Detection of mosaic RB1 mutations in families with retinoblastoma

Re-envisioning genetic predisposition to childhood and adolescent cancers

Although cancer is rare in children and adolescents, it remains a leading cause of death within this age range, and genetic predisposition is the main known risk factor. Since the discovery of retinoblastoma-predisposing RB1 pathogenic germline variants in 1985, several additional high-penetrance cancer predisposition genes (CPGs) have been identified. Although few clinically recognizable genetic conditions display moderate cancer phenotypes, burden testing has revealed low-to-moderate penetrance CPGs. In addition to germline pathogenic variants in CPGs, postzygotic somatic mosaic CPG pathogenic variants acquired during embryonic development are increasingly recognized as factors that predispose children and adolescents to malignancies. Genome-wide association studies of various childhood and adolescent cancer types have identified some common low-risk cancer susceptibility alleles. Although the clinical utility of polygenic risk scores is currently limited in children and adolescents, polygenic risk scores developed for adults can predict subsequent cancer risks in childhood and adolescent cancer survivors. In this Review, I describe our current knowledge of genetic predisposition to childhood and adolescent cancers. Survival rates in children and adolescents with cancer and CPGs are often poor, necessitating better integration of genomic testing into clinical care to improve cancer prevention, surveillance and therapies.

A family-based approach to cascade genetic testing in a pediatric cancer genetics clinic

Hereditary cancer predisposition disorders account for up to 10% of all pediatric cancers. Genetic counseling for families of the proband includes risk assessment and recommendations for cascade genetic testing for parents and siblings, but there is no standardized method for cascade testing in place resulting in variability in how clinics approach cascade genetic testing. We explored the uptake and outcomes associated with a family-based approach to cascade testing, for non-syndromic cancer predisposition disorders, at a pediatric cancer genetics clinic serving an ethnically diverse patient population. A retrospective chart review was conducted to evaluate test uptake in the parents and siblings of 106 pediatric probands. The study included 99 mothers, 97 fathers, 116 full siblings, and 53 half siblings who were recommended testing due to genetic risk. Of these relatives, 156 (43%) had documentation of completed cascade testing within twenty-four months after the proband's result disclosure. Completion of cascade testing varied by the type of family member and degree of relatedness. 41% of mothers (41/99) were tested in comparison to 26% of fathers (26/97) and 70.6% of full siblings (82/116) were tested compared to 13.2% of half siblings (7/53). Statistical analysis using chi-squared tests revealed that siblings were more likely to have completed testing than parents (p < 0.001). Furthermore, amongst parents, mothers were more likely to complete testing than fathers (p = 0.03) and amongst siblings, full siblings were more likely to complete testing than half siblings (< 0.001). The proband's age (p = 0.008), parents' preferred language (p = 0.002), and interpreter use during visit (p = 0.004) were the factors associated with differences in test uptake amongst siblings, whereas the proband's race/ethnicity (p = 0.019) was the only factor associated with differences in test uptake amongst parents. The most common barriers noted in charts for lack of test completion included country of residence, lack of insurance, and loss to follow-up. In conclusion, we found that test uptake differed significantly among relatives of a proband with siblings being more likely to test than parents. We also found differences in the demographic and clinical factors associated with test uptake in parents and siblings. Future studies need to validate these differences and further explore the underlying cause of variation in test uptake among relatives.

Postzygotic mosaicism of SMARCB1 variants in patients with rhabdoid tumors: A not-so-rare condition exposing to successive tumors

BACKGROUND

Rhabdoid tumors (RT) are aggressive, rare tumors predominantly affecting young children, characterized by biallelic SMARCB1 gene inactivation. While most SMARCB1 alterations are acquired de novo, a third of cases exhibit germline alterations, defining Rhabdoid Tumors Predisposition Syndrome. With the increased sensitivity of next-generation sequencing (NGS), mosaicisms in genes linked to genetic diseases are more detectable. This study focuses on exploring SMARCB1 germline alterations, notably mosaicism in blood samples of children with RT and in parents, using a custom NGS panel.

METHODS

A cohort of 280 children and 140 parents with germline analysis was studied. Germline DNA from 111 children with RT and 32 parents were reanalyzed with a custom NGS panel with 1500X average depth targeting the SMARCB1 gene to identify intragenic variants not detected with conventional low-sensitivity methods. Follow-up data was obtained for 77 patients.

RESULTS

Nine previously undetected mosaicism cases were identified, totaling 17/280 patients with a mosaic variant (6.1%) in the cohort, with variant allele frequencies between 0.9% and 33%, thus highlighting the prior underestimation of its prevalence. Follow-up data showed that 4 out of 7 survivors with mosaic variants developed distinct novel tumors, 2 sharing SMARCB1 alterations with the initial tumor, emphasizing the potential clinical impact of SMARCB1 mosaicism.

CONCLUSIONS

The hitherto underestimated rate of SMARCB1 mosaicism in RT underscores the need for optimized genetic counseling and oncological monitoring. The findings have significant medical implications, considering the dire prognosis of RT.

Mutational analysis of the RB1 gene in patients with unilateral retinoblastoma

Purpose

Retinoblastoma, a childhood cancer originating in the retina, is primarily attributed to pathogenic RB1 mutations The aim of this study is to conduct a mutational analysis of the RB1 gene in cases of unilateral Retinoblastoma among individuals within the Jordanian population.

Methods

In this study, the peripheral blood of 50 unilateral Rb patients was collected, genomic DNA was extracted, and mutations were identified using Next Generation Sequencing (NGS) analysis.

Results

In this cohort of 50 unrelated patients with unilateral Rb, the median age at diagnosis was eight months (mean, 12 months; range; 2 weeks to 54 months). Twenty-eight (56%) were males, 29 (58%) had the disease in the right eye, 3 (6%) had a positive family history of Rb, and 20 (40%) were diagnosed within the first year of life. RB1 gene pathogenic mutations were detected in 14 out of 50 (28%) patients, indicating germline disease. Among unilateral non-familial cases, 11 out of 47 (23%) were found to have germline RB1 mutations. Overall, five (36%) of the germline cases had the same mutation detected in one of the parents consistent with an inherited disease (four (80%) were of paternal origin); 3 (60%) of these had affected carrier parent, two (40%) had an unaffected carrier parent. Nine (64%) patients had the nonsense mutation, and six (43%) had the mosaic mutation. The significant prognostic factors for positive genetic testing were positive family history (p = 0.018) and age at diagnosis less than 12 months (p = 0.03). At a median of 54 months follow-up, two (4%) patients were dead from distant metastasis. The overall eye salvage rate was 44% (n = 22/50) eyes; 100% for groups A, B, and C, 60% for group D, and none for group E eyes. There was no correlation between the presence of germline mutation and outcome in terms of eye salvage, metastasis, and survival.

Conclusion

In this study, 28% of patients with unilateral Rb had germline RB1 mutations, of which 43% were inherited, and one-third presented beyond their first year of life. Therefore, molecular screening is critical for genetic counseling regarding the risk for inherited Rb in unilateral cases, including those with no family history, regardless of the age at diagnosis. However, germline mutations did not appear to significantly predict patient outcomes regarding eye salvage, metastasis, and survival.

Development and preliminary evaluation of a genetics education booklet for retinoblastoma

BACKGROUND

Parents and survivors of retinoblastoma often hold misconceptions about the disease and desire more extensive and detailed information about its genetic nature. The aim of this study was to co-develop and evaluate a genetic education booklet for retinoblastoma.

METHODS

A human-centered design approach was employed, in which the study team consulted with clinician and patient knowledge user groups to design, produce, and refine an educational booklet. Over three phases of consultation, the study team met with each knowledge user group to review booklet prototypes and collect feedback for its further refinement. A preliminary evaluation using quantitative and qualitative methods was completed with six mothers of children with retinoblastoma.

