Blog vol 4.21. Cannot get away from those Cones and Rods
This past week, we had a family in the office whose close relatives have a history of cone-rod dystrophy. The parents were concerned about their child and the possibility of genetic transmission of a potentially blinding condition. Clearly, this condition can be genetically linked as more than one of their relatives has it and these relatives are siblings. So what does this mean for their child?
There are many variations and types of cone-rod dystrophy (and these are different from rod-cone dystrophies, like retinitis pigmentosa, just to keep you on your toes). Dystrophy can affect the cones alone or it can affect both cones and rods. The rods and cones are the light receptors in the outer retina that take in light and convert it into electrical impulses which finally result in sight. They are critical to the seeing process, so one can imagine the devastation to the vision if there is major damage to these receptors. Cone-rod dystrophies are conditions that are inherited (autosomal recessive) and can start affecting the vision at birth but, more often than not, show up in the later teens.
Thus the question from my patient: how do I know if my child has inherited this condition? An eye exam is a great place to start. Then, in their teens, an electroretinogram can be scheduled to rule out cone or rod deterioration. Genetic testing is also a possibility. Are the parents carriers? Does the child have the gene? Both the parents would have to have the recessive gene. As of today, 35 known gene mutations account for 60 % of the cases - with the most common being the ABCA4 gene. (Learn more
here).
The progression of the disease varies, but it does progress and does lead to severe vision loss. There are currently few effective treatments for these dystrophies. The key becomes optimizing existing vision. A low vision assessment and support from a social worker will help. Cone-rod dystrophy occurs only in 1 out of 20, 000 to 100,000 people worldwide. Having it in your family does increase your risk, how much is the question.
Not a lot of surety for this family though there is no evidence for the second parent being a carrier. Both parents need to be carriers for there to be even a possibility of the child developing cone-rod dystrophy. The child looks great now and most likely will continue to do so. Really, we need to know if the parents are carriers while continuing to monitor the child’s eye health. Peace of mind is the goal. Genetic testing will be the best option, potentially eliminating the concern altogether.
Til next week,
the good doctor
