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Cone-Rod Dystrophy and Retinitis Pigmentosa via the C8orf37 Gene

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

Sequencing

Test Code TestIndividual Gene PriceCPT Code Copy CPT Codes
2237 C8orf37$680.00 81479 Add to Order
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 18 days.

Clinical Sensitivity

Predicting clinical sensitivity for the C8orf37 gene is challenging due to genetic heterogeneity of both cone rod dystrophy and retinitis pigmentosa and also due to the limited number of documented cases. However, analytical sensitivity is expected to be high because all mutations reported are detectable by this method (Human Gene Mutation Database).

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Deletion/Duplication Testing via aCGH

Test Code TestIndividual Gene PriceCPT Code Copy CPT Codes
600 C8orf37$690.00 81479 Add to Order
Pricing Comment

# of Genes Ordered

Total Price

1

$690

2

$730

3

$770

4-10

$840

11-30

$1,290

31-100

$1,670

Over 100

Call for quote

Turnaround Time

The great majority of tests are completed within 28 days.

Clinical Features

Cone rod dystrophies (CORDs/CRDs) are characterized by dysfunction or degeneration of cone photoreceptors with relative preservation of rod function in the initial stages. The most common symptoms are photophobia and epiphora in bright light, decreased visual acuity, and dyschromatopsia. Fundus changes may vary from mild pigment granularity to a distinct atrophic lesion in the central macula. As the disease progresses, degeneration of rod photoreceptors also occurs and leads to progressive night blindness and peripheral visual field loss. Cone rod dystrophies (1/40,000) are 10 times less common than RP (Hamel. 2007). Retinitis pigmentosa (RP) represents a group of hereditary retinal dystrophies with a worldwide prevalence of ~1 in 4000 (Booij et al. 2005). RP is clinically characterized by retinal pigment deposits visible on fundus examination, nyctalopia ("night blindness"), followed by progressive degeneration of the photoreceptors, which eventually leads to blindness (van Soest et al. 1999).

Genetics

Genes that are associated with both autosomal recessive (ar) CRD and RP encode proteins that are involved in phototransduction, retinoid metabolism, transport through connecting cilium, cell-to-cell signaling or synaptic interaction (Estrada-Cuzcano et al. 2012). Mutations in C8orf37 can lead to an early or adolescent-onset arCRD or arRP phenotype with early macular atrophy. Postaxial polydactyly has been reported in one family, which suggests a syndromic phenotype (van Huet et al. 2013). C8orf37 encoded polypeptide function is unknown because it lacks known functional protein domains. C8orf37 is expressed ubiquitously. High mRNA expression levels were found in brain, heart, and retina. Immunohistochemical studies revealed that C8orf37 localization at the base of the photoreceptor connecting cilia (Estrada-Cuzcano et al. 2012). Immunolocalization study, and the presence of postaxial polydactyly in one of the families who had C8orf37 mutations suggested a plausible ciliary function of the C8orf37 encoded polypeptide (Estrada-Cuzcano et al. 2012; van Huet et al. 2013). These studies also suggest that C8ORF37 may be implicated in Bardet-Biedl syndrome or in other ciliopathies. Only a few causative mutations have been reported in C8orf37. These are missense, nonsense and splicing (Human Gene Mutation Database). C8orf37 mutation analysis in 4 unrelated consanguineous families with retinal dystrophies identified homozygous C8orf37 mutations in all affected individuals (Estrada-Cuzcano et al. 2012).

Testing Strategy

This test involves bidirectional Sanger sequencing using genomic DNA of all coding exons of the C8orf37 gene plus ~20 bp of flanking non-coding DNA on each side. We will also sequence any single exon (Test #100) or pair of exons (Test #200) in family members of patients with known pathogenic variants or to confirm research results.

Indications for Test

All patients with symptoms suggestive of Cone-rod dystrophy.

Gene

Official Gene Symbol OMIM ID
C8orf37 614477
Inheritance Abbreviation
Autosomal Dominant AD
Autosomal Recessive AR
X-Linked XL
Mitochondrial MT

Disease

Name Inheritance OMIM ID
Cone-rod dystrophy 16 AR 614500

Related Tests

Name
Autism Spectrum Disorders and Intellectual Disability (ASD-ID) Comprehensive Panel
Autosomal Recessive Retinitis Pigmentosa Sequencing Panel
Comprehensive Inherited Retinal Dystrophies (includes RPGR ORF15) Sequencing Panel
Cone-Rod Dystrophy Sequencing Panel
Retinitis Pigmentosa (includes RPGR ORF15) Sequencing Panel

CONTACTS

Genetic Counselors
Geneticist
Citations
  • Booij JC. et al. 2005. Journal of medical genetics. 42: e67. PubMed ID: 16272259
  • Estrada-Cuzcano A, Neveling K, Kohl S, Banin E, Rotenstreich Y, Sharon D, Falik-Zaccai TC, Hipp S, Roepman R, Wissinger B, Letteboer SJF, Mans DA, et al. 2012. Mutations in C8orf37, Encoding a Ciliary Protein, are Associated with Autosomal-Recessive Retinal Dystrophies with Early Macular Involvement. The American Journal of Human Genetics 90: 102–109. PubMed ID: 22177090
  • Hamel CP. 2007. Cone rod dystrophies. Orphanet J Rare Dis 1;2:7. PubMed ID: 17270046
  • Human Gene Mutation Database (Bio-base).
  • van Huet RA, Estrada-Cuzcano A, Banin E, Rotenstreich Y, Hipp S, Kohl S, Hoyng CB, Hollander AI den, Collin RW, Klevering BJ. 2013. Clinical characteristics of rod and cone photoreceptor dystrophies in patients with mutations in the C8orf37 gene. Investigative ophthalmology & visual science 54: 4683–4690. PubMed ID: 23788369
  • Van Soest S., Westerveld A. 1999. Survey of ophthalmology. 43: 321-34. PubMed ID: 10025514
Order Kits
TEST METHODS

Bi-Directional Sanger Sequencing

Test Procedure

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.

Analytical Validity

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).

Analytical Limitations

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.

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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