For most people, a diagnosis of cystic fibrosis means the certainty of a life ended too soon. But for Isabel Stenzel Byrnes and Anabel Stenzel, twin girls with the disease, what began as a family’s stubborn determination grew into a miracle.

The tragedy of CF has been touchingly recounted in such books as Frank Deford’s Alex: The Life of a Child, but The Power of Two is the first book to portray the symbiotic relationship of twins who share this life-threatening disease through adulthood. Isabel and Anabel tell of their lifelong struggle to pursue normal lives with cystic fibrosis while grappling with the realisation that they will die young. Their story reflects the physical and emotional challenges of a particularly aggressive form of CF and is an honest and gripping portrayal of the daily struggle associated with long-term hospitalisation, the impact of chronic illness on marriage and family, and the importance of a support network to continuing survival.

Born in 1972, seventeen years before scientists discovered the genetic mutation that causes CF, the Stenzel twins endured the daily regimen of chest percussion, frequent doctor visits, and lengthy hospitalisations. But in the face of innumerable setbacks, their deep-seated dependence on each other allowed them to survive long enough to reap the benefits of the miraculous lung transplants that marked a turning point in their lives: “We have an old life - one of growing up with chronic illness - and anew life - one of opportunities and gifts we have never imagined before.” In this memoir, they pay tribute to the people who shaped their experience. These two remarkable sisters have much to teach about the power of perseverance - and about the ultimate power of hope.