Genetic and Epigenetic Profile of Retinoblastoma in a Chinese Population: Analysis of 47 Patients

Five novel RB1 gene mutations and genotype-phenotype correlations in Chinese children with retinoblastoma

Purpose

To identify the spectrum of RB1 gene mutations in 114 Chinese patients with retinoblastoma.

Methods

Genomic DNA was extracted from the peripheral blood of 114 Rb patients. Polymerase chain reactions (PCRs) followed by direct Sanger sequencing were used to screen for mutations in the RB1 gene, which contains 26 exons with flanking intronic sequences, except exon 15. Clinical data, including gender, age at diagnosis, laterality of ocular lesions, and associated symptoms, were recorded and compared.

Results

We identified five novel mutations in the RB1 gene. Twenty-five other mutations found in this study have been previously reported. A higher rate of RB1 mutations, with 47.3% of mutations among bilaterally affected patients vs. 6.8% within unilaterally affected patients, was also observed (p < 0.0001). Bilaterally affected patients were diagnosed earlier when compared to unilaterally affected patients (11 ± 7 months versus 20 ± 14 months, p = 0.0002). Furthermore, nonsense mutations were abundant (n = 14), followed by frameshift mutations (n = 8), splicing site mutations (n = 5), while missense mutations were few (n = 3).

Conclusions

We found five novel mutations in RB1 genes, which expands the mutational spectrum of the gene. Children with bilateral Rb exhibited higher mutation rates and were diagnosed earlier than those with unilateral Rb. These findings will inform clinical diagnosis and genetic therapeutic targeting in Rb patients.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10792-022-02341-2.

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.