Residency · Residency · Ophthalmology
Genetic Testing in Ophthalmology: When and How
Introduction
The era of precision medicine has brought genetic testing to the forefront of ophthalmic care. With over 300 genes implicated in inherited retinal dystrophies alone, and growing therapeutic options including gene therapy, accurate molecular diagnosis is increasingly essential. Understanding when to order genetic testing, which tests to select, how to interpret results, and how to counsel patients are core competencies for the modern ophthalmologist.
Indications for Genetic Testing
Inherited Retinal Dystrophies (IRDs)
All patients with suspected IRDs should be offered genetic testing. Essential for gene therapy eligibility (e.g., RPE65-associated retinal dystrophy and voretigene neparvovec) Guides prognosis and natural history predictions. Informs inheritance pattern and recurrence risk counseling. Enables enrollment in gene-specific clinical trials. Examples: retinitis pigmentosa, Stargardt disease, Leber congenital amaurosis, choroideremia, achromatopsia.
Pediatric Ophthalmic Genetics
Retinoblastoma: RB1 germline testing for all bilateral cases, unilateral cases with family history, and young age at presentation. Congenital cataracts, aniridia (PAX6), anterior segment dysgenesis (FOXC1, PITX2) Congenital glaucoma (CYP1B1, LTBP2) Albinism (TYR, OCA2, SLC45A2)
Corneal Dystrophies
TGFBI gene testing for granular, lattice, Reis-Bucklers, and Thiel-Behnke dystrophies. Important for surgical planning (recurrence risk in grafts) Fuchs endothelial dystrophy: TCF4 trinucleotide repeat expansion.
Glaucoma
Juvenile open-angle glaucoma: MYOC (myocilin) gene testing. Primary congenital glaucoma: CYP1B1. Emerging: polygenic risk scores for primary open-angle glaucoma.
Optic Neuropathies
Leber hereditary optic neuropathy (LHON): mitochondrial DNA mutations (m.11778G>A, m.14484T>C, m.3460G>A) Dominant optic atrophy: OPA1 mutations.
Ocular Oncology
BAP1 tumor predisposition syndrome: uveal melanoma, mesothelioma, renal cell carcinoma. RB1 for retinoblastoma (germline vs. somatic) Prognostic genetic testing in uveal melanoma (GEP, chromosome 3 status)
Systemic Conditions with Ocular Manifestations
Marfan syndrome (FBN1): lens subluxation. Homocystinuria (CBS): lens subluxation (inferior) Neurofibromatosis type 1 (NF1): Lisch nodules, optic pathway glioma. Usher syndrome: RP + hearing loss (MYO7A, USH2A, CDH23)
Types of Genetic Tests
Targeted Single-Gene Testing
Tests a specific gene based on strong clinical suspicion. Fast turnaround; lower cost. Example: MYOC for juvenile POAG, CHM for choroideremia with classic phenotype. Limited by inability to detect mutations in other genes.
Gene Panels
Next-generation sequencing (NGS) panels covering multiple genes associated with a phenotype. IRD panels: 200-350+ genes. Corneal dystrophy panels, glaucoma panels, ocular oncology panels. Diagnostic yield for IRDs: 60-70% with current panels. Cost-effective; good balance of breadth and depth. May miss deep intronic variants or structural rearrangements.
Whole Exome Sequencing (WES)
Sequences all protein-coding regions (~20,000 genes) Useful when panel testing is negative or phenotype is atypical. Higher chance of variants of uncertain significance (VUS). May identify novel genes or unexpected diagnoses. Requires bioinformatics expertise for interpretation.
Whole Genome Sequencing (WGS)
Sequences entire genome including non-coding regions. Detects deep intronic variants, structural variants, copy number variants. Most comprehensive but most expensive and data-intensive. Increasingly used in research and becoming more clinically accessible.
| Test Type | Scope | Diagnostic Yield (IRDs) | Best Use Case | Limitation |
|---|---|---|---|---|
| Single-gene testing | 1 gene | Variable | Classic phenotype with known gene | Misses other genes |
| Gene panel (NGS) | 200-350+ genes | 60-70% | Standard first-line for IRDs | May miss non-coding variants |
| Whole exome (WES) | ~20,000 genes | 70-80% | Panel-negative cases | More VUS; higher cost |
| Whole genome (WGS) | Entire genome | Highest | Deep intronic/structural variants | Most expensive; data-intensive |
| Chromosomal microarray | Genome-wide CNVs | Variable | Syndromic conditions | Does not detect point mutations |
| Mitochondrial DNA | mtDNA | High for LHON | Suspected mitochondrial disease | Limited to mtDNA variants |
Chromosomal Microarray
Detects copy number variants (deletions, duplications) Useful for syndromic conditions with suspected genomic rearrangements.
