At age 23, Sachiko Ishizuka discovered that her father was battling an incurable muscle disease that can run in families, a wave of dismay soon coming over her at the thought that she may have inherited it.

But then her mother, in a bid to appease her, told Ishizuka that she did not need to worry — the man diagnosed with the genetic disease was actually not her biological father. Even more staggering was the revelation that, more than 20 years ago, Ishizuka was born as a result of reproductive treatment using donor sperm at the prestigious Keio University Hospital. As to who the sperm donor was, her mother said she did not have the faintest idea.

“At first I was relieved that I at least hadn’t inherited the disease,” Ishizuka, now 41, recalled in a recent interview. But her mother’s confession “denied everything I believed about my biological origin, which made me feel as if the entire 23 years of my life had been built upon a falsehood. I felt like my identity was crumbling away.”