Study uncovers source of genetic variation influencing childhood brain tumors microbiologystudy

Researchers still do not have a comprehensive picture of the factors that influence gene expression in human cancers. Understanding gene expression in cancer is important because it can reveal how the disease begins, develops and potentially how to control it or eliminate it.

Looking to improve our understanding in this field, researchers at Baylor College of Medicine and collaborating institutions investigated for the first time in cancer the association between two sources of genetic variation: germline or inherited structural variation (SV), which refers to large differences in the DNA sequence, and DNA methylation, which is when genes are turned on or off without altering the DNA code.

They found that germline SVs influence DNA methylation in various types of brain tumors, which altered the expression of numerous genes. The team created a catalog of the genes affected. Although many of these gene changes might not play a part in cancer, some seem to be involved in cancer-related roles, including predisposition to the disease and patient survival. The study is published in Nature Communications.

“Scientists have learned a great deal about how cancer emerges and develops by studying changes or mutations in individual ‘letters’ of the genetic code. We have taken a different approach by studying how larger variations in the genetic code, known as germline or inherited structural variation, influence gene expression in human cancers,” said corresponding author Dr. Chad Creighton, professor of medicine and co-director of cancer bioinformatics at the Dan L Duncan Comprehensive Cancer Center at Baylor.

“Structural variation refers to large differences in the DNA sequence across individuals involving missing, duplicated or switched-around DNA sections. These larger variations can affect how genes are turned on or off, especially when they occur near important control regions of the genome.”

DNA methylation is another way cells regulate normal genetic variation across individuals. In this case, cells regulate their gene activity without changing the genetic code. Known as epigenetics, the mechanism works by adding chemical tags such as methyl groups on DNA. The tags act like a switch that can turn a gene on or off. Previous studies have shown that both SVs and DNA methylation alterations are associated with cancer.

“We analyzed germline SVs and tumor DNA methylation in 1,292 samples from children with brain tumors as provided by the Children’s Brain Tumor Network (CBTN),” Creighton said. “We found that thousands of SVs were linked to differing levels of DNA methylation in the tumors. Some of the differences affected gene enhancers, which regulate the expression of other genes.

“In many cases, these genetic variants occur near genes known to be involved in cancer predisposition, such as MSH2, RSPA and PALB2. Other genes with SVs and methylation changes were associated with patient survival, including gene POLD4.”

The researchers hope their findings will guide future studies to better understand the landscape of genetic and epigenetic influences in cancer and eventually lead to improved tools for identifying children at risk or tailoring therapies to individual genetic profiles.