For most people, a diagnosis of cystic fibrosis means the certainty of a life ended too soon. But for 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 between twins who share this life-threatening disease through adulthood. Isabel Stenzel Byrnes and Anabel Stenzel tell of their lifelong struggle to pursue normal lives with cystic fibrosis while grappling with the realization that they will die young. Their story reflects the physical and emotional challenges of a particularly aggressive form of CF and tells how the twins' bicultural heritage - Japanese and German - influenced the way they coped with these challenges.

Born in 1972, 17 years before scientists discovered the genetic mutation that causes CF, Isabel and Anabel endured the daily regimen of chest percussion, frequent doctor visits, and lengthy hospitalizations. But they tell how, 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 crossroads in their lives: "We have an old life - one of growing up with chronic illness - and a new life - one of opportunities and gifts we have never imagined before." In this memoir, they pay tribute to the people who shaped their experience.

The Power of Two is an honest and gripping portrayal of day-to-day health care, the impact of chronic illness on marriage and family, and the importance of a support network to continuing survival. It conveys an important message to both popular and professional listeners as it addresses key psychosocial issues in chronic illness throughout the sufferer's lifespan and illuminates the human side of advances in biotechnology.

Even as gene therapy and stem-cell research increase the chances for eradicating CF, this stirring account portrays its effects on one family that refused to give up. These two remarkable sisters have much to teach about the power of perseverance - and about the ultimate power of hope.

The book is published by University of Missouri Press.