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Alterations in the RB1 gene in Pakistani patients with retinoblastoma using direct sequencing analysis.

ABSTRACT: Retinoblastoma (RB) is a rare intraocular malignant tumor of the developing retina with an estimated incidence of 1:20,000 live births in children under the age of 5 years. In addition to the abnormal whitish appearance of the pupil or leukocoria, strabismus has also been reported as a clinical symptom of the disease. RB1 is the first cloned tumor suppressor gene, and mutational inactivation of this gene is responsible for the development of RB during early childhood. The purpose of this study was to identify mutational alterations in the RB1 gene in Pakistani patients with RB.During this study, 70 clinically evaluated patients with RB were recruited from different regions of Pakistan. The cases included 23 sporadic bilateral (32.9%), 34 sporadic unilateral (48.6%), nine familial bilateral (12.8%), and four familial unilateral (5.7%) cases. Constitutional causative mutations in the RB1 gene were screened via direct sequencing of all RB1 exons and their flanking regions.In this report, genetic testing resulted in the identification of 18 mutations in 25 patients with RB including six novel RB1 mutations. Of the total mutations identified, 13 (72.22%) were found to be null mutations caused by nine nonsense, three deletions, and one insertion. Two (11.11%) missense, two (11.11%) splice site mutations, and one (5.55%) base substitution in the promoter region were also found. Moreover, ten intronic variants were identified, one of which is novel.Molecular screening and identification of these mutations in Pakistani patients with RB provide the mutational variants of the RB1 gene in the Pakistani population. The detection of oncogenic mutations in patients with RB and genetically predisposed individuals is a major step in clinical management, prognosis, follow-up care, accurate genetic counseling, and presymptomatic diagnosis of RB.

SUBMITTER: Kalsoom S

PROVIDER: S-EPMC4575903 | biostudies-literature | 2015

REPOSITORIES: biostudies-literature

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Alterations in the RB1 gene in Pakistani patients with retinoblastoma using direct sequencing analysis.

Kalsoom Saeeda S Wasim Muhammad M Afzal Sibtain S Shahzad Muhammad Saqib MS Ramzan Shaiqa S Awan Ali Raza AR Anjum Aftab Ahmed AA Ramzan Khushnooda K

Molecular vision 20150917

<h4>Purpose</h4>Retinoblastoma (RB) is a rare intraocular malignant tumor of the developing retina with an estimated incidence of 1:20,000 live births in children under the age of 5 years. In addition to the abnormal whitish appearance of the pupil or leukocoria, strabismus has also been reported as a clinical symptom of the disease. RB1 is the first cloned tumor suppressor gene, and mutational inactivation of this gene is responsible for the development of RB during early childhood. The purpose ...[more]

PMID: 26396485

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Project description:BackgroundRetinoblastoma (RB) a tumour affecting those under 5 years, has a prevalence of 1 in 20,000, with around twenty new diagnoses per year in Sri Lanka. Unilateral and bilateral RB presents around 24 and 15 months respectively. Approximately 10% are familial. Systematic genetic testing for germline pathogenic variants of RB1, the only gene associated with an inherited risk of RB, is unavailable in Sri Lanka. Genetic testing optimizes management of affected children and at-risk siblings. This study aimed to develop accessible genetic testing to identify children with a germline pathogenic variant of RB1 in Sri Lanka.MethodsTargeted next generation sequencing (NGS) for detecting pathogenic sequence variants and Gene Ratio Analysis Copy Enumeration PCR (GRACE-PCR) for detecting RB1 copy number variations (CNVs) were performed for 49 consecutive RB patients treated between 2016 and 2020 at the designated RB care unit, Lady Ridgway hospital, Colombo. Patients (bilateral RB (n = 18; 37%), unilateral n = 31) were recruited following ethical clearance and informed consent.ResultsThere were 26 (53%) females. Mean age at diagnosis was 18 months. Thirty-five patients (71%) had undergone enucleation. Germline pathogenic variants of RB1 identified in 22/49 (45%) patients including 18 (37%; 12 bilateral and 6 unilateral) detected by targeted NGS (2 missense, 7 stop gained, 1 splice donor, 8 frameshift variants). Six were previously undescribed, likely pathogenic frameshift variants. Four bilateral RB patients had GRACE-PCR detected CNVs including one whole RB1, two intragenic deletions (exon 12/13; exon 11 and 23) and a partial duplication of exon 27. The only familial case (affected mother and child) shared the duplication. Only 2 of 4 CNVs and 10 of 18 pathogenic variants were confirmed by whole exome sequencing and Sanger sequencing respectively, due to funding limitations.ConclusionsThe study identified pathogenic or likely pathogenic germline RB1 sequence variants and copy number variants in 16/18 (89%) bilateral and 6/31(19%) unilateral cases, which is comparable to worldwide data (10-15% unilateral, 80-85% bilateral). Targeted NGS combined with GRACE-PCR significantly reduce the cost of RB1 testing in Sri Lanka, and may widen access for genetic diagnosis of RB patients in other low and middle income countries.

