJ, and Stephens K, editors. GeneReviews(®), Seattle (WA): University of Washington, Seattle. PubMed ID: 26425749
- Sazanov L.A. et al. 2015. Nature Reviews Molecular Cellular Biology. 16:375-88. PubMed ID: 25991374
- Scaglia F. et al. 2004. Pediatrics. 114:925-31. PubMed ID: 15466086
- Schuelke M. et al. 1999. Nature Genetics. 21:260-1. PubMed ID: 10080174
- Skladal D. et al. 2003. Brain. 126:1905-12. PubMed ID: 12805096
Bi-Directional Sanger Sequencing
Nomenclature for sequence variants was from the Human Genome Variation Society (http://www.hgvs.org). As required, DNA is extracted from the patient specimen. PCR is used to amplify the indicated exons plus additional flanking non-coding sequence. After cleaning of the PCR products, cycle sequencing is carried out using the ABI Big Dye Terminator v.3.0 kit. Products are resolved by electrophoresis on an ABI 3730xl capillary sequencer. In most cases, sequencing is performed in both forward and reverse directions; in some cases, sequencing is performed twice in either the forward or reverse directions. In nearly all cases, the full coding region of each exon as well as 20 bases of non-coding DNA flanking the exon are sequenced.
As of March 2016, we compared 17.37 Mb of Sanger DNA sequence generated at PreventionGenetics to NextGen sequence generated in other labs. We detected only 4 errors in our Sanger sequences, and these were all due to allele dropout during PCR. For Proficiency Testing, both external and internal, in the 12 years of our lab operation we have Sanger sequenced roughly 8,800 PCR amplicons. Only one error has been identified, and this was due to sequence analysis error.
Our Sanger sequencing is capable of detecting virtually all nucleotide substitutions within the PCR amplicons. Similarly, we detect essentially all heterozygous or homozygous deletions within the amplicons. Homozygous deletions which overlap one or more PCR primer annealing sites are detectable as PCR failure. Heterozygous deletions which overlap one or more PCR primer annealing sites are usually not detected (see Analytical Limitations). All heterozygous insertions within the amplicons up to about 100 nucleotides in length appear to be detectable. Larger heterozygous insertions may not be detected. All homozygous insertions within the amplicons up to about 300 nucleotides in length appear to be detectable. Larger homozygous insertions may masquerade as homozygous deletions (PCR failure).
In exons where our sequencing did not reveal any variation between the two alleles, we cannot be certain that we were able to PCR amplify both of the patient’s alleles. Occasionally, a patient may carry an allele which does not amplify, due for example to a deletion or a large insertion. In these cases, the report contains no information about the second allele.
Similarly, our sequencing tests have almost no power to detect duplications, triplications, etc. of the gene sequences.
In most cases, only the indicated exons and roughly 20 bp of flanking non-coding sequence on each side are analyzed. Test reports contain little or no information about other portions of the gene, including many regulatory regions.
In nearly all cases, we are unable to determine the phase of sequence variants. In particular, when we find two likely causative mutations for recessive disorders, we cannot be certain that the mutations are on different alleles.
Our ability to detect minor sequence variants, due for example to somatic mosaicism is limited. Sequence variants that are present in less than 50% of the patient’s nucleated cells may not be detected.
Runs of mononucleotide repeats (eg (A)n or (T)n) with n >8 in the reference sequence are generally not analyzed because of strand slippage during PCR and cycle sequencing.
Unless otherwise indicated, the sequence data that we report are based on DNA isolated from a specific tissue (usually leukocytes). Test reports contain no information about gene sequences in other tissues.
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(Delivery accepted Monday - Saturday)
- Send in screw cap tube at least 5 µg -10 µg of purified DNA at a concentration of at least 20 µg/ml for NGS and Sanger tests and at least 5 µg of purified DNA at a concentration of at least 100 µg/ml for gene-centric aCGH, MLPA, and CMA tests, minimum 2 µg for limited specimens.
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