RP2 gene

Overview

Gene (OMIM No.)
Function of gene/protein
  • Protein: Retinitis pigmentosa 2
  • Expressed at the basal body of the photoreceptor connecting cilium
  • Regulates lipid-modified protein transport from the photoreceptor inner segment to the outer segment via the connecting cilium
Clinical phenotype
(OMIM phenotype no.)
Inheritance
  • X-linked recessive
Signs for X-linked RPMale patients
  • Vessel attenuation
  • Extensive and early macular involvement (granular changes, bull’s eye maculopathy and perimacular atrophy) which eventually progresses to macular atrophy
  • Variable peripheral changes (granularity, depigmentation, hyperpigmentation or choroideremia-like appearance without hyperpigmentations)
  • Optic disc pallor
  • High myopia (<-6.00D)
Female carriers
  • Symptomatic carriers display similar phenotypes to male patients with early macular atrophy
  • Asymmetrical disease has been reported
  • High myopia (<-6.00D)
Visual function
  • Onset of nyctalopia and/or peripheral VF loss within the 1st decade of life
  • Rapid rate of VA decline compared to patients with RPGR mutations
  • Central scotoma present in about 50% of patients and often before 12 years of age
  • Rate of VF loss similar to RPGR mutations
  • Most female carriers are asymptomatic but vision can be as severely impaired as male patients
Systemic features
  • No extraocular features reported
Key investigations
  • Full field ERG: rod-cone dystrophy/generalised retinal dysfunction in advanced stages
  • Pattern ERG: Early deterioration
  • FAF: Central and peripheral patches of hypo-AF corresponding to atrophic areas
  • OCT: Early loss of foveal outer retinal layers
Molecular diagnosisNext generation sequencing
  • Targeted gene panels (retinal)
  • Whole exome sequencing
  • Whole genome sequencing
ManagementOcular
Therapies under research
Further information

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Additional information

Pathogenic mutations in RP2 account for 5-20% of XL-RP cases.[1-4]

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Multimodal imaging

Wide field colour fundus photograph (A) and FAF imaging (B) of a patient with hemizygous RP mutation. There are minimal bone-spicules seen on A. FAF imaging shows a well-demarcated area of macular atrophy.
OCT scan through the macula of the same patient showing outer retinal and RPE atrophy. The retinal is significantly thinned at the fovea.

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References

  1.  Sharon D, Sandberg MA, Rabe VW, Stillberger M, Dryja TP, Berson EL. RP2 and RPGR mutations and clinical correlations in patients with X-linked retinitis pigmentosa. Am J Hum Genet. 2003;73(5):1131-1146
  2.  Pelletier V, Jambou M, Delphin N, et al. Comprehensive survey of mutations in RP2 and RPGR in patients affected with distinct retinal dystrophies: genotype-phenotype correlations and impact on genetic counseling. Hum Mutat. 2007;28(1):81-91
  3.  Breuer DK, Yashar BM, Filippova E, et al. A comprehensive mutation analysis of RP2 and RPGR in a North American cohort of families with X-linked retinitis pigmentosa. Am J Hum Genet. 2002;70(6):1545-1554
  4.  Hardcastle AJ, Thiselton DL, Van Maldergem L, et al. Mutations in the RP2 gene cause disease in 10% of families with familial X-linked retinitis pigmentosa assessed in this study. Am J Hum Genet. 1999;64(4):1210-1215
  5.  Lyraki R, Megaw R, Hurd T. Disease mechanisms of X-linked retinitis pigmentosa due to RP2 and RPGR mutations. Biochem Soc Trans. 2016;44(5):1235-1244
  6.  Jayasundera T, Branham KE, Othman M, et al. RP2 phenotype and pathogenetic correlations in X-linked retinitis pigmentosa. Arch Ophthalmol. 2010;128(7):915-923
  7.  Ji Y, Wang J, Xiao X, Li S, Guo X, Zhang Q. Mutations in RPGR and RP2 of Chinese patients with X-linked retinitis pigmentosa. Curr Eye Res. 2010;35(1):73-79
  8.  Kurata K, Hosono K, Hayashi T, et al. X-linked Retinitis Pigmentosa in Japan: Clinical and Genetic Findings in Male Patients and Female Carriers. Int J Mol Sci. 2019;20(6)

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Updated on November 30, 2020
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