High-sensitivity sequencing reveals multi-organ somatic mosaicism causing DICER1 syndrome

Area of Science:

• Genetics
• Oncology
• Molecular Biology

Background:

• Somatic mosaicism is increasingly recognized as a cause of non-Mendelian hereditary syndromes.
• Previous studies identified mosaic DICER1 mutations in some patients, but low-frequency mutations are hard to detect.
• Conventional mutation detection techniques failed to identify germline DICER1 mutations in four children with multiple tumors associated with DICER1 syndrome.

Purpose of the Study:

• To investigate the role of mosaic DICER1 mutations in children with multiple tumors and severe phenotypes.
• To evaluate sensitive methods for detecting low-frequency mosaic mutations.
• To identify additional genetic alterations in tumors associated with DICER1 syndrome.

Main Methods:

• Deep sequencing of DICER1 in constitutional DNA and tumor samples from four patients.
• Utilized three targeted-capture technologies, including HaloPlex(HS) with molecular barcodes.
• Analyzed for second somatic mutations and loss of heterozygosity (LOH) in tumors.

Main Results:

• Identical missense mutations in the DICER1 RNase IIIb domain were found in tumors from three patients, confirming mosaic origin.
• Mosaic mutations were detected in 0.24-31% of sequencing reads in constitutional DNA.
• Likely pathogenic second somatic mutations or LOH were discovered in tumors from all four patients.

Conclusions:

• Mosaic DICER1 mutations are a significant cause of severe DICER1 syndrome phenotypes.
• These mutations are often accompanied by second somatic mutations or LOH in associated tumors.
• HaloPlex(HS) technology offers the sensitivity needed to detect low-level mosaic mutations, with potential for broad application.