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Charcot Marie Tooth - Demyelinating Neuropathy Sequencing Panel
- Summary and Pricing
- Clinical Features and Genetics
- Citations
- Methods
- Ordering/Specimens
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TEST METHODS
- NextGen Sequencing using PG-Select Capture Probes
- Deletion/Duplication Testing via Array Comparative Genomic Hybridization
NGS Sequencing
| Test Code | Test Copy Genes | CPT Code Copy CPT Codes | |
|---|---|---|---|
| 2643 | COX6A1 | 81479 | Add |
| CTDP1 | 81479 | ||
| DNM2 | 81479 | ||
| EGR2 | 81404 | ||
| FBLN5 | 81479 | ||
| FGD4 | 81479 | ||
| FIG4 | 81406 | ||
| GDAP1 | 81405 | ||
| GJB1 | 81403 | ||
| GNB4 | 81479 | ||
| HK1 | 81479 | ||
| INF2 | 81406 | ||
| KARS | 81479 | ||
| LITAF | 81404 | ||
| MPZ | 81405 | ||
| MTMR2 | 81479 | ||
| NDRG1 | 81479 | ||
| NEFL | 81405 | ||
| PLEKHG5 | 81479 | ||
| PMP22 | 81325 | ||
| PRX | 81405 | ||
| SBF1 | 81479 | ||
| SBF2 | 81479 | ||
| SH3TC2 | 81406 | ||
| YARS | 81479 | ||
| Full Panel Price* | $640.00 | ||
| Test Code | Test Copy Genes | Total Price | CPT Codes Copy CPT Codes | |
|---|---|---|---|---|
| 2643 | Genes x (25) |
$640.00 | 81325, 81403, 81404(x2), 81405(x4), 81406(x3), 81479(x14) | Add |
Pricing Comment
We are happy to accommodate requests for single genes or a subset of these genes. The price will remain the list price. If desired, free reflex testing to remaining genes on panel is available. Alternatively, a single gene or subset of genes can also be ordered on our PGxome Custom Panel.
Targeted Testing
For ordering targeted known variants, please proceed to our Targeted Variants landing page.
Turnaround Time
The great majority of tests are completed within 20 days.
Clinical Sensitivity
A genetic etiology can be identified in approximately 50-70% of individuals with CMT (Saporta et al. 2011; Rossor et al. 2013). Specifically, a molecular diagnosis can be identified in approximately 80-85% of individuals with demyelinating neuropathy (CMT1), and a molecular diagnosis can be identified in approximately 25-35% of individuals with axonal neuropathy (CMT2) (Bird 2015; Bird 2015; Rossor et al. 2013). The sensitivity of this panel will vary based on the clinical phenotype of the patient. It is estimated that ~70% of all Charcot Marie Tooth Type 1 (CMT1) is due to the PMP22 1.5 Mb duplication, while only around 5% of CMT1 cases are due to point mutations (Bird 2015). This NGS sequencing panel will not detect the common 1.5 Mb duplication or deletion in the PMP22 gene.
