Retinal Dystrophy Panel

Summary

The Blueprint Genetics Retinal Dystrophy Panel (test code OP0801):

Test Specific Strength

The majority of the X-linked RP is caused by mutations in theRPGR gene, which contains a mutational hotspot at a unique 567-aa exon called ORF15 accounting for two-thirds of all disease-causing mutations. The exon ORF15, however, includes a highly repetitive, purine-rich sequence, which generally performs poorly in NGS-based assays. Blueprint Genetics custom assay has good coverage (>20x) with high mapping rates (mapping quality >20) for 100.0% of the target regions in RPGR gene. Our validation showed high mean coverage of 139X for the RPGR gene. Thus, our NGS Panel is not expected to have major limitations in detecting variants in RPGR gene including ORF15 exon.

ICD codes

Commonly used ICD-10 code(s) when ordering the Retinal Dystrophy Panel

Sample Requirements

• Blood (min. 1ml) in an EDTA tube
• Extracted DNA, min. 2 μg in TE buffer or equivalent
• Saliva (Please see Sample Requirements for accepted saliva kits)

Label the sample tube with your patient's name, date of birth and the date of sample collection.

We do not accept DNA samples isolated from formalin-fixed paraffin-embedded (FFPE) tissue. In addition, if the patient is affected with a hematological malignancy, DNA extracted from a non-hematological source (e.g. skin fibroblasts) is strongly recommended.

Please note that, in rare cases, mitochondrial genome (mtDNA) variants may not be detectable in blood or saliva in which case DNA extracted from post-mitotic tissue such as skeletal muscle may be a better option.

Read more about our sample requirements here.

Please include fundus photographs, electroretinogram (ERG) findings, visual field findings and visual acuity, if available, for expert review and clinical correlation with test results

Subpanel description

This comprehensive panel includes genes from the following panels: Achromatopsia, Macular Dystrophy, Leber Congenital Amaurosis, Congenital Stationary Night Blindness, Flecked Retina Disorders, Vitreoretinopathy, Cone Rod Dystrophy, Retinitis Pigmentosa, Usher Syndrome, Stickler Syndrome, Bardet-Biedl Syndrome, Senior-Loken Syndrome and Joubert Syndrome.

Retinal dystrophies are a broad group of clinically and genetically heterogenous disorders affecting the retina (Reviewed in PMID: 26835369). Common presentations among these disorders include night or colour blindness, tunnel vision and subsequent progression to complete blindness. Vision loss can occur anywhere from early infancy to late adulthood and both stationary and progressive diseases have been described. The inheritance pattern may be autosomal recessive, autosomal dominant or X-linked. Sporadic cases are also observed. Mutations within the same gene have been shown to cause different disease phenotypes, even among affected individuals within the same family highlighting further levels of complexity. Retinal dystrophy can be nonsyndromic or part of a syndrome in which clinical presentations extend to more than the affected retina. Examples of retinal dystrophies associated with syndromic features are Usher syndrome, Bardet-Biedl syndrome, Joubert syndrome, Senior-Loken syndrome, Cohen syndrome and Alström syndrome. For detailed description of different retinal dystrophies, please see the ophthalmology subpanel descriptions.

Genes in the Retinal Dystrophy Panel and their clinical significance

* Some, or all, of the gene is duplicated in the genome. Read more.

# The gene has suboptimal coverage (means <90% of the gene’s target nucleotides are covered at >20x with mapping quality score (MQ>20) reads), and/or the gene has exons listed under Test limitations section that are not included in the panel as they are not sufficiently covered with high quality sequence reads.

The sensitivity to detect variants may be limited in genes marked with an asterisk (*) or number sign (#)

Gene refers to the HGNC approved gene symbol; Inheritance refers to inheritance patterns such as autosomal dominant (AD), autosomal recessive (AR), mitochondrial (mi), X-linked (XL), X-linked dominant (XLD) and X-linked recessive (XLR); ClinVar refers to the number of variants in the gene classified as pathogenic or likely pathogenic in this database (ClinVar); HGMD refers to the number of variants with possible disease association in the gene listed in Human Gene Mutation Database (HGMD). The list of associated, gene specific phenotypes are generated from CGD or Mitomap databases.

Non-coding variants covered by Retinal Dystrophy Panel

Added and removed genes from the panel

Test Strengths

• CAP accredited laboratory
• CLIA-certified personnel performing clinical testing in a CLIA-certified laboratory
• Powerful sequencing technologies, advanced target enrichment methods and precision bioinformatics pipelines ensure superior analytical performance
• Careful construction of clinically effective and scientifically justified gene panels
• Some of the panels include the whole mitochondrial genome (please see the Panel Content section)
• Our Nucleus online portal providing transparent and easy access to quality and performance data at the patient level
• Our publicly available analytic validation demonstrating complete details of test performance
• ~2,000 non-coding disease causing variants in our clinical grade NGS assay for panels (please see ‘Non-coding disease causing variants covered by this panel’ in the Panel Content section)
• Our rigorous variant classification scheme
• Our systematic clinical interpretation workflow using proprietary software enabling accurate and traceable processing of NGS data
• Our comprehensive clinical statements

Test Limitations

• Complex inversions
• Gene conversions
• Balanced translocations
• Some of the panels include the whole mitochondrial genome but not all (please see the Panel Content section)
• Repeat expansion disorders unless specifically mentioned
• Non-coding variants deeper than ±20 base pairs from exon-intron boundary unless otherwise indicated (please see above Panel Content / non-coding variants covered by the panel).

