HOUSTON, Texas (KTRK) -- Four years ago, the Clark family was hit with a diagnosis that they never expected.
Two of their children were diagnosed with a rare, fatal genetic disorder that has no known cure.
It's that diagnosis that is pushing them to inspire others around the world, one bike, step or swim at a time.
The Clarks are like any other Houston family. Lagenia and Dave have three children, 16-year-old twins Justin and Jared and 12-year-old Lexi.
To look at them you'd never know that together they're facing the unimaginable fact that Justin and Lexi have an extremely rare genetic disorder known as giant axonal neuropathy, or GAN.
GAN affects the central nervous system. It is a recessively inheritied condition that results in progressive nerve death.
Patients with GAN will eventually become quadriplegic. The average life expectancy for someone with GAN is just into their early 20s.
"My husband and I both carry the deletion gene that leads to GAN. We have better odds of winning a multi-million dollar lottery than meeting, having children and passing on this rare recessive gene," said Lagenia.
But they did.
Justin first started showing symptoms of something but was given several incorrect diagnoses. Days before he was to undergo reconstructive surgery he was able to have genome sequencing and was correctly diagnosed with GAN.
One of the key characteristics of children with GAN is extremely tight, curly hair. Justin has that curly hair.
Lagenia and Dave realized their daughter Lexi had those same curls. Thanks to Justin's diagnosis, with a simple cheek swab they were able to determine that Lexi also had GAN.
"I was a complete disaster," said Lagenia after learning two of her children had GAN. "It's incredibly hard as a parent to watch your child growing up and knowing what's coming and not being able to stop it."
GAN is so rare, there are only 74 known patients living with GAN worldwide right now.
After the initial shock of the diagnosis wore off, the Clarks knew they were going to do whatever they could to keep their children healthy for as long as possible. That meant staying active.
Keeping their core strong can help keep Justin and Lexi on their feet and healthy for longer. The Clarks have literally hit the ground running, riding and swimming.
Triathlons have been a huge part of their lives. Justin can no longer compete, but Lexi still takes part in kids' triathlons and even competes in the swim portion of adult races.
Justin is still active as part of his school's swim team.
"I swim the 100M and 200M freestyle events and enjoy being on the St. Pius High School (swim) team with my friends," said Justin.
Justin is grateful that he's had a slower progression of the disease and that he's been able to stay active longer than many of the other GAN patients he knows.
It's something he doesn't take for granted.
"I try to be a voice for those who don't have one."
Lexi also has been able to stay active longer than most, in part, because she was diagnosed before she was having any symptoms.
She can no longer compete in triathlons but she's still running and riding and enjoys playing sports like volleyball and basketball.
Jared doesn't have GAN but says the bravery, determination and perseverance his siblings show in the face of their health struggles inspires him to push himself harder.
One way he pushes himself is by creating, and competing in, the Splash & Dash to raise money for Hannah's Hope Fund.
Sunday was the second year for the race and participants raised $8,945.
Hannah's Hope Fund raises money for treatments and the development of a cure for GAN.
Organizations like these have allowed Justin and Lexi to meet and connect with other children with GAN from around the world. They've met kids from Germany, New Zealand, Canada, India and beyond.
"We are able to ask questions and the families with older kids are able to help the families with younger kids. We are also there for each other when we lose a member of the GAN family," said Lagenia.
The reality of GAN is not something that is lost on the Clarks. They focus every day on making memories and spending as much one-on-one time with each of their children as they can. This includes taking special trips while Justin and Lexi are able to travel as well as they can.
When times get tough, they rely on their faith to get them through.
"We are facing this severe diagnosis and uncertain future, watching our children's response to this adversity has only strengthened our faith in God," said Lagenia.
Justin echoes that sentiment.
"I don't think of GAN as a bad thing. God has a purpose for everything, and through GAN, I have reached many lives and will continue to spread my faith that has only strengthened by this disease," said Justin.
Overall, Justin and Lexi just want to live each day like the kids they are and they try not to let GAN get in their way. They don't see themselves as inspirations.
"I sometimes do get scared by this but I'm not really like... I know it's life threatening but it doesn't scare me every day. It just scares me sometimes when I think about it," said Lexi.
Currently, Justin and Lexi are waiting to be admitted into a National Institutes of Health study that is looking for possible ways to replace the damaged gene and halt the progression of the disease.
They see physicians at the Blue Bird Clinic at Texas Children's Hospital and at NIH.
For more information about GAN, or how to support the Clark family, visit Justin's Triumph Over GAN and Hannah's Hope Fund.