“Do not take for granted what you have today. Tomorrow is not guaranteed. We must always strive to do our best. There are times we can’t always see the light at the end of the tunnel, but it is there. We have to choose to make it worth it.”

Meb Keflezighi, top American marathoner, Olympic silver medalist and ING New York City Marathon winner

When doctors diagnosed my little sister with a fatal brain disease in July 2006, I vowed to do two things:

• Never take another day for granted
• Help save Taylor’s life

It’s been close to eight years since Batten disease crashed into our lives. In that time, I’ve lost my way more than once. Sometimes, I focus on the wrong things. I don’t always listen to my heart. I’ve let Batten disease steal pieces of my sister while I watch, helpless. Pieces we can never get back.

But I feel blessed that in that time, we’ve also shared moments that I’ll never forget. Taking a trip to Disney World months after her diagnosis and before dark curtains fell on her eyes, so rare and beautiful. Receiving private concerts on her stage, my parents’ fireplace, before Batten disease silenced her singing voice. Eating melting ice cream cones together on sticky summer evenings when she could still hold a cone – and a spoon. Racing through the wet sand and into the Atlantic Ocean to crash knees-first into the waves before the monster stole her ability to run and walk.

In that time, I’ve also been a small part of monumental advancements in the fight against not just Batten disease, but also the thousands of rare diseases that affect 350 million people around the world as well as common brain-based and genetic diseases, from Alzheimer’s disease and Parkinson’s disease to age-related macular degeneration, multiple sclerosis and even HIV/AIDS. The gene therapy being tested at the University of North Carolina for infantile and late infantile Batten disease – work co-funded by Taylor’s Tale – could, indirectly, help hundreds of millions of people.

My sister’s story will change the world.

On Dec. 31, I texted my mom and invited her, my dad and Taylor out for a low-key dinner at our favorite pizza place. She accepted right away. Afterward, we decided, we’d go our separate ways.

But John and I arrived at the restaurant a few minutes late. We walked in to the cacophony of noisemakers and screaming kids. In the back of the room, we found Taylor, shell-shocked, gasping for air, with my distraught parents. In a flash, we shuttled my sister out of the pizza place, into the car and to the quiet of my house. During the next several hours, as most of the East Coast celebrated the New Year, kissed loved ones, drank champagne and gave thanks for clean slates, we watched Taylor slip further from our grasp without ever leaving my sofa. I’ve watched Batten disease inflict unspeakable horrors, but I’d never witnessed anything quite like what Taylor endured on New Year’s Eve. When Mom and Dad took her home an hour before the clock struck midnight, I watched their tail lights wink in the distance, then disappear…and at that moment, I knew that my little sister had just gone down the rabbit hole.

Meb’s right; tomorrow isn’t guaranteed – for Taylor, for me or for you. We can’t live in constant fear, but we should recognize the gifts we have, no matter how great or small they may be. Our paths won’t always be lit; my family’s path has been cloaked in shadow more often than not. But if we believe, we’ll have more good moments than bad. If we believe, we’ll get to the end of our tunnel. And the light at the end is a beautiful, bright light, more magnificent than anything you or I have ever seen.