• Low level mosaicism in nuclear genes (variant with a minor allele fraction of 14.6% is detected with 90% probability)
• Stretches of mononucleotide repeats
• Low level heteroplasmy in mtDNA (>90% are detected at 5% level)
• Indels larger than 50bp
• Single exon deletions or duplications
• Variants within pseudogene regions/duplicated segments
• Some disease causing variants present in mtDNA are not detectable from blood, thus post-mitotic tissue such as skeletal muscle may be required for establishing molecular diagnosis.

The sensitivity of this test may be reduced if DNA is extracted by a laboratory other than Blueprint Genetics.

For additional information, please refer to the Test performance section and see our Analytic Validation.

The genes on the panel have been carefully selected based on scientific literature, mutation databases and our experience.

Our panels are sectioned from our high-quality, clinical grade NGS assay. Please see our sequencing and detection performance table for details regarding our ability to detect different types of alterations (Table).

Assays have been validated for various sample types including EDTA-blood, isolated DNA (excluding from formalin fixed paraffin embedded tissue), saliva and dry blood spots (filter cards). These sample types were selected in order to maximize the likelihood for high-quality DNA yield. The diagnostic yield varies depending on the assay used, referring healthcare professional, hospital and country. Plus analysis increases the likelihood of finding a genetic diagnosis for your patient, as large deletions and duplications cannot be detected using sequence analysis alone. Blueprint Genetics’ Plus Analysis is a combination of both sequencing and deletion/duplication (copy number variant (CNV)) analysis.

Performance of Blueprint Genetics high-quality, clinical grade NGS sequencing assay for panels.

Performance of Blueprint Genetics Mitochondrial Sequencing Assay.

Bioinformatics

The target region for each gene includes coding exons and ±20 base pairs from the exon-intron boundary. In addition, the panel includes non-coding and regulatory variants if listed above (Non-coding variants covered by the panel). Some regions of the gene(s) may be removed from the panel if specifically mentioned in the ‘Test limitations” section above. If the test includes the mitochondrial genome the target region gene list contains the mitochondrial genes. The sequencing data generated in our laboratory is analyzed with our proprietary data analysis and annotation pipeline, integrating state-of-the art algorithms and industry-standard software solutions. Incorporation of rigorous quality control steps throughout the workflow of the pipeline ensures the consistency, validity and accuracy of results. Our pipeline is streamlined to maximize sensitivity without sacrificing specificity. We have incorporated a number of reference population databases and mutation databases including, but not limited, to 1000 Genomes Project, gnomAD, ClinVar and HGMD into our clinical interpretation software to make the process effective and efficient. For missense variants, in silico variant prediction tools such as  SIFT, PolyPhen, MutationTaster are used to assist with variant classification. Through our online ordering and statement reporting system, Nucleus, ordering providers have access to the details of the analysis, including patient specific sequencing metrics, a gene level coverage plot and a list of regions with suboptimal coverage (<20X for nuclear genes and <1000X for mtDNA) if applicable. This reflects our mission to build fully transparent diagnostics where ordering providers can easily visualize the crucial details of the analysis process.

Clinical interpretation

We provide customers with the most comprehensive clinical report available on the market. Clinical interpretation requires a fundamental understanding of clinical genetics and genetic principles. At Blueprint Genetics, our PhD molecular geneticists, medical geneticists and clinical consultants prepare the clinical statement together by evaluating the identified variants in the context of the phenotypic information provided in the requisition form. Our goal is to provide clinically meaningful statements that are understandable for all medical professionals regardless of whether they have formal training in genetics.

Variant classification is the corner stone of clinical interpretation and resulting patient management decisions. Our classifications follow the Blueprint Genetics Variant Classification Schemes based on the ACMG guideline 2015. Minor modifications were made to increase reproducibility of the variant classification and improve the clinical validity of the report. Our experience with tens of thousands of clinical cases analyzed at our laboratory allowed us to further develop the industry standard.

The final step in the analysis is orthogonal confirmation. Sequence and copy number variants classified as pathogenic, likely pathogenic and variants of uncertain significance (VUS) are confirmed using bi-directional Sanger sequencing by orthogonal methods such as qPCR/ddPCR when they do not meet our stringent NGS quality metrics for a true positive call.

Our clinical statement includes tables for sequencing and copy number variants that include basic variant information (genomic coordinates, HGVS nomenclature, zygosity, allele frequencies, in silico predictions, OMIM phenotypes and classification of the variant). In addition, the statement includes detailed descriptions of the variant, gene and phenotype(s) including the role of the specific gene in human disease, the mutation profile, information about the gene’s variation in population cohorts and detailed information about related phenotypes. We also provide links to the references, abstracts and variant databases used to help ordering providers further evaluate the reported findings if desired. The conclusion summarizes all of the existing information and provides our rationale for the classification of the variant.

Identification of pathogenic or likely pathogenic variants in dominant disorders or their combinations in different alleles in recessive disorders are considered molecular confirmation of the clinical diagnosis. In these cases, family member testing can be used for risk stratification. We do not recommend using variants of uncertain significance (VUS) for family member risk stratification or patient management. Genetic counseling is recommended.

Our interpretation team analyzes millions of variants from thousands of individuals with rare diseases. Our internal database and our understanding of variants and related phenotypes increases with every case analyzed. Our laboratory is therefore well-positioned to re-classify previously reported variants as new information becomes available. If a variant previously reported by Blueprint Genetics is re-classified, our laboratory will issue a follow-up statement to the original ordering health care provider at no additional cost.

Recommendations on Clinical Assessment of Patients with Inherited Retinal Degenerations – 2016