A quantitative measurement of the human somatic mutation rate

Area of Science:

• Somatic cell genetics
• Cancer biology
• Human genetics

Background:

• The mutation rate (mu) is crucial for understanding malignant transformation but difficult to measure in human cells.
• The X-linked PIG-A gene, essential for glycosylphosphatidylinositol-linked proteins, serves as a potential indicator for mutation rate.
• Previous work established accurate measurement of PIG-A mutant cell frequency (f) using flow cytometry.

Purpose of the Study:

• To establish a reliable method for measuring somatic mutation rates in human B-lymphoblastoid cell lines.
• To investigate mutation rates in individuals with specific genetic predisposition syndromes.
• To assess the utility of this method for cancer risk evaluation and prevention strategies.

Main Methods:

• Culturing B-lymphoblastoid cell lines and removing pre-existing PIG-A mutants via flow sorting.
• Quantifying new PIG-A mutant cell frequency using flow cytometry with antibodies against glycosylphosphatidylinositol-linked proteins (e.g., CD48, CD55, CD59).
• Calculating mutation rate (mu) using the formula mu = f/d, where d is the number of cell divisions.

Main Results:

• The mean mutation rate in normal donors was 10.6 x 10(-7) mutations per cell division.
• A >30-fold elevation in mutation rate was observed in Fanconi anemia cells (P < 0.0001).
• Ataxia-telangiectasia cells showed a 4-fold elevation in mutation rate (P = 0.002), while Nijmegen breakage syndrome cells did not differ significantly from normal.

Conclusions:

• Somatic mutation rates can now be routinely measured in human B-lymphoblastoid cell lines.
• Elevated mutation rates are linked to cancer predisposition syndromes like Fanconi anemia and ataxia-telangiectasia.
• This assay system offers a valuable tool for assessing cancer risk and informing preventive strategies.