Geneticist Susan Weiss Liebman discovers a deadly DNA mutation in her family members that has been causing unexplained abrupt deaths for generations. Her investigation, detailed in her new book The Dressmaker's Mirror, reveals that her niece Karen's death was caused by dilated cardiomyopathy (DCM), a genetic condition that weakens the heart. Dr. Liebman's research uncovers a potentially lethal gene mutation responsible for making a protein crucial for maintaining the function and structure of muscle cells, including those in the heart. The mutation is found to be a major cause of DCM among Ashkenazi Jews. Dr. Liebman alerts her family members about the gene mutation and finds that neither she nor her children carry it, meaning they cannot pass it on to future generations.