Introduction of a Variant Classification System for Analysis of Genotype-Phenotype Relationships in Heritable Retinoblastoma

Retinoblastoma caused by an RB1 variant with unusually low penetrance in a Danish family

Retinoblastoma is the most common eye cancer in children. It is caused by pathogenic alterations of both alleles of the tumor suppressor gene RB1. In heritable retinoblastoma, a constitutional RB1 variant predisposes the cells to tumor formation, and loss of the other allele is a prerequisite for the development of retinoblastoma. Heritable retinoblastoma is inherited in an autosomal dominant manner; however, the majority of cases are the result of a de novo pathogenic RB1 variant. Penetrance is usually high (>90%), but with marked inter-familial variability. In some families, penetrance is incomplete and family members who develop tumors tend to remain unilaterally affected. Moreover, some families with low penetrance also show a parent-of-origin effect. We describe a patient with unilateral retinoblastoma caused by a previously unreported likely pathogenic RB1 variant (c.1199T>C) that disrupts a highly conserved amino acid residue within the A-box functional domain. Segregation analysis showed that the variant had unusually low penetrance as nine non-affected family members carried the same variant. We emphasize the use of genetic analysis on tumor DNA for classifying the RB1 variant, and underline the challenges in clinical management and counseling of families carrying the specific RB1 variant.

'It's not meant to be for life, but it carries on': a qualitative investigation into the psychosocial needs of young retinoblastoma survivors

OBJECTIVE AND DESIGN

Retinoblastoma (Rb) is a rare childhood eye cancer, with 45% of individuals impacted by heritable disease and the remainder impacted non-heritably. The condition can leave survivors with life-long psychological and social challenges. This qualitative study examined the psychosocial needs of teenagers and young adults living beyond Rb.

SETTING

A qualitative, exploratory study was conducted using focus groups with teenagers and interviews with young adults. Participants were recruited via the Childhood Eye Cancer Trust and the two national Rb treatment centres in the UK. Reflexive thematic analysis was used to analyse data using exploratory and inductive methods.

PARTICIPANTS

32 young survivors of Rb (10 heritable, 21 non-heritable, 1 unknown; 23 unilateral, 9 bilateral) aged between 13 and 29 years (12 male, 20 female).

RESULTS

Data were rich and spanned the life course: three key themes were generated, containing eight subthemes. Theme 1 describes participants' experiences of childhood and trauma, including survivor guilt, memories from treatment and impact on personality. Theme 2 focuses on the challenges of adolescence, including the psychological impact of Rb, the impact on identity, and the sense of normality and adaptation to late effects. The third theme considered adulthood and the development of acceptance, a state of being widely considered unachievable during childhood, as well as the 'work' needed to feel supported, including seeking out information, peer support and therapeutic strategies.

CONCLUSIONS

This study provides in-depth insight into the experiences of life beyond Rb. Findings highlight the need for specific psychosocial interventions informed by codesign.

Familial retinoblastoma: variations in clinical presentation and management based on paternal versus maternal inheritance

BACKGROUND

Several studies have demonstrated the effect of parent-of-origin on retinoblastoma penetrance. The purpose of the current study was to assess differences in clinical presentation of paternally versus maternally inherited retinoblastoma.

METHODS

The clinical records of all children with familial retinoblastoma treated on a tertiary Ocular Oncology Service between December 1975 and May 2020 were reviewed retrospectively.

RESULTS

A total of 179 patients with familial retinoblastoma were included. Paternal inheritance (PI) was identified in 109 (61%) patients and maternal inheritance (MI) in 70 patients (39%). A comparison (PI vs MI) revealed PI patients were older at presentation (57.2 vs 24.4 months [P = 0.002]) with no difference in patient sex (53% females vs 57% males [P = 0.606]) or number of family members affected (3.2 vs 3.0 family members [P = 0.255]). PI patients had more advanced classification according to the International Classification of Retinoblastoma (ICRB) (group E: 31% vs 8% [P = 0.012)] and greater largest tumor in basal diameter (9.0 vs 6.2 mm [P = 0.040]) and thickness (5.6 vs 4.0 mm [P = 0.038]); they were also less likely to be located in the macula (40% vs 60% [P = 0.004]). There was no difference in tumor laterality (69% vs 64% bilaterality [P = 0.530]). PI patients required enucleation more frequently (34% vs 14% [P = 0.007]). There was no difference in need for plaque radiotherapy (P = 0.86) or chemotherapy (P = 0.85). One PI patient developed metastatic retinoblastoma, and there were no retinoblastoma-related deaths.

