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Familial Focal Epilepsy with Variable Foci via the DEPDC5 Gene

  • Summary and Pricing
  • Clinical Features and Genetics
  • Citations
  • Methods
  • Ordering/Specimens
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TEST METHODS

NGS Sequencing

Test Code Test Copy GenesIndividual Gene PriceCPT Code Copy CPT Codes
4387 DEPDC5$990.00 81479 Add to Order
Pricing Comment

Our most cost-effective testing approach is NextGen sequencing with Sanger sequencing supplemented as needed to ensure sufficient coverage and to confirm NextGen calls that are pathogenic, likely pathogenic or of uncertain significance. If, however, full gene Sanger sequencing only is desired (for purposes of insurance billing or STAT turnaround time for example), please see link below for Test Code, pricing, and turnaround time information.

For Sanger Sequencing click here.
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 28 days.

Clinical Sensitivity

DEPDC5 mutations have been reported in 12-37% of families with autosomal dominant focal epilepsy (Dibbens et al. 2013; Ishida et al. 2013). DEPDC5 variants were found in 13% (4/30) of cases of ADNFLE in which no mutations in CHRNA4, CHRNA2, or CHRNB2 were found (Picard et al. 2014).

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Clinical Features

Familial focal epilepsy with variable foci (FFEVF) is a phenotypically heterogeneous form of epilepsy characterized by focal seizures. Seizures can originate from different cortical regions of the brain in members of the same family. Common EEG findings include centro-temporal spikes and temporo-posterior sharp waves. Age of onset ranges from infancy to adulthood (Lal et al. 2014; Ishida et al. 2013). MRI in a subset of FFEVF patients reveals focal cortical dysplasia with thickening of the cortex and blurring of the grey-white junction (Scheffer et al. 2014). MRI findings within a family can be variable, with some members showing no signs of lesional epilepsy. Intellect is generally preserved, although FFEVF patients have been reported with intellectual disability, autism spectrum, or other psychiatric disorders (Dibbens et al. 2013; Scheffer et al. 2014).

Autosomal dominant nocturnal frontal lobe epilepsy (ADNFLE) is a partial seizure disorder characterized by seizures that occur during non-REM sleep. Age of onset is usually between 8 and 12 years of age and patients experience predominantly nocturnal seizures with hyperkinetic, tonic, or dystonic features. ADNFLE can be caused by variants in a number of genes and is usually highly treatable, but 78% of ADNFLE cases caused by DEPDC5 variants are drug resistant (Picard et al. 2014).

Genetics

FFEVF and ADNFLE are inherited in an autosomal dominant manner and can be caused by mutations in the DEPDC5 gene. Nonsense, frameshift, and missense variants have been reported in DEPDC5. De novo mutations in DEPDC5 have been reported, suggesting a role for DEPDC5 in sporadic as well as familial epilepsy cases (Dibbens et al. 2013). The penetrance of DEPDC5 mutations is estimated at 66% (Dibbens et al. 2013; Ishida et al. 2013).

DEPDC5 encodes a highly conserved protein that is expressed in neurons. The DEPDC5 protein is part of the GATOR1 complex that negatively regulates the mTOR pathway (Scheffer et al. 2014). The majority of reported DEPDC5 variants are nonsense mutations that are predicted to result in loss of DEPDC5 function.  It is hypothesized the DEPDC5 mutations lead to increased mTOR signaling and that this underlies the epilepsy phenotype.

Testing Strategy

For this NextGen test, the full coding regions plus ~20 bp of non-coding DNA flanking each exon are sequenced for the gene listed below. Sequencing is accomplished by capturing specific regions with an optimized solution-based hybridization kit, 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, likely pathogenic, or variants of uncertain significance are confirmed by Sanger sequencing.

Indications for Test

Candidates for DEPDC5 sequencing include patients with symptoms of FFEVF who have a family history of focal epilepsy consistent with autosomal dominant inheritance. In addition, DEPDC5 testing should be considered in patients with drug resistant ADNFLE (Picard et al. 2014).

Gene

Official Gene Symbol OMIM ID
DEPDC5 614191
Inheritance Abbreviation
Autosomal Dominant AD
Autosomal Recessive AR
X-Linked XL
Mitochondrial MT

Disease

Name Inheritance OMIM ID
Epilepsy, familial focal, with variable foci 604364

CONTACTS

Genetic Counselors
Geneticist
Citations
  • Dibbens LM, Vries B de, Donatello S, Heron SE, Hodgson BL, Chintawar S, Crompton DE, Hughes JN, Bellows ST, Klein KM, Callenbach PMC, Corbett MA, et al. 2013. Mutations in DEPDC5 cause familial focal epilepsy with variable foci. Nature Genetics 45: 546–551. PubMed ID: 23542697
  • Ishida S, Picard F, Rudolf G, Noé E, Achaz G, Thomas P, Genton P, Mundwiller E, Wolff M, Marescaux C, Miles R, Baulac M, et al. 2013. Mutations of DEPDC5 cause autosomal dominant focal epilepsies. Nature Genetics 45: 552–555. PubMed ID: 23542701
  • Lal D, Reinthaler EM, Schubert J, Muhle H, Riesch E, Kluger G, Jabbari K, Kawalia A, Bäumel C, Holthausen H, Hahn A, Feucht M, et al. 2014. DEPDC5 mutations in genetic focal epilepsies of childhood. Annals of Neurology n/a–n/a. PubMed ID: 24591017
  • Picard F, Makrythanasis P, Navarro V, Ishida S, Bellescize J de, Ville D, Weckhuysen S, Fosselle E, Suls A, Jonghe P De, Vasselon Raina M, Lesca G, et al. 2014. DEPDC5 mutations in families presenting as autosomal dominant nocturnal frontal lobe epilepsy. Neurology. PubMed ID: 24814846
  • Scheffer IE, Heron SE, Regan BM, Mandelstam S, Crompton DE, Hodgson BL, Licchetta L, Provini F, Bisulli F, Vadlamudi L, Gecz J, Connelly A, et al. 2014. Mutations in mTOR regulator DEPDC5 cause focal epilepsy with brain malformations: DEPDC5 focal epilepsy with malformations. Annals of Neurology n/a–n/a. PubMed ID: 24585383
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TEST METHODS

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.

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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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