RB1 screening of retinoblastoma patients in Sri Lanka using targeted next generation sequencing (NGS) and gene ratio analysis copy enumeration PCR (GRACE-PCR)

BACKGROUND

Retinoblastoma (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.

METHODS

Targeted 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.

RESULTS

There 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.

CONCLUSIONS

The 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.

Cornea Verticillata in classical Fabry disease, first from Sri Lanka: a case report

BACKGROUND

Fabry disease is a rare inborn error of metabolism with profound clinical consequences if untreated. It is caused by the deficiency of α galactosidase A enzyme and is the only lysosomal storage disorder with an X linked inheritance. Confirmation requires genetic analysis of Galactosidase Alpha (GLA) Gene, which is often a challenge in resource-poor settings. Despite these technological limitations, specific clinical features in this condition can establish the diagnosis.

CASE PRESENTATION

We report on a 13-year old male who presented with an afebrile convulsion with a background history of chronic burning sensation of hands and feet and anhidrosis for 2 years duration with a similar history of episodic acroparesthesia in the other male sibling. The early clinical diagnosis was based on the history and detection of Cornea Verticillata on eye examination. Biochemical confirmation was established with detection of low α galactosidase A enzyme levels and a missense mutation of the Galactosidase Alpha (GLA) Gene (c.136C > T) established the genetic confirmation.

CONCLUSION

This is the first case of Fabry disease reported in Sri Lanka. Awareness of specific clinical features aided clinical diagnosis long before access to genetic confirmation was available.

Role of ethnicity and socioeconomic status (SES) in the presentation of retinoblastoma: findings from the UK

Background

The relationship between the ethnic background or socioeconomic status (SES) and late retinoblastoma (Rb) presentation in the UK is unclear. We aimed to investigate if such correlations exist in a cohort of non-familial Rb cases.

Methods

A cross-sectional study based at the two centres providing Rb care in the UK. Included were non-familial Rb cases that presented from January 2006 to December 2011. Epidemiological and clinical data were retrieved from medical charts, as well as patients’ postcodes used to obtain the Index of Multiple Deprivation (IMD) score. A postal questionnaire was sent to participants’ parents to collect further, person-level, information on languages spoken and household socioeconomic position. Statistical correlations to advanced Rb at presentation as well as to treatment by enucleation and need for adjuvant chemotherapy were investigated.

Results

The cohort included 189 cases, 98 (51.8%) of which were males. The median age at diagnosis was 16 months (IQR 8–34 months). Of the study patients, 153 (81%) presented with advanced Rb; 78 (41%) with group D and 75 (40%) with group E Rb. A total of 134 (72%) patients were treated with enucleation. South Asian ethnicity and being in the most deprived IMD quintile were associated with a higher likelihood of presentation with advanced disease, but these estimates did not reach statistical significance. Older age at presentation was associated with enucleation and bilateral disease with adjuvant chemotherapy.

Conclusions

In this national UK study of patients with non-familial Rb, there was no evidence of an association of ethnicity or SES and the risk of presenting with advanced disease. These findings may reflect equality in access of healthcare in the UK.