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Melanoma Predisposition via CDKN2A Gene Sequencing with CNV Detection

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

Sequencing and CNV

Test Code Test Copy GenesPriceCPT Code Copy CPT Codes
7397 CDKN2A$540 81404,81479 Add to Order

New York State Approved Test

Pricing Comments

This test is also offered via our exome backbone with CNV detection (click here). The exome-based test may be higher priced, but permits reflex to the entire exome or to any other set of clinically relevant genes.

Targeted Testing

For ordering sequencing of 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

It has been reported that 25% to 50% of familial melanoma kindreds are affected by a CDKN2A causative mutation (Goldstein et al. J Med Genet 44(2):99-106, 2007). Individuals with multiple primary melanomas have a 1-3% chance of having a CDKN2A causative mutation (Berwick et al. Cancer Epidemiol Biomarkers Prev 15:1520-5, 2006).

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Clinical Features

Melanoma is a malignant tumor that originated in melanocytes, a specialized cell type that produces melanin pigments that determine skin, hair and eye color (Lin and Fisher. Nature 445:843–850, 2007). Over the past few decades there has been a rise in the incidence of melanoma due both to improved awareness leading to additional diagnoses and to lifestyle changes that have resulted in an increase in sun exposure (Mehnert and Kluger. Curr Oncol Rep 14:449–457, 2012). Most melanomas occur as sporadic cases with no recognized familial component; however melanoma has been reported to be twice as common in persons with an affected parent, three times as common if a sibling is affected, and nine times as common if both a parent and a sibling are affected (Hemminki et al. J Invest Dermatol 120:217–223, 2003). Familial clustering is likely the result of genetic and environmental factors. Heritable alleles for melanoma susceptibility range from high-risk, high-penetrance alleles that are rare, to low-risk, low-penetrance alleles that are common (Nelson et al. Clinics in Dermatology 27, 46–52, 2009). Mutations in the highly penetrant gene CDKN2A, and less frequently the CDK4 gene, are responsible for the majority of predisposition to melanoma cases. Individuals with genetic predisposition to melanoma have an earlier age of onset. For example, the median age at melanoma diagnosis is significantly lower in carriers of CDKN2A mutations (36 years) than in patients from families with wildtype CDKN2A (45 years) (Goldstein et al. Cancer Res 66:9818–9828, 2006). A family history of melanoma and pancreatic cancer may also suggest inherited mutations in CDKN2A (Goldstein et al. J Natl Cancer Inst 92(12):1006-10, 2000).

Genetics

Melanoma predisposition is inherited in an autosomal dominant manner. The strongest genetic risk for the development of melanoma results from heritable alterations in the cyclin-dependent kinase inhibitor 2A (CDKN2A) gene, which encodes two separate but related proteins, p16/INK4a and p14/ARF, by using two different promoters. The CDKN2A gene is a tumor suppressor, and its protein products help regulate cell division and apoptosis (Nelson et al., 2009). The p16/INK4a protein is produced from a transcript generated from exons 1α, 2 and 3, whereas p14ARF is produced, using an alternative reading frame, from a transcript comprising exons 1β, 2 and 3 (Lin and Fisher, 2007). The function of the p16/INK4a protein is to inhibit CDK4/6 protein-mediated phosphorylation of the Rb (Retinoblastoma) tumor suppressor protein; dephosphorylated Rb is the active state. Mutated p16/INK4a leads to phosphorylation of Rb, which in turn results in release of the bound transcription factor E2F, which then allows the cell to undergo unregulated cell division leading to the development of melanoma. p14/ARF exerts its regulation of cell division through its indirect interaction with the p53 protein. p14/ARF binds to and inhibits the HDM2 protein. HDM2 functions to ubiquitinate proteins and target them for degradation, Mutations in p14/ARF abrogate binding to HDM2. As a result, HDM2 is released and increases ubiquitination of p53 leading to increased destruction of this tumor suppressor. The main functions of p53 are to sense genetic damage to allow pause for DNA repair and to activate cellular apoptosis. Thus, the decreased levels of p53 associated with mutations in p14/ARF lead to genetic instability and to a higher risk of melanoma in individuals with CDKN2A mutations (Lin and Fisher, 2007). Families with mutated p14/ARF proteins also have an increase in neural system tumors in addition to melanoma (Nelson et al., 2009). CDKN2A causative mutations reported to date include mostly missense mutations, however nonsense, splicing, small insertions and deletions, regulatory, and gross insertions and deletions have also been reported (Human Gene Mutation Database).

Testing Strategy

For this Next Generation Sequencing (NGS) test, 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 regions not captured or with insufficient number of sequence reads.

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.

Copy number variants (CNVs) are also detected from NGS data. We utilize a CNV calling algorithm that compares mean read depth and distribution for each target in the test sample against multiple matched controls. Neighboring target read depth and distribution and zygosity of any variants within each target region are used to reinforce CNV calls. All CNVs are confirmed using another technology such as aCGH, MLPA, or PCR before they are reported.