RESULTS

The iterative, phased design process produced an educational booklet rich in images and stories, with complex genetic topics described in simplified terms. The preliminary evaluation showed an average improvement in knowledge between pre- and post-test questionnaire of 10%. Participants were satisfied with content and comprehensiveness of the information included in the booklet.

CONCLUSION

A novel educational tool for families affected by retinoblastoma was developed through collaboration with health care and patient knowledge users. Preliminary evaluation results indicate it is feasible to implement and study the booklet in a prospective, pragmatic trial to evaluate its efficacy.

Tumor-Agnostic Therapy-The Final Step Forward in the Cure for Human Neoplasms?

Cancer accounted for 10 million deaths in 2020, nearly one in every six deaths annually. Despite advancements, the contemporary clinical management of human neoplasms faces a number of challenges. Surgical removal of tumor tissues is often not possible technically, while radiation and chemotherapy pose the risk of damaging healthy cells, tissues, and organs, presenting complex clinical challenges. These require a paradigm shift in developing new therapeutic modalities moving towards a more personalized and targeted approach. The tumor-agnostic philosophy, one of these new modalities, focuses on characteristic molecular signatures of transformed cells independently of their traditional histopathological classification. These include commonly occurring DNA aberrations in cancer cells, shared metabolic features of their homeostasis or immune evasion measures of the tumor tissues. The first dedicated, FDA-approved tumor-agnostic agent's profound progression-free survival of 78% in mismatch repair-deficient colorectal cancer paved the way for the accelerated FDA approvals of novel tumor-agnostic therapeutic compounds. Here, we review the historical background, current status, and future perspectives of this new era of clinical oncology.

Impact of RB1 gene screening from blood collected on a single day from 411 family members of 113 Retinoblastoma survivors in India

OBJECTIVES

To analyse the profile and implication of genetic testing in a cohort of retinoblastoma (RB) patients and their families conducted on a single day during World Retinoblastoma Awareness Week 2017.

METHODS

Retrospective analysis of blood samples were collected from 411 subjects, including 113 probands at a camp organised for RB awareness and were analysed for RB1 mutations by Sanger sequencing and Multiplex Ligation-dependent Probe Amplification (MLPA). If germline mutations were detected, the parents and siblings of the proband were tested for the same mutation.

RESULTS

Germline RB1 mutations were identified in 61/113(54%) probands with a mutation detection rate of 96% (47/49) and 22% (14/64) for bilateral and unilateral RB, respectively. Ten novel pathogenic mutations were identified. Splice mutation was most common (31%) followed by nonsense mutation (26%). The mean age at RB diagnosis was significantly lower in patients having germline RB1 mutation (mean 10.7 months ±2.5) compared to those without (mean 27.2 months ±6.5) (p = <0.0001). Parental transmission of the mutant allele was detected in 15/61(25%) cases of which 11(18%) parents were unaffected indicating incomplete penetrance. The origin of the variant allele was both paternal (n = 7) and maternal (n = 4) wherein 5 were bilateral and 6 unilateral.

CONCLUSIONS

The detection of a germline mutation impacts the proband and family members due to its implications on change in prognosis, frequency of subsequent evaluations, screening for ocular and non-ocular cancers, and surveillance of family and future progeny.

Etiology including epigenetic defects of retinoblastoma

Retinoblastoma (RB), originating from the developing retina, is an aggressive intraocular malignant neoplasm in childhood. Biallelic loss of RB1 is conventionally considered a prerequisite for initiating RB development in most RB cases. Additional genetic mutations arising from genome instability following RB1 mutations are proposed to be required to promote RB development. Recent advancements in high throughput sequencing technologies allow a deeper and more comprehensive understanding of the etiology of RB that additional genetic alterations following RB1 biallelic loss are rare, yet epigenetic changes driven by RB1 loss emerge as a critical contributor promoting RB tumorigenesis. Multiple epigenetic regulators have been found to be dysregulated and to contribute to RB development, including noncoding RNAs, DNA methylations, RNA modifications, chromatin conformations, and histone modifications. A full understanding of the roles of genetic and epigenetic alterations in RB formation is crucial in facilitating the translation of these findings into effective treatment strategies for RB. In this review, we summarize current knowledge concerning genetic defects and epigenetic dysregulations in RB, aiming to help understand their links and roles in RB tumorigenesis.

Clinical analysis of 2790 children with retinoblastoma: a single-center experience in China

BACKGROUND

In this study, we aimed to analyze the clinical characteristics and prognosis of children with retinoblastoma (RB) in a single center in China with a large sample collection spanning 17 years.

METHODS

The clinical data of 2790 children with RB treated in Beijing Tongren Hospital from 2005 to 2021 were collected, and a retrospective analysis was conducted.

RESULTS

The median age of the participants was 28.3 months. There were 3624 affected eyes, 12.4% of which were in groups A-C, 67.1% in groups D-E and 16.2% were not specified. The primary symptom observed in most cases was a white pupil, accounting for 66.5%, followed by strabismus (12.8%). The median follow-up time was 59.7 months. The enucleation rate was 71.3% (703/986) in a single left eye and 72.5% (702/968) in a single right eye. The overall survival (OS) rate was 95.8% (2444/2552) because 237 patients dropped out, and 109 died. Kaplan‒Meier survival analysis showed that the median survival time (MST) was 125.92 months [95% confidence interval (CI) = 124.83-127.01]. Cox multivariate survival analysis showed that trilateral RB (P = 0.017), metastasis site (P = 0.001), and combined distant tissue metastasis (P = 0.001) were independent prognostic factors for RB. The OS of 44 cases of familial RB was 93.2% (41/44), with an MST of 80.62 months (95% CI = 67.70-93.54).

CONCLUSIONS

The timing of eye protection treatment and enucleation should be comprehensively judged to avoid worsening prognosis due to operation time delay. More importantly, the promotion and popularization of diagnosis and treatment technologies are necessary to further improve RB prognosis.

Genetics in ophthalmology: molecular blueprints of retinoblastoma

This review presents current knowledge on the molecular biology of retinoblastoma (RB). Retinoblastoma is an intraocular tumor with hereditary and sporadic forms. 8,000 new cases of this ocular malignancy of the developing retina are diagnosed each year worldwide. The major gene responsible for retinoblastoma is RB1, and it harbors a large spectrum of pathogenic variants. Tumorigenesis begins with mutations that cause RB1 biallelic inactivation preventing the production of functional pRB proteins. Depending on the type of mutation the penetrance of RB is different. However, in small percent of tumors additional genes may be required, such as MYCN, BCOR and CREBBP. Additionally, epigenetic changes contribute to the progression of retinoblastoma as well. Besides its role in the cell cycle, pRB plays many additional roles, it regulates the nucleosome structure, participates in apoptosis, DNA replication, cellular senescence, differentiation, DNA repair and angiogenesis. Notably, pRB has an important role as a modulator of chromatin remodeling. In recent years high-throughput techniques are becoming essential for credible biomarker identification and patient management improvement. In spite of remarkable advances in retinoblastoma therapy, primarily in high-income countries, our understanding of retinoblastoma and its specific genetics still needs further clarification in order to predict the course of this disease and improve therapy. One such approach is the tumor free DNA that can be obtained from the anterior segment of the eye and be useful in diagnostics and prognostics.

