When my husband Dave and I learned that two of our three daughters had a fatal genetic disease, we entered the kind of nightmare for which no parent can fully prepare. Both girls — Keira and Livvy — were diagnosed with metachromatic leukodystrophy, or MLD, a rare degenerative disorder that destroys the nervous system and gradually robs children of the ability to walk, speak, swallow, and ultimately survive.

But Keira had something that Livvy did not: time.