Mitochondrial DNA Testing
Specific testing for LHON and mitochondrial syndromes. Standard NGS panels may not cover mitochondrial genome.
Pre-Test Considerations
Genetic Counseling
Ideally involve a certified genetic counselor or clinical geneticist. Discuss purpose, limitations, possible outcomes, and implications. Address psychological impact: anxiety, guilt, implications for family members. Informed consent: include discussion of incidental findings, VUS, data storage.
Family History
Construct a detailed pedigree (at least 3 generations) Identify affected and unaffected family members. Determine likely inheritance pattern (autosomal dominant, recessive, X-linked, mitochondrial) Consider consanguinity, de novo mutations, variable expressivity, reduced penetrance.
Clinical Phenotyping Before Testing
Detailed ophthalmic examination: fundoscopy, OCT, FAF, ERG, visual fields. Accurate phenotyping improves test interpretation and variant classification. ERG pattern (rod-cone vs. cone-rod) narrows differential significantly.
Interpreting Results
Variant Classification (ACMG Guidelines)
Pathogenic: strong evidence of disease causation; actionable. Likely pathogenic: high probability of disease causation; treat as pathogenic clinically. Variant of uncertain significance (VUS): insufficient evidence; do not use for clinical decision-making. Likely benign: low probability of disease association. Benign: no evidence of disease association.
Challenges in Interpretation
VUS: common finding (up to 30% of results); may be reclassified over time. Phenotype-genotype correlation is essential for proper interpretation. Some genes have variable expressivity (same mutation, different severity) Reduced penetrance: carriers of pathogenic variant may be unaffected. Compound heterozygosity: two different mutations in the same gene (recessive conditions)
Negative Results
Does not exclude a genetic cause; may reflect: Mutations in regions not covered by the test (deep intronic, regulatory) Novel genes not yet identified. Structural variants not detected by standard sequencing. Consider WES/WGS, segregation analysis, or research studies.
Post-Test Management
Positive Result
Confirm genotype-phenotype correlation. Discuss inheritance pattern and recurrence risk. Offer cascade testing to at-risk family members. Assess eligibility for gene-specific therapies (e.g., voretigene neparvovec for RPE65) Enroll in gene-specific natural history studies or clinical trials. Connect with patient advocacy organizations (Foundation Fighting Blindness, etc.)
Carrier Testing and Reproductive Counseling
Carrier testing for at-risk family members (autosomal recessive and X-linked conditions) Prenatal diagnosis options: chorionic villus sampling, amniocentesis. Preimplantation genetic testing (PGT): IVF with embryo screening for known familial mutation. Non-directive counseling: present options without recommending a specific reproductive choice.
Practical Resources
Testing Laboratories and Programs
My Retina Tracker (Foundation Fighting Blindness): free genetic testing program for IRD patients in the US. Blueprint Genetics, GeneDx, Invitae: commercial laboratories offering ophthalmic gene panels. CLIA-certified laboratories required for clinical-grade results. Research-grade testing may require clinical confirmation.
Cost and Insurance
Cost has decreased dramatically (full IRD panels < $250 through some programs) Many insurance plans cover genetic testing when medically indicated. Sponsored testing programs reduce financial barriers.
Registries and Databases
ClinVar: public database of variant classifications. OMIM: Online Mendelian Inheritance in Man. RetNet: Retinal Information Network (retinal disease gene database) Patient registries facilitate clinical trial recruitment.
Key Clinical Pearls
All patients with suspected inherited retinal dystrophies should be offered genetic testing; it is essential for gene therapy eligibility and clinical trial enrollment. Gene panels covering 200-350+ IRD genes achieve a diagnostic yield of 60-70%; negative results do not exclude a genetic etiology. Variants of uncertain significance (VUS) should not be used for clinical decision-making; they may be reclassified as more data become available. Genetic counseling before and after testing is essential to ensure informed consent, proper interpretation, and appropriate family cascade testing.
References
- Stone EM, Andorf JL, Whitmore SS, et al. Clinically focused molecular investigation of 1000 consecutive families with inherited retinal disease. Ophthalmology. 2017;124(9):1314-1331.
- Schneider N, Sundaresan Y, Goonatilake R, et al. Inherited retinal diseases: linking genes, disease-causing variants, and relevant therapeutic modalities. Prog Retin Eye Res. 2022;89:101029.
- Richards S, Aziz N, Bale S, et al. Standards and guidelines for the interpretation of sequence variants (ACMG/AMP). Genet Med. 2015;17(5):405-424.
- Lenassi E, Clayton-Smith J, Douzgou S, et al. Clinical utility of genetic testing in 201 preschool children with inherited eye disorders. Genet Med. 2020;22(4):745-751.