Spectrum and tissue distribution of RB1 pathogenic alleles in mosaic retinoblastoma patients

To characterize the spectrum of mosaic RB1 pathogenic alleles and map the distribution of mutant cells in available tissues from mosaic patients. Next-generation sequencing was performed on blood samples from 263 retinoblastoma families to identify mosaic RB1 variant alleles. A variety of available tissues were sampled to determine tissue distribution and fraction of mutant cells in five mosaic patients who consented to participate in mosaic pathogenic allele research. Twelve identified mosaic RB1 variants were all "null" pathogenic alleles and displayed reduced expressivity. The use of next-generation deep sequencing increased the sensitivity of mosaicism detection to 0.03% in the case of tissue DNA. In the five mosaic participants, we observed coherent but uneven, bilateral asymmetrical distribution of mutant cells across various tissues. They all carried early-embryonic mosaic pathogenic alleles and had significantly higher variant fractions in blood than in other tissues. Variant fractions of ipsilateral tissue samples were not concordant higher or lower compared with the contralateral side. Only ipsilateral conjunctival and oral epithelial cells showed concordance in mosaicism levels. No associations were observed between the laterality of affected eyes and variant fractions of any tissue type. NGS allows the detection of low-level mosaicism. Mosaic RB1 pathogenic alleles are prone to occur at very early stages of human embryonic development. With respect to genetic counseling, risk prediction should take into account unrecognized mosaicism. The underlying tissue distribution patterns of mosaic RB1 variant alleles remain to be determined.

Mosaicism in Tumor Suppressor Gene Syndromes: Prevalence, Diagnostic Strategies, and Transmission Risk

A mosaic state arises when pathogenic variants are acquired in certain cell lineages during postzygotic development, and mosaic individuals may present with a generalized or localized phenotype. Here, we review the current state of knowledge regarding mosaicism for eight common tumor suppressor genes-NF1, NF2, TSC1, TSC2, PTEN, VHL, RB1, and TP53-and their related genetic syndromes/entities. We compare and discuss approaches for comprehensive diagnostic genetic testing, the spectrum of variant allele frequency, and disease severity. We also review affected individuals who have no mutation identified after conventional genetic analysis, as well as genotype-phenotype correlations and transmission risk for each tumor suppressor gene in full heterozygous and mosaic patients. This review provides new insight into similarities as well as marked differences regarding the appreciation of mosaicism in these tumor suppressor syndromes.

Advances in biomaterials for the treatment of retinoblastoma

Retinoblastoma is the most common primary intraocular malignancy in children. Although traditional chemotherapy has shown some success in retinoblastoma management, there are several shortcomings to this approach, including inadequate pharmacokinetic parameters, multidrug resistance, low therapeutic efficiency, nonspecific targeting, and the need for adjuvant therapy, among others. The revolutionary developments in biomaterials for drug delivery have enabled breakthroughs in cancer management. Today, biomaterials are playing a crucial role in developing more efficacious retinoblastoma treatments. The key goal in the evolution of drug delivery biomaterials for retinoblastoma therapy is to resolve delivery-associated obstacles and lower nonlocal exposure while ameliorating certain adverse effects. In this review, we will first delve into the historical perspective of retinoblastoma with a focus on the classical treatments currently used in clinics to enhance patients' quality of life and survival rate. As we move along, we will discuss biomaterials for drug delivery applications. Various aspects of biomaterials for drug delivery will be dissected, including their features and recent advances. In accordance with the current advances in biomaterials, we will deliver a synopsis on the novel chemotherapeutic drug delivery strategies and evaluate these approaches to gain new insights into retinoblastoma treatment.

Somatic mosaics in hereditary tumor predisposition syndromes

Historically, it is estimated that 5-10% of cancer patients carry a causative genetic variant for a tumor predisposition syndrome. These conditions have high clinical relevance as they are actionable regarding risk-specific surveillance, predictive genetic testing, reproductive options, and - in some cases - risk reducing surgery or targeted therapy. Every individual is born with on average 0.5-1 exonic mosaic variants prevalent in single or multiple tissues. Depending on the tissues affected, mosaic conditions can abrogate the clinical phenotype of a tumor predisposition syndrome and can even go unrecognized, because it can be impossible or difficult to detect them with routine genetic testing in blood/leucocytes. On the other hand, it is estimated that at least 4% of presumed de novo variants are the result of low-level mosaicism (variant allele frequency <10%) in a parent, while around 7% are true mosaic variants with a higher variant allele frequency, which can sometimes be confused for heterozygous variants. Clonal hematopoiesis however can simulate a mosaic tumor predisposition in genetic diagnostics and has to be taken into account, especially for TP53 variants. Depending on the technique, variant allele frequencies of 2-3% can be detected for single nucleotide variants by next generation sequencing, copy number variants with variant allele frequencies of 5-30% can be detected by array-based technologies or MLPA. Mosaic tumor predisposition syndromes are more common than previously thought and may often remain undiagnosed. The clinical suspicion and diagnostic procedure for several cases with mosaic tumor predisposition syndromes are presented.

Molecular alterations in retinoblastoma beyond RB1

Retinoblastoma is the most common malignant ocular tumor in children. Although RB1 alterations are most frequently involved in the etiology of retinoblastoma, candidate driver events and somatic alterations leading to cell transformation, tumor onset and progression remain poorly understood. In this study, we identified novel genomic alterations in tumors with a panel of 160 genes. Sanger sequencing and Multiplex Ligation-dependent Probe Amplification (MLPA) were initially performed for identifying patients without apparent RB1 alterations in blood DNA. Subsequently, NGS analyses of 24 paired (blood/tumor) samples of these patients were carried out for identifying somatic mutations and copy number variation in RB1 and other 159 genes. One novel pathogenic RB1 mutation and seven novel VUS were identified as well as 90 novel pathogenic mutations in 61 other genes. Twenty-three genes appeared exclusively mutated in tumors without altered RB1 alleles and three frequently affected biological pathways while five other tumors did not show pathogenic RB1 alterations or SNV/indels in 159 other genes. Curiously, deletion of GATA2, AKT1, ARID1A, DNMT3A, MAP2K2, MEN1, MTOR, PTCH1 and SUFU (in homo- or heterozygosity) were exclusively found in these tumors when compared to those with any pathogenic alterations, probably indicating genes that might be essential for the development of retinoblastoma regardless of a functional RB1. Identification of genes associated with retinoblastoma will contribute to understanding presently unknown aspects of this malignancy, which might be essential for its initiation and progression, as well as providing valuable molecular markers.

Retinoblastoma genetics screening and clinical management

BACKGROUND

India accounts for 20% of the global retinoblastoma (RB) burden. However, the existing data on RB1 gene germline mutations and its influence on clinical decisions is minimally explored.

METHODS

Fifty children with RB underwent complete clinical examination and appropriate multidisciplinary management. Screening of germline RB1 gene mutations was performed through next-generation sequencing and Multiplex Ligation-dependent Probe Amplification (MLPA) analysis. The mutation and non-mutation groups were compared for clinical parameters especially severity, progression and recurrence.

RESULTS

Twenty-nine patients had bilateral RB (BLRB) and 21 had unilateral RB (ULRB). The genetic analysis revealed 20 RB1 variations in 29 probands, inclusive of 3 novel mutations, known 16 mutations and heterozygous whole gene deletions. The mutation detection rate (MDR) was 86.2% in BLRB and 19% in ULRB. Associations of disease recurrence (p = 0.021), progression (p = 0.000) and higher percentage of optic nerve invasion, subretinal seeds and high-risk pathological factors were observed in the mutation group. Clinical management was influenced by the presence of germline mutations, particularly while deciding on enucleation, frequency of periodic follow up and radiotherapy.

CONCLUSIONS

We identified novel RB1 mutations, and our mutation detection rate was on par with the previous global studies. In our study, genetic results influenced clinical management and we suggest that it should be an essential and integral component of RB-care in India and elsewhere.