Deletion/Duplication Testing via aCGH
| Test Code | Test Copy Genes | Individual Gene Price | CPT Code Copy CPT Codes | |
|---|---|---|---|---|
| 600 | COX6A1 | $990.00 | 81479 | Add |
| CTDP1 | $990.00 | 81479 | ||
| DNM2 | $990.00 | 81479 | ||
| EGR2 | $990.00 | 81479 | ||
| FBLN5 | $990.00 | 81479 | ||
| FGD4 | $990.00 | 81479 | ||
| FIG4 | $990.00 | 81479 | ||
| GDAP1 | $990.00 | 81479 | ||
| GJB1 | $990.00 | 81479 | ||
| GNB4 | $990.00 | 81479 | ||
| HK1 | $990.00 | 81479 | ||
| INF2 | $990.00 | 81479 | ||
| KARS | $990.00 | 81479 | ||
| LITAF | $990.00 | 81479 | ||
| MPZ | $990.00 | 81479 | ||
| MTMR2 | $990.00 | 81479 | ||
| NDRG1 | $990.00 | 81479 | ||
| NEFL | $990.00 | 81479 | ||
| PLEKHG5 | $990.00 | 81479 | ||
| PMP22 | $990.00 | 81324 | ||
| PRX | $990.00 | 81479 | ||
| SBF1 | $990.00 | 81479 | ||
| SBF2 | $990.00 | 81479 | ||
| SH3TC2 | $990.00 | 81479 | ||
| YARS | $990.00 | 81479 | ||
| Full Panel Price* | $1490.00 | |||
| Test Code | Test Copy Genes | Total Price | CPT Codes Copy CPT Codes | |
|---|---|---|---|---|
| 600 | Genes x (25) |
$1490.00 | 81324, 81479(x24) | Add |
Pricing Comment
|
# of Genes Ordered |
Total Price |
|
1 |
$990 |
|
2-5 |
$1190 |
|
6-10 |
$1290 |
|
11-100 |
$1490 |
|
Over 100 |
Call for quote |
Turnaround Time
The great majority of tests are completed within 20 days.
Clinical Sensitivity
Large deletions/duplications have been reported in the FIG4 gene, but no large-scale study has been done (Human Gene Mutation Database).
Clinical Features
Charcot Marie Tooth disease (CMT), also known as hereditary motor and sensory neuropathy (HMSN) is a large group of inherited disorders of the peripheral nerves. The progressive degeneration of motor nerves results in weakness and atrophy of the distal muscles. The degeneration of sensory nerves leads to decreased sensation, tingling and numbness in the legs, feet, arms and hands and neuropathic pain. The age of onset varies from childhood to mid adulthood. Symptoms usually begin with weakness and atrophy in the muscles of the legs and feet. As the disease progresses, weakness and atrophy of the muscles of the arms and hands may occur. CMT is heterogeneous in regards to symptoms, severity and progression rate. Although the disease may lead to disability and respiratory difficulty, life expectancy is usually unaffected. Most common symptoms include foot deformity, loss of balance, hammertoes, foot drop, frequent tripping and falls, and reduced manual dexterity (Bird 2015). Diagnosis is based on clinical features, family history, neurological examination, and electromyography (EMG) and nerve conduction velocity (NCV) findings (Rossor et al. 2013; Bird 2015). CMT affects approximately 1 in 3,300 people (Bird 2015; Saporta et al. 2011). Demyelinating forms of CMT primarily affect the myelin sheath of the peripheral nerve and are characterized by slow nerve conduction velocities (NCV) of less than 38 m/s in upper limbs. Axonal forms of CMT primarily affect the axons of the peripheral nerves and are characterized by normal or almost normal NCV of greater than 38 m/s. Intermediate NCV of 25-45 m/s can be difficult to classify as axonal or demyelinating. This panel includes genes that cause a strict CMT1 (demyelinating) phenotype, in addition to genes that cause intermediate forms with axonal and/or demyelinating conductions. Approximately 70% of CMT1 is caused by the recurrent PMP22 duplication (Bird 2015; Li et al. 2013; van Paassen et al. 2014). CMT1A is most commonly caused by a 1.5 Mb duplication of chromosome 17p11.2 which includes the PMP22 gene. PMP22 deletion/duplication testing via aCGH can be ordered through test code #600.
Genetics
Demyelinating neuropathies can be inherited in an autosomal dominant, autosomal recessive or an X-linked manner. The MPZ, LITAF, NEFL, PMP22, FBLN5, YARS, INF2, GNB4 genes are involved in autosomal dominant CMT. Autosomal recessive forms of CMT involve the MTMR2, SBF2, SBF1, SH3TC2, PRX, FGD4, FIG4, NDRG1, HK1, KARS, CTDP1, PLEKHG5, and COX6A1 genes. Pathogenic variants in the EGR2, GDAP1, and DNM2 genes can exhibit both dominant and recessive inheritance. Pathogenic variants in the GJB1 gene are inherited in an X-linked dominant manner. See individual gene test descriptions for information on molecular biology of gene products. The most common genetic cause of CMT1 is a 1.5 Mb duplication of chromosome 17p11.2 which includes the PMP22 gene. This sequencing test will not detect this large copy number variant.
