A range of testing methodologies are needed to identify pathogenic changes in the RB1 gene including:
- Sequencing (deep sequencing method is recommended for better detection of mosaic pathogenic variants)
- copy number analysis [e.g. MLPA]
- methylation analysis
- analysis for structural rearrangements/large deletions involving 13q
When no somatic RB1 pathogenic variants are identified in unilateral retinoblastoma under the age of 12 months analysis of amplification of MYCN gene in tumour tissue is recommended. MYCN amplification and somatic RB1 pathogenic variants are mutually exclusiver.
Information about testing and for laboratories is available from:
If a decision is made to test this gene(s) as part of a cancer gene panel, care should be taken to select a panel where the individual genes tested have both clinical validity and clinical utility.
Genetic testing of tumour tissue may be needed to determine heritability and relative recurrence risks. Tumour DNA can be extracted from either fresh frozen tumour or micro-dissected tumour from paraffin blocks.
- In a proband with apparently sporadic (no family history), unilateral, unifocal disease initial testing should ideally occur in tumour tissue seeking to identify two RB1 tumour pathogenic variants. Ideally blood should then be tested to differentiate sporadic unilateral from heritable unilateral disease.Link to UL table.
- In a proband with bilateral or multi-focal retinoblastoma, or a family history of retinoblastoma, initial testing should occur in blood seeking to identify a heritable (germline) RB1 pathogenic variant. If no pathogenic variant is identified testing of tumour tissue should occur to differentiate low level somatic mosaicism from a presumed cryptic heritable RB1 pathogenic variant. Link to BL table.