Clinical evaluation of RB1 genetic testing reveals novel mutations in Vietnamese patients with retinoblastoma

Clinical evaluation of the genetic testing strategy is essential for ensuring the correct determination of mutation carriers. The current study retrospectively analyzed genetic and clinicopathological data from 62 Vietnamese patients with retinoblastoma (RB) referred to the Vinmec Hi-Tech Center for RB transcriptional corepressor 1 (RB1) genetic testing between 2017 and 2019. The present study aimed to evaluate the sensitivity of the Next Generation Sequencing (NGS) method to identify novel RB1 mutations, and to consider using age at diagnosis as a risk factor. Genomic DNA was analyzed with custom panel based targeted NGS. NGS was performed on the Beijing Genomics Institute (BGI) sequencing platform, and pathogenic or likely pathogenic variants were confirmed by Sanger sequencing, quantitative PCR (qPCR) or Multiplex Ligation-dependent Probe Amplification assay (MLPA). Constitutional RB1 variants were identified in 100% (25/25) of the bilateral cases, while several common previously reported RB1 mutations were also recorded. In addition, in Vietnamese patients with RB, nine novel RB1 mutations were identified. Children aged between 0-36 months were more likely to be RB1 carriers compared with those aged >36 months. The current findings indicated that the NGS method implemented in the Vinmec Hi-Tech Center was highly accurate, and age at diagnosis may be used to assess the risk of hereditary RB. Furthermore, the newly identified RB1 mutations may provide additional data to improve the current understanding of the mechanisms underlying RB1 inactivation and the development of rapid assays for detecting RB1 mutations. Overall, the present study suggested that NGS may be applied for detecting germline RB1 mutations in routine clinical practice.

The Impact of Cell-Free DNA Analysis on the Management of Retinoblastoma

Retinoblastoma is a childhood eye cancer, mainly caused by mutations in the RB1 gene, which can be somatic or constitutional. Unlike many other cancers, tumour biopsies are not performed due to the risk of tumour dissemination. As a result, until recently, somatic genetic analysis was only possible if an affected eye was removed as part of a treatment. Several recent proof of principle studies have demonstrated that the analysis of tumour-derived cell-free DNA, either obtained from ocular fluid or blood plasma, has the potential to advance the diagnosis and influence the prognosis of retinoblastoma patients. It has been shown that a confirmed diagnosis is possible in retinoblastoma patients undergoing conservative treatment. In vivo genetic analysis of retinoblastoma tumours is also now possible, allowing the potential identification of secondary genetic events as prognostic biomarkers. In addition, noninvasive prenatal diagnosis in children at risk of inheriting retinoblastoma has been developed. Here, we review the current literature and discuss the potential impact of cell-free DNA analysis on both the diagnosis and treatment of retinoblastoma patients and their families.

Whole-Genome Sequencing of Retinoblastoma Reveals the Diversity of Rearrangements Disrupting RB1 and Uncovers a Treatment-Related Mutational Signature

The development of retinoblastoma is thought to require pathological genetic changes in both alleles of the RB1 gene. However, cases exist where RB1 mutations are undetectable, suggesting alternative pathways to malignancy. We used whole-genome sequencing (WGS) and transcriptomics to investigate the landscape of sporadic retinoblastomas derived from twenty patients, sought RB1 and other driver mutations and investigated mutational signatures. At least one RB1 mutation was identified in all retinoblastomas, including new mutations in addition to those previously identified by clinical screening. Ten tumours carried structural rearrangements involving RB1 ranging from relatively simple to extremely complex rearrangement patterns, including a chromothripsis-like pattern in one tumour. Bilateral tumours obtained from one patient harboured conserved germline but divergent somatic RB1 mutations, indicating independent evolution. Mutational signature analysis showed predominance of signatures associated with cell division, an absence of ultraviolet-related DNA damage and a profound platinum-related mutational signature in a chemotherapy-exposed tumour. Most RB1 mutations are identifiable by clinical screening. However, the increased resolution and ability to detect otherwise elusive rearrangements by WGS have important repercussions on clinical management and advice on recurrence risks.

Genetic predisposition in pediatric oncology

Identifying patients with a genetic predisposition for developing malignant tumors has a significant impact on both the patient and family. Recognition of genetic predisposition, before diagnosing a malignant pathology, may lead to early diagnosis of a neoplasia. Recognition of a genetic predisposition syndrome after the diagnosis of neoplasia can result in a change of treatment plan, a specific follow-up of adverse treatment effects and, of course, a long-term follow-up focusing on the early detection of a second neoplasia.

Responsible for genetic syndromes that predispose individuals to malignant pathology are germline mutations. These mutations are present in all cells of conception, they can be inherited or can occur de novo.

Several mechanisms of inheritance are described: Mendelian autosomal dominant, Mendelian autosomal recessive, X-linked patterns, constitutional chromosomal abnormality and non-Mendelian inheritance.

In the following review we will present the most important genetic syndromes in pediatric oncology.

Incidence and Mortality of Second Primary Cancers in Danish Patients With Retinoblastoma, 1943-2013

IMPORTANCE

In heritable retinoblastoma, there is a significantly increased risk of second primary cancers (SPCs). Improved knowledge about the incidence and influence of heritability and treatment is important during therapy for patients with retinoblastoma.

OBJECTIVE

To assess the incidence of SPC in patients diagnosed with retinoblastoma in Denmark from 1943 to 2013 with a focus on heritability and the association of external radiotherapy with mortality.

DESIGN, SETTING, AND PARTICIPANTS

In this retrospective cohort study, data were extracted from the Danish Ocular Oncology Group Database containing complete data on all patients diagnosed with retinoblastoma , and obtained from the Danish Cancer Registry, which includes information on all patients with cancer from 1943 to December 31, 2013. Data analysis was conducted from December 1, 2017, to October 1, 2019. Data on 323 patients were included.

EXPOSURES

Heritability and retinoblastoma treatment.

MAIN OUTCOMES AND MEASURES

Standardized incidence rate, excess absolute risk, cumulative incidence of SPC, and mortality from SPC. Association of heritability and treatment with outcomes was estimated.

RESULTS

Of the 323 patients included in the analysis, 181 were men (56%), 133 had heritable retinoblastoma (41%), and 190 had nonheritable retinoblastoma (59%). The median age at diagnosis of SPC was 32.4 (interquartile range, 15.4-43.9) years in patients with heritable retinoblastoma and 38.6 (interquartile range, 20.5-49.4) years in those with nonheritable retinoblastoma. Twenty-five SPCs were identified in patients with heritable retinoblastoma vs 14 in patients with nonheritable retinoblastoma. Standardized incidence rate (SIR) of SPC in patients with heritable retinoblastoma was 11.39 (95% CI, 7.37-16.81) with an excess absolute risk of 70 cases per 10 000 person-years; the highest SIRs were for sarcoma (181.13; 95% CI, 98.94-303.92) and malignant melanoma (26.78; 95% CI, 9.78-58.30). The SIR for SPC in patients with nonheritable retinoblastoma was 1.52 (95% CI, 0.81-2.60). The cumulative incidence of SPCs at age 60 years was significantly higher in patients with heritable retinoblastoma (51%) compared with those with nonheritable retinoblastoma (13%) (P < .001) (hazard ratio, 5.0; 95% CI, 2.5-10.3). No significant differences were identified in overall risk of SPC in patients with heritable retinoblastoma treated with 3 different modalities: external radiotherapy, plaque (but no external) radiotherapy, and enucleation only, but an increased proportion of sarcomas was noted in the irradiated field. Mortality due to SPC was also higher in survivors of heritable retinoblastoma compared with those with nonheritable retinoblastoma (cumulative mortality, 34% vs 12% at age 60 years; P = .03).

CONCLUSIONS AND RELEVANCE

The findings of this study suggest that the incidence and mortality associated with SPC were significantly higher in patients with heritable retinoblastoma vs patients with nonheritable retinoblastoma. The largest increases in risk were noted for sarcoma and malignant melanoma. External radiotherapy did not appear to increase the risk. These findings are relevant when treating patients with retinoblastoma to manage the risk for SPC.

Prognostic Information for Known Genetic Carriers of RB1 Pathogenic Variants (Germline and Mosaic)

PURPOSE

To compare the number of tumors per eye for mosaic carriers of RB1 pathogenic variants with full germline variants and the conversion from unilateral to bilateral disease.