Project description:PurposeTo determine the usefulness of a comprehensive, targeted-capture next-generation sequencing (NGS) assay for the clinical management of children undergoing enucleation for retinoblastoma.DesignCohort study.ParticipantsThirty-two children with retinoblastoma.MethodsWe performed targeted NGS using the UCSF500 Cancer Panel (University of California, San Francisco, San Francisco, CA) on formalin-fixed, paraffin-embedded tumor tissue along with constitutional DNA isolated from peripheral blood, buccal swab, or uninvolved optic nerve. Peripheral blood samples were also sent to a commercial laboratory for germline RB1 mutation testing.Main outcome measuresPresence or absence of germline RB1 mutation or deletion, tumor genetic profile, and association of genetic alterations with clinicopathologic features.ResultsGermline mutation or deletion of the RB1 gene was identified in all children with bilateral retinoblastoma (n = 12), and these NGS results were 100% concordant with commercial germline RB1 mutation analysis. In tumor tissue tested with NGS, biallelic inactivation of RB1 was identified in 28 tumors and focal MYCN amplification was identified in 4 tumors (2 with wild-type RB1 and 2 with biallelic RB1 inactivation). Additional likely pathogenic alterations beyond RB1 were identified in 13 tumors (41%), several of which have not been reported previously in retinoblastoma. These included focal amplifications of MDM4 and RAF1, as well as damaging mutations involving BCOR, ARID1A, MGA, FAT1, and ATRX. The presence of additional likely pathogenetic mutations beyond RB1 inactivation was associated with aggressive histopathologic features, including higher histologic grade and anaplasia, and also with both unilateral and sporadic disease.ConclusionsComprehensive NGS analysis reliably detects relevant mutations, amplifications, and chromosomal copy number changes in retinoblastoma. The presence of genetic alterations beyond RB1 inactivation correlates with aggressive histopathologic features.

Project description:Retinoblastoma (RB) is an inherited childhood ocular cancer caused by mutations in the tumor suppressor RB1 gene. Identification of RB1 mutations is essential to assess the risk of developing retinoblastoma in the patients´ relatives. Retinoblastoma is a potentially curable cancer and an early diagnosis is critical for survival and eye preservation. Unilateral retinoblastoma is mostly non-heritable and results from two somatic mutations whereas bilateral retinoblastoma is heritable and results from one germline and one somatic mutation, both have high penetrance, 90%. The purpose of this study was to identify causative RB1 mutations in RB patients with different clinical presentations. A comprehensive approach was used to study a cohort of 34 patients with unilateral, bilateral and trilateral retinoblastoma. Blood and tumor DNA was analyzed by sequencing and multiplex ligation-dependent probe amplification (MLPA) assay. Validation of an insertion mutation was performed by cloning the PCR product. Most of the patients in our cohort had unilateral RB, eight patients had bilateral RB and one patient had a trilateral tumor with ocular and suprasellar/sellar locations. Other tumors in addition to retinoblastoma were also found in the affected families. One patient had two syndromes, retinoblastoma and schwannomatosis, and another RB patient had a father with a retinoma. Five out of the 25 unilateral RB patients carried germinal mutations (20%), which were mostly missense mutations. The bilateral and trilateral patients carried splice-site, nonsense and frameshift mutations as well as a whole RB1 gene deletion. Missense mutations were associated with mild phenotype: unilateral retinoblastoma, retinoma or no tumor. In this study we identified causative RB1 mutations in most bilateral RB patients and in some unilateral RB patients, including five novel mutations. These data are crucial for genetic counseling and confirm the need to perform complete genetic screening for RB1 mutations in both constitutional and tumor tissues.

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Alterations in the RB1 gene in Pakistani patients with retinoblastoma using direct sequencing analysis.

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Alterations in the RB1 gene in Pakistani patients with retinoblastoma using direct sequencing analysis.

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