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What is the RHO gene?
The RHO gene is responsible for production of the protein Rhodopsin, which functions within the retina.(1) Mutations within the RHO gene are associated with 15% of all genetic retinal degeneration conditions in humans, including Retinitis Pigmentosa.(2)
What is the location of the RHO gene?
The RHO gene is found on chromosome 3 in humans, at position 3q22.1, as seen in figure 2.(1) This means it is found on the long arm of chromosome 3.
Figure 2: Structure of Chromosome 3, the RHO gene, the RHO mRNA and location of the P23H mutation.(1)
What is the structure of the RHO gene?
As seen in figure 2, the RHO gene is 6706 nucleotides long and is made up of 5 exons, which are the areas of the DNA which encode the protein.(1) Between these 5 exons are 4 non-coding regions which are cut out during processing of DNA to create a messenger molecule called mRNA, which codes for the protein Rhodopsin.
Mutations in the RHO gene
Over 100 mutations in the RHO gene have been found in patients with Retinitis Pigmentosa.(2) The most common mutation observed is a change in the DNA that codes for the 23rd amino acid of Rhodopsin, resulting in a change from proline to histidine. Other commonly studied mutations are seen in Table 1.
Table 1: Common Mutations Observed in the Rhodopsin Gene and their Impact on the Protein Sequence of Rhodopsin.
What is the P23H Mutation?
The P23H mutation arises due to a nucleotide change within the RHO gene.(3) DNA has four different nucleotides, called A, T, G and C. At nucleotide 68 in the first exon, there is a substitution of the nucleotide C to A, which results in codon 23 in the mRNA coding for histidine instead of proline. Watch the video below to learn more about the P23H mutation.(3,4)
References
1. NCBI [Internet]. Bethesda, MD: National Library of Medicine; 1994. RHO rhodopsin [ Homo sapiens (human)]; Sept 22 2022 [cited 2022 Sept 30]; [about 12 screens]. Available from: https://www.ncbi.nlm.nih.gov/gene/6010?_ga=2.256721291.1608758601.1661168995-1100837187.1661168995
2. OMIM [Internet]. Baltimore, MA: John Hopkins University; 1996. RETINITIS PIGMENTOSA 4; RP4; March 24 2021 [cited 2022 Sept 30]; [about 20 screens]. Available from: https://www.omim.org/entry/613731?search=Retinitis%20pigmentosa&highlight=pigmentosa%20retiniti
3. Dryja TP, McGee TL, Reichel E, Hahn LB, Cowley GS, Yandell DW, Sandberg MA, Berson EL. A point mutation of the rhodopsin gene in one form of retinitis pigmentosa. Nature [Internet]. 1990 [cited 2022 Oct 10];343(6256):364-366. Available from https://www.nature.com/articles/343364a0.pdf
4. OpenStax College. The genetic code [Internet]. Houston Texas: Rice University; 1999. Figure 15.4, This figure shows the genetic code for translating each nucleotide triplet in mRNA into an amino acid or a termination signal in a nascent protein. Available from: https://openstax.org/books/biology/pages/15-1-the-genetic-code
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