DESIGN

Retrospective cohort study comparing patients with retinoblastoma and different genetic subtypes: high penetrance (HP), low penetrance (LP), and mosaicism.

PARTICIPANTS

Data were analyzed between 1992 and 2018 at the Retinoblastoma Unit, Royal London Hospital, London, United Kingdom. All familial patients had a parent with a known pathogenic variant even if the parent did not manifest the disease.

MAIN OUTCOME MEASURES

Number of tumors per eye in children who developed retinoblastoma in that eye. Other outcomes included total number of tumors per patient, age at diagnosis, laterality at presentation and later, sex, and stage according to International Intraocular Retinoblastoma Classification.

RESULTS

A total of 111 patients were included: 64 full germline, familial patients (53 HP and 11 LP) and 47 mosaic patients. Twelve HP patients (23%) were unilateral, and 8 of 12 patients (67%) developed tumors in their previously unaffected eye. A total of 34 mosaic patients (72%) were unilateral, and only 2 (6%) developed tumors in their unaffected eye. Age at diagnosis was higher in mosaic patients (median, 22 months) than in HP patients (median 7) (P < 0.00002). The number of tumors per eye was fewer in patients with mosaic alleles (median, 1.0; range, 1-6) compared with patients with HP alleles (median, 3.0; range, 1-8) (P < 0.0003). All 3 children (4 eyes) with mosaicism and more than 2 tumors per eye had high levels of mosaicism.

CONCLUSIONS

Children with mosaic alleles have fewer tumors per eye compared with those with known high-penetrant pathogenic variants and are more likely to remain unilateral. The level of mosaicism has an impact on laterality and number of tumors.

Variability in retinoblastoma genome stability is driven by age and not heritability

Retinoblastoma (RB) is a childhood intraocular cancer initiated by biallelic inactivation of the RB tumor suppressor gene (RB1^-/- ). RB can be hereditary (germline RB1 pathogenic allele is present) or non-hereditary. Somatic copy number alterations (SCNAs) contribute to subsequent tumorigenesis. Previous studies of only enucleated RB eyes have reported associations between heritability status and the prevalence of SCNAs. Herein, we use an aqueous humor (AH) liquid biopsy to investigate RB genomic profiles in the context of germline RB1 status, age, and International Intraocular Retinoblastoma Classification (IIRC) clinical grouping for both enucleated and salvaged eyes. Between 2014 and 2019, AH was sampled from a total of 54 eyes of 50 patients. Germline RB1 status was determined from clinical blood testing, and cell-free DNA from AH was analyzed for SCNAs. Of the 50 patients, 23 (46.0%; 27 eyes) had hereditary RB, and 27 (54.0%, 27 eyes) had non-hereditary RB. Median age at diagnosis was comparable between hereditary (13 ± 10 months) and non-hereditary (13 ± 8 months) eyes (P = 0.818). There was no significant difference in the prevalence or number of SCNAs based on (1) hereditary status (P > 0.56) or (2) IIRC grouping (P > 0.47). There was, however, a significant correlation between patient age at diagnosis, and (1) number of total SCNAs (r[52] = 0.672, P < 0.00001) and (2) number of highly-recurrent RB SCNAs (r[52] = 0.616, P < 0.00001). This evidence does not support the theory that specific molecular or genomic subtypes exist between hereditary and non-hereditary RB; rather, the prevalence of genomic alterations in RB eyes is strongly related to patient age at diagnosis.

Impact of RB1 gene mutation type in retinoblastoma patients on clinical presentation and management outcome

OBJECTIVE/BACKGROUND

Retinoblastoma (RB), the most common intraocular malignancy in children, is caused by biallelic inactivation of the human retinoblastoma susceptibility gene (RB1). We are evaluating the impact of the type of RB1 gene mutation on clinical presentation and management outcome.

METHODS

A retrospective case series of 50 patients with RB. Main outcomes were clinical and pathologic features and types of RB1 gene mutations detected using quantitative multiplex polymerase chain reaction (PCR), allele-specific PCR, next-generation sequencing analysis, and Sanger sequencing.

RESULTS

Twenty (40%) patients had unilateral RB and 30 (60%) had bilateral RB. Overall, 36 (72%) patients had germline disease, 17 (47%) of whom inherited the disease. Of these 17 inherited cases, paternal origin of the RB1 mutation was seen in 15 (88%). The overall eye salvage rate was 74% (n = 49/66; 100% for Groups A + B + C, and 79% for Group D eyes). The most frequent type of mutation was a nonsense mutation generating a stop codon (15/36, 42%). Other mutations that result in a premature stop codon due to deletions or insertions with donor splice site or receptor splice site mutations were detected in 7/36 (19%), 10/36 (28%), and 2/26 (6%) patients, respectively. The remaining two (6%) patients had frameshift mutation. Patients with deletion, acceptor splice site, and frameshift mutations presented with more advanced ICRB (International Classification of Retinoblastoma) stage (75% diagnosed with Group D or E), even though there was no significant difference in eye salvage rate or tumor invasiveness between patients with different types of mutations.

CONCLUSION

Despite the heterogeneous nature of RB1 gene mutations, tumor stage remains the most important predictive factor for clinical presentation and outcome. Furthermore, acceptor splice site and frameshift mutations are associated with more advanced tumor stage at diagnosis.

Next-Generation Technologies and Strategies for the Management of Retinoblastoma

Retinoblastoma (RB) is an inherited retinal disorder (IRD) caused by the mutation in the RB1 gene or, rarely, by alterations in the MYCN gene. In recent years, new treatment advances have increased ocular and visual preservation in the developed world. The management of RB has improved significantly in recent decades, from the use of external beam radiation to recently, more localized treatments. Determining the underlying genetic cause of RB is critical for timely management decisions. The advent of next-generation sequencing technologies have assisted in understanding the molecular pathology of RB. Liquid biopsy of the aqueous humor has also had significant potential implications for tumor management. Currently, patients' genotypic information, along with RB phenotypic presentation, are considered carefully when making treatment decisions aimed at globe preservation. Advances in molecular testing that improve our understanding of the molecular pathology of RB, together with multiple directed treatment options, are critical for developing precision medicine strategies to treat this disease.

Frequency of low-level and high-level mosaicism in sporadic retinoblastoma: genotype-phenotype relationships

Somatic mutational mosaicism is a common feature of monogenic genetic disorders, particularly in diseases such as retinoblastoma, with high rates of de novo mutations. The detection and quantification of mosaicism is particularly relevant in these diseases, since it has important implications for genetic counseling, patient management, and probably also on disease onset and progression. In order to assess the rate of somatic mosaicism (high- and low-level mosaicism) in sporadic retinoblastoma patients, we analyzed a cohort of 153 patients with sporadic retinoblastoma using ultra deep next-generation sequencing. High-level mosaicism was detected in 14 out of 100 (14%) bilateral patients and in 11 out of 29 (38%) unilateral patients in whom conventional Sanger sequencing identified a pathogenic mutation in blood DNA. In addition, low-level mosaicism was detected in 3 out of 16 (19%) unilateral patients in whom conventional screening was negative in blood DNA. Our results also reveal that mosaicism was associated to delayed retinoblastoma onset particularly in unilateral patients. Finally we compared the level of mosaicism in different tissues to identify the best DNA source to identify mosaicism in retinoblastoma patients. In light of these results we recommended analyzing the mosaic status in all retinoblastoma patients using accurate techniques such as next-generation sequencing, even in those cases in which conventional Sanger sequencing identified a pathogenic mutation in blood DNA. Our results suggest that a significant proportion of those cases are truly mosaics that could have been overlooked. This information should be taking into consideration in the management and genetic counseling of retinoblastoma patients and families.