Testing Strategy
For this NGS panel, the full coding regions plus ~10 bp of non-coding DNA flanking each exon are sequenced for each of the genes listed below. Sequencing is accomplished by capturing specific regions with an optimized solution-based hybridization method, followed by massively parallel sequencing of the captured DNA fragments. Additional Sanger sequencing is performed for any regions not captured or with insufficient number of sequence reads. All pathogenic, undocumented and questionable variant calls are confirmed by Sanger sequencing. Please note that exon 8 of the INF2 gene is not currently included this panel. Thus far, only exons 2 to 6, especially exons 2 to 4 that encode the diaphanous inhibitory domain (DID), have been reported to harbor pathogenic INF2 variants (Boyer et al. 2011; Barua et al. 2013; Human Gene Mutation Database).
Indications for Test
Individuals with clinical symptoms consistent with a demyelinating neuropathy (nerve conduction velocities of less than 38 m/s).
Genes
| Official Gene Symbol | OMIM ID |
|---|---|
| COX6A1 | 602072 |
| CTDP1 | 604927 |
| DNM2 | 602378 |
| EGR2 | 129010 |
| FBLN5 | 604580 |
| FGD4 | 611104 |
| FIG4 | 609390 |
| GDAP1 | 606598 |
| GJB1 | 304040 |
| GNB4 | 610863 |
| HK1 | 142600 |
| INF2 | 610982 |
| KARS | 601421 |
| LITAF | 603795 |
| MPZ | 159440 |
| MTMR2 | 603557 |
| NDRG1 | 605262 |
| NEFL | 162280 |
| PLEKHG5 | 611101 |
| PMP22 | 601097 |
| PRX | 605725 |
| SBF1 | 603560 |
| SBF2 | 607697 |
| SH3TC2 | 608206 |
| YARS | 603623 |
| Inheritance | Abbreviation |
|---|---|
| Autosomal Dominant | AD |
| Autosomal Recessive | AR |
| X-Linked | XL |
| Mitochondrial | MT |
Diseases
Related Tests
CONTACTS
Genetic Counselors
- Genetic Counselor Team - clinicaldnatesting@preventiongenetics.com
Geneticist
- Angela Gruber, PhD - angela.gruber@preventiongenetics.com
Citations
- Barua M. et al. 2013. Kidney International. 83: 316-22. PubMed ID: 23014460
- Bird T.D. 2015. Charcot-Marie-Tooth Hereditary Neuropathy 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: 20301532
- Bird T.D. 2015. Charcot-Marie-Tooth Neuropathy Type 1. 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: 20301384
- Boyer O. et al. 2011. Journal of the American Society of Nephrology : Jasn. 22: 239-45. PubMed ID: 21258034
- Human Gene Mutation Database (Bio-base).
- Li J. et al. 2013. Molecular Neurobiology. 47: 673-98. PubMed ID: 23224996
- Rossor Alexander M. et al. 2013. Nature Reviews Neurology. 9: 562-571. PubMed ID: 24018473
- Saporta A.S. et al. 2011. Annals of Neurology. 69: 22-33. PubMed ID: 21280073
- van Paassen B.W. et al. 2014. Orphanet Journal of Rare Diseases. 9: 38. PubMed ID: 24646194
Order Kits
TEST METHODS
- NextGen Sequencing using PG-Select Capture Probes
- Deletion/Duplication Testing via Array Comparative Genomic Hybridization
NextGen Sequencing using PG-Select Capture Probes
Test Procedure
We use a combination of Next Generation Sequencing (NGS) and Sanger sequencing technologies to cover the full coding regions of the listed genes plus ~20 bases of non-coding DNA flanking each exon. As required, genomic DNA is extracted from the patient specimen. For NGS, patient DNA corresponding to these regions is captured using an optimized set of DNA hybridization probes. Captured DNA is sequenced using Illumina’s Reversible Dye Terminator (RDT) platform (Illumina, San Diego, CA, USA). Regions with insufficient coverage by NGS are covered by Sanger sequencing. All pathogenic, likely pathogenic, or variants of uncertain significance are confirmed by Sanger sequencing.
