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TSC is caused by a mutation in one of two known genes: TSC1 located on chromosome 9 and TSC2 located on chromosome 16. Both are believed to suppress tumor growth in the body. When either of the genes is defective, tumors are not suppressed and tuberous sclerosis results.
First identified in the 1880s by a French physician named Bourneville – and long known as
Bourneville's disease – TSC has a broad range of manifestations that can include involvement of the heart, brain, lungs, kidney, skin and eyes. Males and females are equally likely to have TSC, and the chance of passing on the disorder to offspring is 50 percent.
"The true prevalence of tuberous sclerosis is unknown, but its incidence was recently estimated to be one in 6,000 live births,"said Hope Northrup, MD, a medical geneticist on staff at Children's Memorial Hermann Hospital and professor and director of the division of medical genetics in the department of pediatrics at The University of Texas Medical School at Houston. "This means about 50,000 people in the United States and more than a million worldwide have tuberous sclerosis.”
While some TSC patients have no brain involvement at all, frequently there are brain findings, so the disease is diagnosed with brain MRI or CT. In those like Mackenzie, whose brain is affected by the disorder, the most common manifestation is seizures, which occur in 60 percent to 90 percent of people diagnosed with TSC.
Once Mackenzie's seizures started, they were on a roll. "She had myoclonic seizures, infantile spasms and absence. After a seizure, she'd be tired and sleep for 45 minutes, then wake up and have another seizure. Ultimately, she was having about 10 a day," Mudd said. "We went through a myriad of drugs, starting with phenobarbital, which was effective for about two months.
When she was 18 months old, we put her on Klonopin, then Tegratol. Finally, we stumbled on Zarontin, which gave her good control for a few years, but the drug tired her. She was always tired.”
Eventually, Zarontin ceased to be effective in controlling Mackenzie's seizures. In 2003, her doctors suggested an alternative that might help – vagus nerve stimulation using an implant that sends a continuous stream of electrical pulses to the brain to control seizures. With the implant and two medications, including an anticonvulsant, Mackenzie has been seizure-free for two-and-a-half years.
Today, she's a full-fledged teenager, bopping to music on her favorite CDs and fighting her sisters for computer time. In her 13 years of life, she has endured seven invasive surgeries, suffered more than 5,000 epileptic seizures and taken more than 11,000 doses of anticonvulsants.
"Mackenzie's story is a moderate tuberous sclerosis story," her mother said. "It's not the worst. It's not the best. She was my first child, and she was perfect for a full year. When we learned about her disease, I had to let go of what was and prepare for what would be. Suffering of all children is horrible, but you move forward, you do your best, you thank God for all you've got. I can't imagine life without her.”
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