The RB1 Story: Characterization and Cloning of the First Tumor Suppressor Gene

The RB1 gene is the first described human tumor suppressor gene and plays an integral role in the development of retinoblastoma, a pediatric malignancy of the eye. Since its discovery, the stepwise characterization and cloning of RB1 have laid the foundation for numerous advances in the understanding of tumor suppressor genes, retinoblastoma tumorigenesis, and inheritance. Knowledge of RB1 led to a paradigm shift in the field of cancer genetics, including widespread acceptance of the concept of tumor suppressor genes, and has provided crucial diagnostic and prognostic information through genetic testing for patients affected by retinoblastoma. This article reviews the long history of RB1 gene research, characterization, and cloning, and also discusses recent advances in retinoblastoma genetics that have grown out of this foundational work.

Low-level parental mosaicism in an apparent de novo case of Peutz-Jeghers syndrome

We report the case of a female found to have mosaicism for mutation in the STK11 gene, with the mutant allele expressed in her gametes, evident by her affected offspring, and in her gastrointestinal tract demonstrated on an excised polyp analysed for diagnosis. Mosaicism for Peutz-Jeghers syndrome (PJS) has been reported in a small number of cases previously but a clinical presentation such as this has not previously been described. This finding of mosaicism was several years after initial investigations failed to identify the same STK11 mutation in this woman whose son was diagnosed with PJS at a young age. This case highlights the importance of considering mosaicism as an explanation for apparent de novo cases of PJS syndrome. It also has implications for genetic counselling, predictive testing and cancer screening.

Constitutional Mosaic Epimutations - a hidden cause of cancer?

Silencing of tumor suppressor genes by promoter hypermethylation is a key mechanism to facilitate cancer progression in many malignancies. While promoter hypermethylation can occur at later stages of the carcinogenesis process, constitutional methylation of key tumor suppressors may be an initiating event whereby cancer is started. Constitutional BRCA1 methylation due to cis-acting germline genetic variants is associated with a high risk of breast and ovarian cancer. However, this seems to be a rare event, restricted to a very limited number of families. In contrast, mosaic constitutional BRCA1 methylation is detected in 4-7% of newborn females without germline BRCA1 mutations. While the cause of such methylation is poorly understood, mosaic normal tissue BRCA1 methylation is associated with a 2-3 fold increased risk of high-grade serous ovarian cancer (HGSOC). As such, BRCA1 methylation may be the cause of a significant number of ovarian cancers. Given the molecular similarities between HGSOC and basal-like breast cancer, the findings with respect to HGSOC suggest that constitutional BRCA1 methylation could be a risk factor for basal-like breast cancer as well. Similar to BRCA1, some specific germline variants in MLH1 and MSH2 are associated with promoter methylation and a high risk of colorectal cancers in rare hereditary cases of the disease. However, as many as 15% of all colorectal cancers are of the microsatellite instability (MSI) "high" subtype, in which commonly the tumors harbor MLH1 hypermethylation. Constitutional mosaic methylation of MLH1 in normal tissues has been detected but not formally evaluated as a potential risk factor for incidental colorectal cancers. However, the findings with respect to BRCA1 in breast and ovarian cancer raises the question whether mosaic MLH1 methylation is a risk factor for MSI positive colorectal cancer as well. As for MGMT, a promoter variant is associated with elevated methylation across a panel of solid cancers, and MGMT promoter methylation may contribute to an elevated cancer risk in several of these malignancies. We hypothesize that constitutional mosaic promoter methylation of crucial tumor suppressors may trigger certain types of cancer, similar to germline mutations inactivating the same particular genes. Such constitutional methylation events may be a spark to ignite cancer development, and if associated with a significant cancer risk, screening for such epigenetic alterations could be part of cancer prevention programs to reduce cancer mortality in the future.

Evidence of predisposing epimutation in retinoblastoma

Retinoblastoma (RB), which represents the most common childhood eye cancer, is caused by biallelic inactivation of RB1 gene. Promoter hypermethylation is quite frequent in RB tissues but conclusive evidence of soma-wide predisposing epimutations is currently scant. Here, 50 patients who tested negative for RB1 germline sequence alterations were screened for aberrant promoter methylation using methylation-specific MLPA. The assay, performed on blood, identified a sporadic patient with methylation of CpG106, absent in parents' DNA. Bisulfite pyrosequencing accurately quantified CpG methylation in blood DNA (mean ∼49%) and also confirmed the aberration in DNA isolated from oral mucosa although at lower levels (mean ∼34%). Using a tag-SNP, methylation was demonstrated to affect the maternal allele. Real-time qPCR demonstrated RB1 transcriptional silencing. In conclusion, we documented that promoter methylation can act as the first "hit" in Knudson's model. This mosaic epimutation mimics the effect of an inactivating mutation and phenocopies RB onset.

Retinoblastoma for Pediatric Ophthalmologists

Retinoblastoma can present in 1 or both eyes and is the most common intraocular malignancy in childhood. It is typically initiated by biallelic mutation of the RB1 tumor suppressor gene, leading to malignant transformation of primitive retinal cells. The most common presentation is leukocoria, followed by strabismus. Heritable retinoblastoma accounts for 45% of all cases, with 80% being bilateral. Treatment and prognosis of retinoblastoma is dictated by the disease stage at initial presentation. The 8th Edition American Joint Committee on Cancer (AJCC) TNMH (tumor, node, metastasis, heritable trait) staging system defines evidence-based clinical and pathological staging for overall prognosis for eye(s) and child. Multiple treatment options are available in 2018 for retinoblastoma management with a multidisciplinary team, including pediatric ocular oncology, medical oncology, radiation oncology, genetics, nursing, and social work. Survival exceeds 95% when disease is diagnosed early and treated in centers specializing in retinoblastoma. However, survival rates are less than 50% with extraocular tumor dissemination. We summarize the epidemiology, genetics, prenatal screening, diagnosis, classification, investigations, and current therapeutic options in the management of retinoblastoma.

Parent-of-origin effect of hypomorphic pathogenic variants and somatic mosaicism impact on phenotypic expression of retinoblastoma

Retinoblastoma is the most common eye cancer in children. Numerous families have been described displaying reduced penetrance and expressivity. An extensive molecular characterization of seven families led us to characterize the two main mechanisms impacting on phenotypic expression, as follows: (i) mosaicism of amorphic pathogenic variants; and (ii) parent-of-origin-effect of hypomorphic pathogenic variants. Somatic mosaicism for RB1 splicing variants (c.1960+5G>C and c.2106+2T>C), leading to a complete loss of function was demonstrated by high-depth NGS in two families. In both cases, the healthy carrier parent (one with retinoma) showed a variant frequency lower than that expected for a heterozygous individual, indicating a 56-60% mosaicism level. Previous evidences of a ~3-fold excess of RB1 maternal canonical transcript led us to hypothesize that this differential allelic expression could influence phenotypic outcome in families at risk for RB onset. Accordingly, in five families, we identified a higher tumor risk associated with paternally inherited hypomorphic pathogenic variants, namely a deletion resulting in the loss of 37 amino acids at the N-terminus (c.608-16_608del), an exonic substitution with a "leaky" splicing effect (c.1331A>G), a partially deleterious substitution (c.1981C>T) and a truncating C-terminal variant (c.2663+2T>C). The identification of these mechanisms changes the genetic/prenatal counseling and the clinical management of families, indicating a higher recurrence risk when the hypomorphic pathogenic variant is inherited from the father, and suggesting the need for second tumor surveillance in unaffected carriers at risk of developing adult-onset cancer such as osteosarcoma or leiomyosarcoma.

Robust identification of mosaic variants in congenital heart disease

Mosaicism due to somatic mutations can cause multiple diseases including cancer, developmental and overgrowth syndromes, neurodevelopmental disorders, autoinflammatory diseases, and atrial fibrillation. With the increased use of next generation sequencing technology, multiple tools have been developed to identify low-frequency variants, specifically from matched tumor-normal tissues in cancer studies. To investigate whether mosaic variants are implicated in congenital heart disease (CHD), we developed a pipeline using the cancer somatic variant caller MuTect to identify mosaic variants in whole-exome sequencing (WES) data from a cohort of parent/affected child trios (n = 715) and a cohort of healthy individuals (n = 416). This is a novel application of the somatic variant caller designed for cancer to WES trio data. We identified two cases with mosaic KMT2D mutations that are likely pathogenic for CHD, but conclude that, overall, mosaicism detectable in peripheral blood or saliva does not account for a significant portion of CHD etiology.