For Sanger sequencing, Polymerase Chain Reaction (PCR) is used to amplify targeted regions. After purification of the PCR products, cycle sequencing is carried out using the ABI Big Dye Terminator v.3.0 kit. PCR products are resolved by electrophoresis on an ABI 3730xl capillary sequencer. In nearly all cases, cycle sequencing is performed separately in both the forward and reverse directions.
Patient DNA sequence is aligned to the genomic reference sequence for the indicated gene region(s). All differences from the reference sequences (sequence variants) are assigned to one of five interpretation categories, listed below, per ACMG Guidelines (Richards et al. 2015).
(1) Pathogenic Variants
(2) Likely Pathogenic Variants
(3) Variants of Uncertain Significance
(4) Likely Benign Variants
(5) Benign, Common Variants
Human Genome Variation Society (HGVS) recommendations are used to describe sequence variants (http://www.hgvs.org). Rare variants and undocumented variants are nearly always classified as likely benign if there is no indication that they alter protein sequence or disrupt splicing.
Analytical Validity
As of March 2016, 6.36 Mb of sequence (83 genes, 1557 exons) generated in our lab was compared between Sanger and NextGen methodologies. We detected no differences between the two methods. The comparison involved 6400 total sequence variants (differences from the reference sequences). Of these, 6144 were nucleotide substitutions and 256 were insertions or deletions. About 65% of the variants were heterozygous and 35% homozygous. The insertions and deletions ranged in length from 1 to over 100 nucleotides.
In silico validation of insertions and deletions in 20 replicates of 5 genes was also performed. The validation included insertions and deletions of lengths between 1 and 100 nucleotides. Insertions tested in silico: 2200 between 1 and 5 nucleotides, 625 between 6 and 10 nucleotides, 29 between 11 and 20 nucleotides, 25 between 21 and 49 nucleotides, and 23 at or greater than 50 nucleotides, with the largest at 98 nucleotides. All insertions were detected. Deletions tested in silico: 1813 between 1 and 5 nucleotides, 97 between 6 and 10 nucleotides, 32 between 11 and 20 nucleotides, 20 between 21 and 49 nucleotides, and 39 at or greater than 50 nucleotides, with the largest at 96 nucleotides. All deletions less than 50 nucleotides in length were detected, 13 greater than 50 nucleotides in length were missed. Our standard NextGen sequence variant calling algorithms are generally not capable of detecting insertions (duplications) or heterozygous deletions greater than 100 nucleotides. Large homozygous deletions appear to be detectable.
Analytical Limitations
Interpretation of the test results is limited by the information that is currently available. Better interpretation should be possible in the future as more data and knowledge about human genetics and this specific disorder are accumulated.
When Sanger sequencing does not reveal any difference from the reference sequence, or when a sequence variant is homozygous, we cannot be certain that we were able to detect both patient alleles. Occasionally, a patient may carry an allele which does not amplify, due to a large deletion or insertion. In these cases, the report will contain no information about the second allele. Our Sanger and NGS Sequencing tests are generally not capable of detecting Copy Number Variants (CNVs).
We sequence all coding exons for each given transcript, plus ~20 bp of flanking non-coding DNA for each exon. Test reports contain no information about other portions of the gene, such as regulatory domains, deep intronic regions or any currently uncharacterized alternative exons.
In most 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 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.
Unless otherwise indicated, DNA sequence data is obtained from a specific cell-type (usually leukocytes from whole blood). Test reports contain no information about the DNA sequence in other cell-types.
We cannot be certain that the reference sequences are correct.
Rare, low probability interpretations of sequencing results, such as for example the occurrence of de novo mutations in recessive disorders, are generally not included in the reports.
