Population-based whole-genome sequencing with constrained gene analysis identifies predisposing germline variants in children with central nervous system tumors
Authors: Stoltze Ulrik Kristoffer , Foss-Skiftesvik Jon , van Overeem Hansen Thomas , Byrjalsen Anna , Sehested Astrid , Scheie David , Mikkelsen Torben Stamm , Rasmussen Simon , Bak Mads , Okkels Henrik , Callesen Michael Thude , Skjøth-Rasmussen Jane , Gerdes Anne-Marie , Schmiegelow Kjeld , Mathiasen René , Wadt Karin 
Published: March 2022

Background

The underlying cause of central nervous system (CNS) tumors in children is largely unknown. In this nationwide, prospective population-based study we investigate rare germline variants across known and putative CPS genes and genes exhibiting evolutionary intolerance of inactivating alterations in children with CNS tumors.

Methods

One hundred and twenty-eight children with CNS tumors underwent whole-genome sequencing of germline DNA. Single nucleotide and structural variants in 315 cancer related genes and 2,986 highly evolutionarily constrained genes were assessed. A systematic pedigree analysis covering 3,543 close relatives was performed.

Results

Thirteen patients harbored rare pathogenic variants in nine known CPS genes. The likelihood of carrying pathogenic variants in CPS genes was higher for patients with medulloblastoma than children with other tumors (OR 5.9, CI 1.6-21.2). Metasynchronous CNS tumors were observed exclusively in children harboring pathogenic CPS gene variants (n=2, p=0.01).

In general, known pCPS genes were shown to be significantly more constrained than both genes associated with risk of adult-onset malignancies (p=5e−4) and all other genes (p=5e−17). Forty-seven patients carried 66 loss-of-functions variants in 60 constrained genes, including eight variants in six known pCPS genes. A deletion in the extremely constrained EHMT1 gene, formerly somatically linked with sonic hedgehog medulloblastoma, was found in a patient with this tumor.

Conclusions

∽10% of pediatric CNS tumors can be attributed to rare variants in known CPS genes. Analysis of evolutionarily constrained genes may increase our understanding of pediatric cancer susceptibility.

3 key points

∽10% of children with CNS tumors carry a pathogenic variant in a known cancer predisposition gene

Known pediatric-onset cancer predisposition genes show high evolutionary constraint

Loss-of-function variants in evolutionarily constrained genes may explain additional risk

Importance of this study

Although CNS tumors constitute the most common form of solid neoplasms in childhood, our understanding of their underlying causes remains sparse. Predisposition studies often suffer from selection bias, lack of family and clinical data or from being limited to SNVs in established cancer predisposition genes. We report the findings of a prospective, population-based investigation of genetic predisposition to pediatric CNS tumors. Our findings illustrate that 10% of children with CNS tumors harbor a damaging alteration in a known cancer gene, of which the majority (9/13) are loss-of-function alterations. Moreover, we illustrate how recently developed knowledge on evolutionarily loss-of-function intolerant genes may be used to investigate additional pediatric cancer risk and present EHMT1 as a putative novel predisposition gene for SHH medulloblastoma. Previously undescribed links between variants in known cancer predisposition genes and specific brain tumors are presented and the importance of assessing both SV and SNV is illustrated.