Knowledge, experiences and attitudes concerning genetics among retinoblastoma survivors and parents

Clinical genetic services are increasingly providing a more nuanced understanding of genetic disease diagnostics and future risk for patients. Effectively conveying genetic information is essential for patients to make informed decisions. This is especially important for survivors of heritable cancers such as retinoblastoma (childhood eye cancer), where survivors who carry a germline mutation in the RB1 gene are at increased risk of second cancers in adulthood, and of passing on the disease risk to future offspring. We conducted focus groups with adult survivors of retinoblastoma and parents of children with retinoblastoma, to uncover their knowledge of, experiences with and attitudes about retinoblastoma genetics and related impacts of the cancer. Results revealed that participants understood that retinoblastoma was a genetic disease, but often misunderstood the implications of genetics on cancer phenotype and risk. Experiences with genetic testing and counseling were generally positive, however, participants reported challenges in accessing genetic information and psychosocial support. Participants suggested more educational resources, peer-to-peer counseling, and psychosocial support would enhance uptake of important genetic information. The results of the study will inform patient-oriented approaches to deliver comprehensive genetic healthcare.

Incidental neuroblastoma with bilateral retinoblastoma: what are the chances?

A child with bilateral familial retinoblastoma underwent staging MRI brain and orbit which identified subtle leptomeningeal enhancement, thus prompting an MRI whole body, which revealed a retroperitoneal mass, confirmed on laparoscopic biopsy to be neuroblastoma. This is the first reported case of these two rare embryonal non-central nervous system tumors occurring concurrently. The cause of this concurrence is unknown despite their pathogenic similarities with a chance of 4 cases per 10 billion children aged 1-4 years. Incidental neuroblastomas in infants can regress spontaneously but this child underwent systemic chemotherapy for his retinoblastoma that may have caused regression of the neuroblastoma.

Patient understanding of genetic information influences reproductive decision making in retinoblastoma

BACKGROUND

Retinoblastoma is the most common malignant tumour of the eye in childhood, with nearly all bilateral tumours and around 17% to 18% of unilateral tumours due to an oncogenic mutation in the RB1 gene in the germline. Genetic testing enables accurate risk assessment and optimal clinical management for the affected individual, siblings, and future offspring.

MATERIAL AND METHODS

We carried out the first UK-wide audit of understanding of genetic testing in individuals with retinoblastoma. A total of 292 individuals aged 16 to 45 years were included.

RESULTS

Patients with bilateral disease were significantly more likely to understand the implications of retinoblastoma for siblings and children. There was a significant association between not knowing the results of genetic testing or not understanding the implications and not having children, particularly in women. Surprisingly, this was also true for individuals treated for unilateral disease with a low risk of retinoblastoma for their offspring.

CONCLUSION

We are concerned that individuals may be making life choices based on insufficient information regarding risks of retinoblastoma and reproductive options. We suggest that improvement in transition care is needed to enable individuals to make informed reproductive decisions and to ensure optimal care for children born at risk of retinoblastoma.

Mutation spectrum of RB1 mutations in retinoblastoma cases from Singapore with implications for genetic management and counselling

Retinoblastoma (RB) is a rare childhood malignant disorder caused by the biallelic inactivation of RB1 gene. Early diagnosis and identification of carriers of heritable RB1 mutations can improve disease outcome and management. In this study, mutational analysis was conducted on fifty-nine matched tumor and peripheral blood samples from 18 bilateral and 41 unilateral unrelated RB cases by a combinatorial approach of Multiplex Ligation-dependent Probe Amplification (MLPA) assay, deletion screening, direct sequencing, copy number gene dosage analysis and methylation assays. Screening of both blood and tumor samples yielded a mutation detection rate of 94.9% (56/59) while only 42.4% (25/59) of mutations were detected if blood samples alone were analyzed. Biallelic mutations were observed in 43/59 (72.9%) of tumors screened. There were 3 cases (5.1%) in which no mutations could be detected and germline mutations were detected in 19.5% (8/41) of unilateral cases. A total of 61 point mutations were identified, of which 10 were novel. There was a high incidence of previously reported recurrent mutations, occurring at 38.98% (23/59) of all cases. Of interest were three cases of mosaic RB1 mutations detected in the blood from patients with unilateral retinoblastoma. Additionally, two germline mutations previously reported to be associated with low-penetrance phenotypes: missense-c.1981C>T and splice variant-c.607+1G>T, were observed in a bilateral and a unilateral proband, respectively. These findings have implications for genetic counselling and risk prediction for the affected families. This is the first published report on the spectrum of mutations in RB patients from Singapore and shows that further improved mutation screening strategies are required in order to provide a definitive molecular diagnosis for every case of RB. Our findings also underscore the importance of genetic testing in supporting individualized disease management plans for patients and asymptomatic family members carrying low-penetrance, germline mosaicism or heritable unilateral mutational phenotypes.

Genetic screening in Iranian patients with retinoblastoma

PurposeThe most common intraocular tumor in childhood, retinoblastoma, is largely associated with mutations in the RB1 gene. In the most comprehensive RB1 screening in Iran, we evaluated the RB1 mutations in 106 patients with retinoblastoma, including 73 bilateral (heritable) and 33 unilateral (sporadic) cases.Patients and methodsMutations were identified using amplification refractory mutation system (ARMS) PCR and direct sequencing of the 27 coding exons of RB1 and multiplex ligation-dependent probe amplification (MLPA).Results and ConclusionWe found 33 (31%) and 64 (60%) patients with sporadic unilateral and bilateral retinoblastoma, respectively as well as 9 (8.5%) cases with hereditary bilateral retinoblastoma. In total, we identified 52 causative RB1 mutations in 106 patients (global mutation rate of 49%). Of the 52 patients, 48 (92%) had sporadic and familial bilateral and 4 (8%) had sporadic unilateral RB. Therefore, the detection rate of RB1 mutations was 66% (48/73) and 12% (4/33) in bilateral and unilateral cases, respectively. Mutations were classified as nonsense in 31 (60%), missense in 1 (2%), large deletion in 11 (21%), small deletion in the 7 novel (15%) and splice site mutation in 2 (4%) patients with RB. Of 31 nonsense mutations, 23 (74%) occurred in the 11 Arginine codons of the RB1. Seven mutations (13%) were novel, and 45 (87%) had been previously reported. Thirty-three mutations were single-base substitutions leading to 31 nonsense amino acid changes and 2 splice site mutations in introns 12 and 16 of RB1. The altered 3D model structures of the RB1 novel mutant proteins are also predicted in this study.

Genetics and Molecular Diagnostics in Retinoblastoma--An Update

Retinoblastoma is the prototype genetic cancer: in one or both eyes of young children, most retinoblastomas are initiated by biallelic mutation of the retinoblastoma tumor suppressor gene, RB1, in a developing retinal cell. All those with bilateral retinoblastoma have heritable cancer, although 95% have not inherited the RB1 mutation. Non-heritable retinoblastoma is always unilateral, with 98% caused by loss of both RB1 alleles from the tumor, whereas 2% have normal RB1 in tumors initiated by amplification of the MYCN oncogene. Good understanding of retinoblastoma genetics supports optimal care for retinoblastoma children and their families. Retinoblastoma is the first cancer to officially acknowledge the seminal role of genetics in cancer, by incorporating "H" into the eighth edition of cancer staging (2017): those who carry the RB1 cancer-predisposing gene are H1; those proven to not carry the familial RB1 mutation are H0; and those at unknown risk are HX. We suggest H0* be used for those with residual <1% risk to carry a RB1 mutation due to undetectable mosaicism. Loss of RB1 from a susceptible developing retinal cell initiates the benign precursor, retinoma. Progressive genomic changes result in retinoblastoma, and cancer progression ensues with increasing genomic disarray. Looking forward, novel therapies are anticipated from studies of retinoblastoma and metastatic tumor cells and the second primary cancers that the carriers of RB1 mutations are at high risk to develop. Here, we summarize the concepts of retinoblastoma genetics for ophthalmologists in a question/answer format to assist in the care of patients and their families.