We have confidence in our ability to track a specimen once it has been received by PreventionGenetics. However, we take no responsibility for any specimen labeling errors that occur before the sample arrives at PreventionGenetics.
Deletion/Duplication Testing via Array Comparative Genomic Hybridization
Test Procedure
Equal amounts of genomic DNA from the patient and a gender matched reference sample are amplified and labeled with Cy3 and Cy5 dyes, respectively. To prevent any sample cross contamination, a unique sample tracking control is added into each patient sample. Each labeled patient product is then purified, quantified, and combined with the same amount of reference product. The combined sample is loaded onto the designed array and hybridized for at least 22-42 hours at 65°C. Arrays are then washed and scanned immediately with 2.5 µM resolution. Only data for the gene(s) of interest for each patient are extracted and analyzed.
Analytical Validity
PreventionGenetics' high density gene-centric custom designed aCGH enables the detection of relatively small deletions and duplications within a single exon of a given gene or deletions and duplications encompassing the entire gene. PreventionGenetics has established and verified this test's accuracy and precision.
Analytical Limitations
Our dense probe coverage may allow detection of deletions/duplications down to 100 bp; however due to limitations and probe spacing this cannot be guaranteed across all exons of all genes. Therefore, some copy number changes smaller than 100-300 bp within a targeted large exon may not be detected by our array.
This array may not detect deletions and duplications present at low levels of mosaicism or those present in genes that have pseudogene copies or repeats elsewhere in the genome.
aCGH will not detect balanced translocations, inversions, or point mutations that may be responsible for the clinical phenotype.
Breakpoints, if occurring outside the targeted gene, may be hard to define.
The sensitivity of this assay may be reduced when DNA is extracted by an outside laboratory.
Order Kits
Ordering Options
myPrevent - Online Ordering
- The test can be added to your online orders in the Summary and Pricing section.
- Once the test has been added log in to myPrevent to fill out an online requisition form.
REQUISITION FORM
- A completed requisition form must accompany all specimens.
- Billing information along with specimen and shipping instructions are within the requisition form.
- All testing must be ordered by a qualified healthcare provider.
SPECIMEN TYPES
WHOLE BLOOD
(Delivery accepted Monday - Saturday)
- Collect 3 ml -5 ml (5 ml preferred) of whole blood in EDTA (purple top tube) or ACD (yellow top tube). For Test #500-DNA Banking only, collect 10 ml -20 ml of whole blood.
- For small babies, we require a minimum of 1 ml of blood.
- Only one blood tube is required for multiple tests.
- Ship blood tubes at room temperature in an insulated container. Do not freeze blood.
- During hot weather, include a frozen ice pack in the shipping container. Place a paper towel or other thin material between the ice pack and the blood tube.
- In cold weather, include an unfrozen ice pack in the shipping container as insulation.
- At room temperature, blood specimen is stable for up to 48 hours.
- If refrigerated, blood specimen is stable for up to one week.
- Label the tube with the patient name, date of birth and/or ID number.
DNA
(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.
- For requests requiring more than one test, send an additional 5 µg DNA per test ordered when possible.
- DNA may be shipped at room temperature.
- Label the tube with the composition of the solute, DNA concentration as well as the patient’s name, date of birth, and/or ID number.
- We only accept genomic DNA for testing. We do NOT accept products of whole genome amplification reactions or other amplification reactions.
CELL CULTURE
(Delivery preferred Monday - Thursday)
- PreventionGenetics should be notified in advance of arrival of a cell culture.
- Culture and send at least two T25 flasks of confluent cells.
- Some panels may require additional flasks (dependent on size of genes, amount of Sanger sequencing required, etc.). Multiple test requests may also require additional flasks. Please contact us for details.
- Send specimens in insulated, shatterproof container overnight.
- Cell cultures may be shipped at room temperature or refrigerated.
- Label the flasks with the patient name, date of birth, and/or ID number.
- We strongly recommend maintaining a local back-up culture. We do not culture cells.
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