CONCLUSIONS

Patients with paternally inherited retinoblastoma presented at an older age, with larger, more peripheral tumors and more advanced ICRB group, and were more likely to require enucleation compared to those with maternally inherited retinoblastoma.

An overview of RB1 transcript alterations detected during retinoblastoma genetic screening

Identification of pathogenic RB1 variants aids in the clinical management of families with retinoblastoma. We routinely screen DNA for RB1 variants, but transcript analysis can also be used for variant screening, and to help decide variant pathogenicity. DNA was screened by conformation analysis followed by Sanger sequencing. Large deletion/insertions were detected by polymorphism analysis, MLPA and quantitative-PCR. Methylation-specific PCR was used to detect hypermethylation. RNA screening was performed when a DNA pathogenic variant was missing, or to determine effects on splicing.Two hundred and thirteen small coding variants were predicted to affect splicing in 207 patients. Splice donor (sd) variants were nearly twice as frequent as splice acceptor (sa) with the most affected positions being sd + 1 and sa-1. Some missense and nonsense codons altered splicing, while some splice consensus variants did not. Large deletion/insertions can disrupt splicing, but RNA analysis showed that some of these are more complex than indicated by DNA testing. RNA screening found pathogenic variants in 53.8% of samples where DNA analysis did not. RB1 splicing is altered by changes at consensus splice sites, some missense and nonsense codons, deep intronic changes and large deletion/insertions. Common alternatively spliced transcripts may complicate analysis. An effective molecular screening strategy would include RNA analysis to help determine pathogenicity.

Special Issue of Cancers: "Retinoblastoma: Current Challenges and Promising New Approaches"

Despite being a rare pediatric cancer arising in the developing retina from red/green cone precursors, retinoblastoma is the most common eye cancer worldwide and occupies an emblematic position in oncology and human genetics for the following reasons:-Historically, the discovery of RB1 and the recessive nature of its mutations led to the prototypic description of anti-oncogenes or tumor suppressor genes [...].

Germline RB1 Mutation in Retinoblastoma Patients: Detection Methods and Implication in Tumor Focality

Purpose

The study aimed to generate a stepwise method to reduce the workload of full-scale RB1 sequencing for germline mutation screening in retinoblastoma (RB) patients. The implication of germline mutation in tumor focality was also determined in this study.

Methods

A stepwise method was created on the basis of "hotspot" exons analyzed using data on germline RB1 mutation in the RB1-Leiden Open Variation Database and then tested for mutation screening in the blood DNA of 42 patients with RB. The method was compared with the clinical next-generation sequencing (NGS) panel in terms of sequencing outcomes. The germline RB1 mutation was examined in association with multifocality in RB.

Results

Germline RB1 mutation was identified in 61% of all bilateral cases in the first step of the 3 stepwise method and in 78% and 89% for the two and three steps combined, respectively. NGS detected a mosaic variant of RB1 that was not detected by the first two steps and increased the sensitivity from 78% to 83%. Analysis of the relationship between mutation status and tumor focality indicated that multifocality in RB was dependent on germline RB1 mutation, confirming a higher tendency to have a germline RB1 mutation in patients with multifocal RB.

Conclusions

A 3 stepwise method reduces the workload needed for sequencing of the RB1 for bilateral cases. NGS outweighs conventional sequencing in terms of the identification of germline mosaic variants. Multifocal tumors in RB may be used to presume germline mutation.

Translational Relevance

The presence of "hotspot" exons of germline RB1 mutation in bilateral cases facilitates a mutation screening. However, when genetic testing is not available, multifocality in RB regardless of tumor laterality is predictive of germline RB1 mutation.