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

ABSTRACT

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.

KEYWORDS:

• Retinoblastoma
• RB1 pathogenic allele
• Mosaicism
• Next-generation sequencing
• Tissue distribution

Acknowledgments

Our most sincere thanks go to Professor Brenda L. Gallie of the Hospital for Sick Children, for her insightful suggestions regarding mosaic RB1 pathogenic alleles, critical review of the manuscript and encouragement to pursue retinoblastoma research. We would like to thank the mosaic research participants and their families for their generous tissue sample donations. Next-generation sequencing was performed in the laboratory of Geneseeq Technology Inc. We acknowledge grant funding support from the Open Research Project of Key Laboratory of Capital Medical University.

Disclosure statement

The authors report no conflicts of interest. The authors alone are responsible for the content and writing of this article.

Additional information

Funding

This study was supported by the Open Research Project of Key Laboratory of Capital Medical University (2016YNZL02).