This test provides full coverage of all coding exons of the CDKN2A gene, plus ~10 bases of flanking noncoding DNA. We define full coverage as >20X NGS reads or Sanger sequencing.

Indications for Test

Candidates for this test are Individuals who have multiple family members with melanoma. Some members of the melanoma families may have other forms of cancer, particularly pancreatic cancer (Goldstein et al., 2000). In such families, it is best to test an affected individual first. Other candidates are patients with multiple primary melanomas. This test is specifically designed for heritable germline mutations and is not appropriate for the detection of somatic mutations in tumor tissue.

Gene

Official Gene Symbol OMIM ID
CDKN2A 600160
Inheritance Abbreviation
Autosomal Dominant AD
Autosomal Recessive AR
X-Linked XL
Mitochondrial MT

CONTACTS

Genetic Counselors
Geneticist
Citations
  • Berwick M. 2006. The Prevalence of CDKN2A Germ-Line Mutations and Relative Risk for Cutaneous Malignant Melanoma: An International Population-Based Study. Cancer Epidemiology Biomarkers & Prevention 15: 1520–1525. PubMed ID: 16896043
  • Goldstein AM, Chan M, Harland M, Hayward NK, Demenais F, Timothy Bishop D, Azizi E, Bergman W, Bianchi-Scarra G, Bruno W, Calista D, Cannon Albright LA, et al. 2006. Features associated with germline CDKN2A mutations: a GenoMEL study of melanoma-prone families from three continents. Journal of Medical Genetics 44: 99–106. PubMed ID: 16905682
  • Goldstein et al. (2000) "Genotype-phenotype relationships in U.S. melanoma-prone families with CDKN2A and CDK4 mutations." J Natl Cancer Inst 92(12):1006-10. PubMed ID: 10861313
  • Goldstein et al. (2006). "High-risk melanoma susceptibility genes and pancreatic cancer, neural system tumors, and uveal melanoma across GenoMEL." Cancer Res 66:9818–9828. PubMed ID: 17047042
  • Hemminki et al. (2003). "Familial and attributable risks in cutaneous melanoma: effects of proband and age." J Invest Dermatol 120:217–223. PubMed ID: 12542525
  • Human Gene Mutation Database (Bio-base).
  • Lin JY, Fisher DE. 2007. Melanocyte biology and skin pigmentation. Nature 445: 843–850. PubMed ID: 17314970
  • Mehnert and Kluger. (2012). "Driver mutations in melanoma: lessons learned from bench-to-bedside studies." Curr Oncol Rep 14:449–457. PubMed ID: 22723080
  • Nelson AA, Tsao H. 2009. Melanoma and genetics. Clinics in Dermatology 27: 46–52. PubMed ID: 19095153
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TEST METHODS

Sequencing and CNV Detection via NextGen Sequencing using PG-Select Capture Probes

Test Procedure

NextGen Sequencing

We use a combination of Next Generation Sequencing (NGS) and Sanger sequencing technologies to cover the full coding regions of the listed genes plus ~10 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.

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 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.

Deletion and Duplication Testing via NGS

Copy number variants (CNVs) such as deletions and duplications are detected from next generation sequencing data. We utilize a CNV calling algorithm that compares mean read depth and distribution for each target in the test sample against multiple matched controls. Neighboring target read depth and distribution, and zygosity of any variants within each target region are used to reinforce CNV calls. All CNVs are confirmed using another technology such as PCR, aCGH or MLPA before they are reported.
Analytical Validity

NextGen Sequencing

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.

Deletion and Duplication Testing via NGS
 
In general, sensitivity for single, double, or triple exon CNVs is ~80% and for CNVs of four exon size or larger is close to 100%, but may vary from gene-to-gene based on exon size, depth of coverage, and characteristics of the region.
Analytical Limitations

NextGen Sequencing

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 ~10 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 and Duplication Testing via NGS
 
This CNV calling algorithm used in this test detects most deletions and duplications; however aberrations in a small percentage of regions may not be accurately detected due to sequence paralogy (e.g. pseudogenes, segmental duplications), sequence properties, deletion/duplication size (e.g. single vs. two or more exons), and inadequate coverage. 
 
Balanced translocations or inversions within a targeted gene, or large unbalanced translocations or inversions that extend beyond the genomic location of a targeted gene are not detected.
 
In nearly all cases, our ability to determine the exact copy number change within a targeted gene is limited. In particular, when we find copy excess within a targeted gene, we cannot be certain that the region is duplicated, triplicated etc. In many duplication cases, we are unable to determine the genomic location or the orientation of the duplicated segment with respect to the gene. In particular, we often cannot determine if the duplicated segment is inserted in tandem within the gene or inserted elsewhere in the genome. Similarly, we may not be able to determine the orientation of the duplicated segment (direct or inverted), and whether it will disrupt the open reading frame of the given gene.
 
Our ability to detect CNVs due to somatic mosaicism is limited.
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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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