I am, by no means, an expert when it comes to the science of RP, but I want to try to explain the bits that I do understand. Anyone who has RP and reads my blog, please don’t hesitate to share your knowledge in the comments section; I have a lot to learn.
RP is most often characterized as an inherited disease. There are 3 different inheritance patterns: Autosomal Dominant; in which one parent and one or more children are affected. Autosomal Recessive; in which both parents are carriers, but unaffected, and children can either be affected or just carriers or completely unaffected. X-Linked; in which the disease is passed only from the mother and affects sons, more frequently and severely, than daughters. More than 60 gene mutations have been linked to these inheritance patterns. More than 20 are associated with the Autosomal Dominant pattern, with mutations in the RHO gene accounting for 20 to 30 percent of all cases. At least 35 genes have been associated with the Autosomal Recessive patterns, with mutations in the USH-2A gene accounting for 10 to 15 percent of all cases. At lease 6 gene mutations are thought to cause X-Linked RP, with mutations in the RPGR and RP2 genes together, counting for most cases. My understanding is that identifying the specific gene mutations is what will enable researchers to create gene therapies for all 3 types of RP.
There is a fourth group of people affected with RP: In 10 to 40 percent of all cases of RP, only one family member is affected; in these families, the disorder is described as Simplex. It is difficult to determine the inheritance pattern of Simplex cases because those affected can have either no affected relatives, or be unaware of other affected relatives. Some Simplex cases can also result from a new gene mutation that is only present in the affected individual. It seems to me that these Simplex people are kind of screwed; if no inheritance pattern or specific gene mutations can be located, then gene therapies can’t be applied to these patients. I am, most likely, part of this Simplex group.
As far as I know, I am the only person in my family with RP. My father’s father may have exhibited some signs that he had trouble with his eyes (primarily light sensitivity), but I think I was just trying to make sense of why I ended up with this crazy disease. I wrote a poem about it that was published last year in Foxglove Journal. Is it possible that I have Autosomal Recessive RP? Possible, but unlikely. And, my mom died 30 years ago, so there is no way I could find out if she was a carrier.
I just read about the Simplex cases this morning, but now Dr. Saraff’s explanation about me having the most common form of RP, and his not recommending genetic testing, makes more sense. I feel like I am on an RP island, but apparently, there are a lot of people on the island with me. In some ways, my situation seems grim, but I don’t feel grim. I still have hope, but after my appointment last week, I put it back on a shelf, out of sight and reach, which is exactly where I need it to be.