What’s CMT4B3? The Disease Behind Hunter’s Diagnosis
CMT4B3 is a rare, progressive genetic neuromuscular disease. This means that Hunter was born with CMT4B3. It’s a recessive disease, which means you need two mutated copies of the SBF1 gene to have it—one from each parent. Hunter inherited one mutated copy from me and one from my husband. (No, we’re not related—we both just happened to carry different mutations.)
The disease primarily affects the nerves, especially the long ones that run from the brain to the feet and hands. Over time, the axons (the middle part of the nerve) break down, causing the brain’s signals to struggle in reaching the muscles. This is why Hunter has mobility issues and weakness in his hands.
But it’s not just about muscle weakness. There’s also a complex cranial nerve phenotype involved, which—if you’re wondering—means the nerves in Hunter’s face aren’t working the way they should. These are the nerves that go to the eyes, ears, and mouth. For Hunter, this causes vision problems and speech issues (like tongue wasting, which makes speaking harder).
We got Hunter’s diagnosis on May 19th, 2020, during the lockdown via Zoom. Yes, Zoom. In the middle of a pandemic, on a call with a geneticist, our world shifted. Before this, every doctor we saw assured me that Hunter was “fine.” They said he was just a bright little boy who was a little delayed. So when the diagnosis came in, it was a huge shock—one of the biggest shocks of my life.
CMT4B3 is so rare that there are only 14 known cases worldwide. I had better odds of winning the Mega Millions lottery twice than having a child with this disease. I was told to brace myself for what I would read online about CMT4B3, but there was very little information out there. And what I did find was terrifying. Stories of intellectual disability, children becoming wheelchair-bound, or, in the most devastating cases, people being left unable to speak or move.
I couldn’t wrap my mind around this. Here was my sweet three-year-old boy, building with magnets on the floor, and the future I was reading about didn’t match up at all. I think I cried for three days straight. It felt like my world was crashing down around me. This couldn’t be my reality. But it was.
