Forms

Retinitis Pigmentosa via the CNGB1 Gene

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

Sequencing

Test Code Test Copy GenesIndividual Gene PriceCPT Code Copy CPT Codes
687 CNGB1$1340.00 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
Unknown.

See More

See Less

Clinical Features

Nonsyndromic Retinitis Pigmentosa (RP, OMIM # 268000) is a large group of inherited degenerative diseases of the retina characterized by abnormalities of the photoreceptors or the retinal pigment epithelium. It is a progressive disease. Symptoms usually begin with night blindness, progressing to constriction of the peripheral visual field and, eventually, to loss of central vision. The age of onset varies from childhood to middle age (Gu et al. J Med Genet 36:705-707, 1999). The clinical hallmarks are abnormal fundus with bone-spicule deposits and attenuated retinal vessels, abnormal electroretinographic findings and reduced visual fields (Daiger et al. Arch Ophthalmol 125:151-158, 2007). RP affects 1 in 3,000 people worldwide (Farrar et al. EMBO J 21:857-864, 2002). Genetic abnormalities are the primary cause of RP, which affects all ethnic groups.

Genetics

Retinitis Pigmentosa (RP) is genetically and clinically heterogeneous (Koenekoop et al. Clin Experiment Ophthalmol 35:473-485, 2007). At least 5 distinct subgroups are recognized on the basis of the mode of inheritance and age of onset: autosomal dominant (AD-RP), autosomal recessive (AR-RP), X-linked, digenic (Kajiwara et al. Science 264:1604-1608, 1994), and mitochondrial (Mansergh et al. Am J Hum Genet 64:971-985, 1999). Genetic heterogeneity is documented within each subgroup. Currently, 23 genes are known to cause AR-RP. These include the CNGB1 gene. In a consanguineous family of French origin affected with severe AR-RP, Bareil et al. identified a missense mutation in the CNGB1 gene resulting in the amino acid change Gly993Val (Hum Genet 108:328-334, 2001). Subsequently, Kondo et al. reported a homozygous donor splice mutation in one patient of Japanese origin with no apparent family history of RP (Invest Ophthalmol Vis Sci 45:4433-4439, 2004). This mutation resulted in a frameshift with loss of the last 28 amino acids of the encoded protein.

The CNGB1 gene encodes the beta subunit of the rod photoreceptor cyclic nucleotide gated channel (CNG) that mediates visual transduction in retinal rods.

Testing Strategy

This test involves bidirectional DNA sequencing of all 32 coding exons and splice sites of the CNGB1 gene. The full coding sequence of each exon plus ~ 20 bp of flanking-coding DNA on either side 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

Patients with AR-RP and heterozygote carriers.

Gene

Official Gene Symbol OMIM ID
CNGB1 600724
Inheritance Abbreviation
Autosomal Dominant AD
Autosomal Recessive AR
X-Linked XL
Mitochondrial MT

Disease

Name Inheritance OMIM ID
Retinitis Pigmentosa 45 613767

Related Tests

Name
Autosomal Recessive Retinitis Pigmentosa Sequencing Panel
Retinitis Pigmentosa (includes RPGR ORF15) Sequencing Panel

CONTACTS

Genetic Counselors
Geneticist
Citations
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.

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.
loading Loading... ×