Mosaicism and prenatal diagnosis options: insights from retinoblastoma

In sporadic cases, a post-zygotic mutational event signifies a somatic mosaicism in the affected child only, which implies that these mutations affect only a portion of the body. Therefore siblings do not need follow-up. On the other hand, a pre-zygotic mutation transmitted by an unaffected mosaic parent implies recurrent risks in offspring. To better estimate the contribution of pre- and post-zygotic events, we analysed 124 consecutive bilateral retinoblastoma probands, carrying a heterozygous RB1 pathogenic variant and their unaffected, non-carrier parents. In order to evaluate somatic mosaicism in blood, the deleterious RB1 pathogenic variant identified in the proband, was searched for in the unaffected parents, using targeted deep sequencing. Observed recurrences, which represent an estimation of germline and somatic mosaicisms, were recorded and computed in the sibships. Deep sequencing revealed one mosaic-unaffected parent out of 124 tested couples, which provides an estimation of the maximal risk of recurrence, due to parental mosaicism, at 0.4%. Follow-up in the sibships showed one recurrence, providing a maximal recurrence risk, due to parental mosaicism, at 0.8%. Two different statistical strategies led to close estimates (0.4 and 0.8% risks) which appeared 266-533-fold higher, as compared with the general population. These recurrence estimates could be considered when counselling couples with retinoblastoma or diseases with a high de novo mutation rate.

Retinoblastoma genetics in India: From research to implementation

Retinoblastoma is the prototypic genetic cancer. India carries the biggest burden of retinoblastoma globally, with an estimated 1500 new cases annually. Recent advances in retinoblastoma genetics are reviewed, focusing specifically on information with clinical significance to patients. The Indian literature on retinoblastoma clinical genetics is also highlighted, with a comment on challenges and future directions. The review concludes with recommendations to help clinicians implement and translate retinoblastoma genetics to their practice.

Prenatal versus Postnatal Screening for Familial Retinoblastoma

PURPOSE

To compare overall outcomes of conventional postnatal screening of familial retinoblastoma and prenatal RB1 mutation identification followed by planned early-term delivery.

DESIGN

Retrospective, observational study.

PARTICIPANTS

Twenty children with familial retinoblastoma born between 1996 and 2014 and examined within 1 week of birth.

METHODS

Cohort 1 included spontaneously delivered neonates examined within 1 week of birth and confirmed postnatal to carry their family's RB1 mutant allele. Cohort 2 included infants identified by amniocentesis to carry their family's RB1 mutant allele, and therefore scheduled for early-term delivery (36-38 weeks' gestation). Treatment for retinoblastoma was performed at the Hospital for Sick Children, Toronto, Canada.

MAIN OUTCOME MEASURES

Age at first tumor in each eye, eye stage, treatments given, ocular salvage, treatment success (defined as avoidance of enucleation, external-beam irradiation, or both), visual outcome, number of anesthetics, pregnancy or delivery complications, and estimated treatment burden.

RESULTS

Vision-threatening tumors were present at birth in 4 of 8 infants in cohort 1 and in 3 of 12 infants in cohort 2. Eventually, all infants demonstrated tumors in both eyes. At the first treatment, 1 of 8 infants in cohort 1 had eyes in stage cT1a/cT1a or cT1a/cT0 (smallest and least vision-threatening tumors), compared with 8 of 12 infants in cohort 2 (P = 0.02). Null RB1 germline alleles induced earlier tumors than low-penetrance alleles (P = 0.03). Treatment success was achieved in 3 of 8 children in cohort 1 compared with 11 of 12 children in cohort 2 (P = 0.002). Acceptable vision (better than 0.2 decimal) was achieved for 8 of 16 eyes in cohort 1 compared with 21 of 24 eyes in cohort 2 (P = 0.014). Useful vision (better than 0.1, legal blindness) was achieved for 8 of 9 children in cohort 1 compared with 12 of 12 children in cohort 2. There were no complications related to early-term delivery. Median follow-up was 5.6 years, cohort 1 and 5.8 years, cohort 2.

CONCLUSIONS

When a parent had retinoblastoma, prenatal molecular diagnosis with early-term delivery increased the likelihood of infants born with no detectable tumors, better vision outcomes, and less invasive therapy. Prenatal molecular diagnosis facilitates anticipatory planning for both the child and family.

Genetics of Retinoblastoma

Retinoblastoma is a malignant retinal tumor that affects young children. Mutations in the RB1 gene cause retinoblastoma. Mutations in both RB1 alleles within the precursor retinal cell are essential, with one mutation that may be germline or somatic and the second one that is always somatic. Identification of the RB1 germline status of a patient allows differentiation between sporadic and heritable retinoblastoma variants. Application of this knowledge is crucial for assessing short-term (risk of additional tumors in the same eye and other eye) and long-term (risk of nonocular malignant tumors) prognosis and offering cost-effective surveillance strategies. Genetic testing and genetic counseling are therefore essential components of care for all children diagnosed with retinoblastoma. The American Joint Committee on Cancer has acknowledged the importance of detecting this heritable trait and has introduced the letter "H" to denote a heritable trait of all cancers, starting with retinoblastoma (in publication). In this article, we discuss the clinically relevant aspects of genetic testing and genetic counseling for a child with retinoblastoma.

Genetic screening in patients with Retinoblastoma in Israel

Retinoblastoma (Rb) is a childhood tumor (~1 in 20,000 live births) developing in the retina due to mutations in the RB1 gene. Identification of the oncogenic mutations in the RB1 gene is important for the clinical management and for genetic counseling to families with a child or a parent affected with the tumor. Here we present our experience in detecting the pathogenic mutations in blood samples, from 150 unrelated Rb patients and highlight the relevant counseling issues. Mutation screening in the RB1 gene was based on Sanger sequencing, mosaicism of recurrent CpG transition mutations was detected by allele specific PCR and multiplex ligation dependent probe amplification for detecting of large deletions/duplications. The overall detection rate of mutations in our cohort was 55% (82/150). In the familial cases it was 100% (17/17), in bilateral and unilateral-multifocal sporadic cases 91% (50/55), and in the unilateral sporadic cases 19% (15/78). Nonsense mutations and small deletions or insertions that results in transcripts with premature termination codons that are subject to nonsense mediated decay were the most frequent, detected in 50/82 (61%) of the patients. The rest were large deletions detected in 14/82 (17%), splice site mutations detected in 11/82 (13%), missense mutations in four patients and mutations in the promoter sequence in three patients. Mutation mosaicism ranging from 10 to 30% was detected by allele specific PCR in ten patients, 9% (5/55) of patients with bilateral tumor and 33% (5/15) of the patients with unilateral tumor. In three patients rare variants were detected as the only finding which was also detected in other healthy family members. Allele specific amplification of recurrent mutations raises in our cohort the identification rate from 82 to 91% in the sporadic bilateral cases and from 13 to 19% in the unilateral sporadic cases. Most mosaic cases could not be identified by Sanger sequencing and therefore screening for recurrent CpG transition mutations by allele specific amplification is of utmost importance. Molecular screening is important for the genetic counseling regarding the risk for tumor development and the relevance for prenatal diagnosis but in several families is accompanied by detecting rare variants that might be rare polymorphisms or low penetrant mutations.