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• CRD/RCD
• Posted: 2008-03-07 15:55:24 By maris s
• Which one is a more severe form of RP? and is a non-recordable ERG consistent with CRD or RCD form of RP?
  Please help
  
  Maris

• Re: CRD/RCD
• Posted: 2008-03-07 20:07:07 By Carol C
• My brother has X-linked CRD (cone-rod dystrophy), and I can share a mix of what we have been told by genetic counselors and what I have read on technical retina sites on the web: most CRD is caused by a gene(s) on one of the 22 pairs of autosomes that we all have, and this is considered a different condition than RCD (rod-cone dystophy, same as typical RP). Males and females have 50% risk of inheriting it from an effected parent. The 23rd pair of chromosomes is either XX ( if female) or XY (if male). If a male inherits this gene on the X from his mother, he will be effected and eventually go lose vision completely. If a female inherits this X from either her effected father or her "carrier" mother, she will technically have the condition as well, but as her symptoms can be so mild as to be unnoticable, she is called a carrier, and can pass it to sons and daughters ( an effected male can only pass it to daughters). Generally, X-linked conditions are more severe, with symptoms developing earlier and progressing faster, in the effected males. Our gene rides on this X chromosome, in the "hotspot" for XLRP genes, hence is classified with the RP's but is actually very rare form of CRD ( although more and more families that have thus far been classified with XLRP are being found to actually have XLCRD, so it may turn out to be not-so-rare). Maybe all this distinction is not important, but maybe learning everyone's specific gene mutation will be helpful in learning exactly what is wrong with the message relay between these cells and the brain, thereby helping develop more treatments. In CRD, the cones cells stop functioning first, so symptoms are usually visual acuity problems, trouble distinguishing colors, "day blindness" ( increasing difficulty seeing in bright light- my grandmother frequently wore sunglasses inside the house). Then the problem spreads to the rod cells, causing night blindness and loss of peripheral vision, spreading from the center outwards. My brother has almost no pigment clumps in his retinas, a distinguishing symptom of RP, and his tesing shows more cone involvment than rod involvment. He also had "blind spots" as a teenager, when the hockey puck or baseball would disappear and reappear, making him believe he just wasn't good at sports. He didn't develop trouble seeing in the dark until his late 20's. He also developed cataracts at age 32, and has been told that the back layers of hs eyes have completely atrophied ( ?choroid and RPE? haven't gotten a good explanation of this yet). Carol

• Re: CRD/RCD
• Posted: 2008-03-08 02:21:25 By Darran Z
• I'm not sure what you are asking. These are both types of RP. As Carol pointed out, the RCD (Rod-Cone Dystrophy) is the more tyipcal form of RP and CRD (Cone-Rod Dystrophy) is an atypical form. Most folks with RP have the RCD dealing with the rods being affected first (which is why we have nightblindness and tunnel vision). CRD, the cones are affected first, which explains why their visual acuity is worse but still have some visual field.
  
  But "severity" depends upon the mutated gene. In general, the severity is that X-Linked RP is quite aggressive and severe,then Autosomaal Recessive and then Autosomal Dominant inheritance patterns are the more mild form.
  
  But either one of the two (CRD or RCD) can be severe equally and have quite flat ERGs.
  
  Darran

• Re: Re: CRD/RCD
• Posted: 2008-03-08 12:20:00 By maris s
• Thanks Carol and Darran, i was reseaching about the two and kept wondering which is severe because some of the literature did not say they were forms of RP. I do understand now and thanks again for the detailed explanation.
  Maris