Spectrum of RB1 Germline Mutations and Clinical Features in Unrelated Chinese Patients With Retinoblastoma

Abstract

Retinoblastoma (Rb) is a primary intraocular malignant tumor that occurs primarily in children, and results from loss-of-function mutations in the RB transcriptional corepressor 1 (RB1) gene. Genetic testing forms the basis of genetic counseling for affected families, as well as for clinical management of this disease. The aim of this study was to identify germline RB1 mutations and correlate the identified mutations with the clinical features of Rb patients. Genomic DNA was isolated from peripheral blood of 180 unrelated Rb patients and their parents (118 unilaterally and 62 bilaterally affected probands). Mutations in the RB1 gene, including the promoter region and exons 1-27 with flanking intronic sequences, were identified by Sanger sequencing. The samples with negative sequencing results were further subjected to methylation-specific multiplex ligation-dependent probe amplification (MS-MLPA) to detect gross deletions or duplications. Sixty-three distinct mutations were identified in 75 of the 180 (41.7%) probands. Of the 75 patients carrying RB1 mutations, 56 developed bilateral Rb, while 19 developed unilateral Rb. The total detection rates for bilateral and unilateral Rb were 90.3% (56/62) and 16.1% (19/118), respectively. Among the 75 patients, the spectrum of mutation types comprised 29.3% (22/75) nonsense mutations, 22.7% (17/75) splicing mutations, 17.3% (13/75) small insertions/deletions, 16.0% (12/75) large deletions/duplications, and 13.3% (10/75) missense mutations, while only 1% (1/75) of the mutations were in the promoter region of the RB1 gene. Age at diagnosis was significantly different (p < 0.01) between patients with positive and negative test results for germline RB1 mutations. A c.2359C > T mutation (p.R787X) was identified in identical twins, but one child was affected bilaterally and the other unilaterally. Of the five patients with deletion of the entire RB1 gene, the deletion of two patients was inherited from unaffected parents. In conclusion, in this study, we provide a comprehensive spectrum of RB1 germline mutations in Chinese Rb patients, and describe the correlations among RB1 mutations, age at diagnosis, and laterality; moreover, we report that the clinical features of individuals carrying an identical mutation in

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

“…Mean age at diagnosis for patients with bilateral Rb was lower than for unilateral cases (11 ± 7 months versus 20 ± 14, p < 0.0001 ). This finding is consistent with those of previous studies [ 3 , 12 , 13 ]. Leukocoria was the most common initial symptom in Rb cases, accounting for 65.8% of all cases, followed by squint (21.9%).…”

“…In this study, nonsense and frameshift mutations were the major mechanisms of RB1 inactivation, accounting for 73.3% of all RB1 mutations. This finding is consistent with previously reported rates of 50–80.32% [ 4 , 12 , 17 – 19 ]. Furthermore, 50.0% of all RB1 mutations lie in the A/B “pocket” domain of pRB, which can bind E2F transcription factors and promote protein–protein interactions [ 20 ].…”

“…Furthermore, 50.0% of all RB1 mutations lie in the A/B “pocket” domain of pRB, which can bind E2F transcription factors and promote protein–protein interactions [ 20 ]. This mutation rate was comparable to previously reported rates of 40–78.95% [ 4 , 12 , 17 , 21 , 22 ]. In addition, subtle mutations may result in partial inactivation of pRB, decreasing protein stability.…”

Genetics of congenital solid tumors

“…The molecular changes involved in pathogenesis are complex. The most common are germline or somatic mutations in the RB1 gene located on the chromosome 13q14.1-q14.2, this being the first tumor suppressor gene identified and expressed in various tissues [ 52 ]. It encodes the pRB protein which has multiple roles, the most important being the cell cycle stopping in the G1 phase, but also intervenes in cell differentiation, apoptosis control, chromosomal stability by temporarily stopping the cell cycle.…”

Expression of Ki67 as detected by MIB-1 and its association with histopathological high-risk factors among patients with retinoblastoma tumour: a cross-sectional study

“… 2 The mutations are 40% germline in nature and the other 60% of the mutations are sporadic. 3 The annual incidence of RbT for children with age ranging from 0 to 4 years in high-income countries (HICs) is 10.0–11.8 per 1 000 000 person-years. 4 The incidence reported in the literature for Africa particularly in the sub-Saharan African region is 9000 new cases per year, which corresponds to the incidence of 1 in 15 000 births.…”