See Table A. Genes and Databases for chromosome locus and protein.

See Molecular Genetics for information on variants detected in this gene.

Sequence analysis detects variants that are benign, likely benign, of uncertain significance, likely pathogenic, or pathogenic. Variants may include missense, nonsense, and splice site variants and small intragenic deletions/insertions; typically, exon or whole-gene deletions/duplications are not detected. For issues to consider in interpretation of sequence analysis results, click here.

Gene-targeted deletion/duplication analysis detects intragenic deletions or duplications. Methods used may include a range of techniques such as quantitative PCR, long-range PCR, multiplex ligation-dependent probe amplification (MLPA), and a gene-targeted microarray designed to detect single-exon deletions or duplications. Gene-targeted deletion/duplication testing will detect deletions ranging from a single exon to the whole gene; however, breakpoints of large deletions and/or deletion of adjacent genes (e.g., those described by Mitter et al [2011], Castéra et al [2013]) may not be detected by these methods.

Chromosomal microarray analysis (CMA) uses oligonucleotide or SNP arrays to detect genome-wide large deletions/duplications (including RB1) that cannot be detected by sequence analysis. The ability to determine the size of the deletion/duplication depends on the type of microarray used and the density of probes in the 13q14 region. CMA designs in current clinical use target the 13q14 region.

Approximately 6%-8% of individuals with retinoblastoma have a chromosome deletion of 13q14. Such chromosome abnormalities are often associated with developmental delay and birth defects [Mitter et al 2011; Castéra et al 2013; Authors, unpublished data].

Hypermethylation of RB1 promoter (which silences gene expression) is observed in approximately 15% of tumors from individuals with sporadic, unilateral retinoblastoma [Zeschnigk et al 2004; Authors, unpublished data]. In these individuals, analysis of the promoter methylation status in DNA from tumor is needed to identify the two inactive RB1 alleles that triggered tumor development.

Testing for loss of heterozygosity in tumors. Comparative genotyping of polymorphic loci within and flanking RB1 in DNA from peripheral blood and tumor can reveal that loss of the normal allele with (hemizygosity) or without duplication (homozygosity) of the mutated allele initiated the tumor, observed in 60%-70% of tumors from enucleated eyes.

About 1.5% of children with unilateral retinoblastoma and no family history have high-level MYCN amplification on tumor tissue testing but no pathogenic variants leading to inactivation of RB1 [Rushlow et al 2013, Singh et al 2022]. To date, it is not known if all individuals with high-level MYCN amplification in a retinoblastoma and no identified germline RB1 pathogenic variant have non-heritable retinoblastoma [Davies et al 2021].