Inherited retinal disease (IRD) is the second most common cause of blindness in childhood, and the leading cause among working age adults in England and Wales. No effective treatment for IRDs exists, however, early gene therapy trials are showing promise.
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Considering there are over 20 known IRDs, we have chosen to provide an overview of the 7 most important diseases to learn about for the Duke-Elder exam. A summary table has been included at the end for your revision.
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RP is the most common IRD. Also known as the rod-cone dystrophies (RCDs), RP is caused by primary loss of rod photoreceptors, and later in life, secondary loss of cone photoreceptors and degeneration of the retinal pigment epithelium (RPE). RP classically presents with night blindness + progressive visual loss. Its prevalence is ****1 in 3000-5000.
Inheritance
RP is a collection of many genetic disorders; RP can be an isolated sporadic disorder, or inherited as autosomal dominant (AD), autosomal recessive (AR), or X-linked (XL). The following genes are most common for these different modes of inheritance:
Mutations in the RHO gene on chromosome 3, which codes for rhodopsin, are the commonest.
〜2% of mutations are in the RPE65 gene, but this is an important gene to remember as gene therapy trials targeting this gene are underway.
Presentation