Genetics · MU Sofia

35. Monogenic Ocular Diseases: Retinitis Pigmentosa, Congenital Color Vision Disorders, Cataracts, Aniridia

Covers four inherited eye disorders in turn: retinitis pigmentosa with its inheritance patterns, genes, fundoscopic signs and management, congenital colour vision defects with a table of protanopia, deuteranopia and tritanopia, hereditary cataracts with their genes and clinical features, and aniridia linked to PAX6, including the WAGR syndrome association and renal screening advice.

Inside: 5 sections · 9 labelled pictures · 1 table · 16 flashcards · 5 min

Topic 35 of 65 in the MU Sofia syllabus for Genetics (Medicine, Year 3). The free AceMed note covers it in 5 sections, about 654 words (5 min of reading), with 16 flashcards.

In this note

  1. Monogenic Ocular Diseases: Retinitis Pigmentosa, Congenital Color Vision Disorders, Cataracts, Aniridia
  2. I. RETINITIS PIGMENTOSA (RP)
  3. II. CONGENITAL COLOR VISION DISORDERS
  4. III. CONGENITAL AND HEREDITARY CATARACTS
  5. IV. ANIRIDIA

Monogenic Ocular Diseases: Retinitis Pigmentosa, Congenital Color Vision Disorders, Cataracts, Aniridia

Monogenic ocular diseases are inherited disorders caused by mutations in genes essential for retinal photoreceptors, ocular development, lens transparency, or visual signal processing. They may present at birth or later in life and can be isolated eye disorders or part of multisystem syndromes.

The most important monogenic eye diseases include:

  • Retinitis pigmentosa
  • Congenital color vision disorders
  • Congenital or hereditary cataracts
  • Aniridia

I. RETINITIS PIGMENTOSA (RP)

Retinitis pigmentosa (RP) is a group of inherited retinal dystrophies characterized by progressive degeneration of photoreceptors, primarily rods, followed later by cones. This leads to night blindness, progressive visual field constriction, and eventual loss of central vision.

Genetic and Molecular Basis

  • Inheritance patterns:
  • Autosomal dominant (AD) – milder, later onset
  • Autosomal recessive (AR) – earlier, more severe
  • X-linked recessive (XL) – most severe
  • Genes involved:
  • RHO (rhodopsin) – common AD form
  • USH2A, ABCA4, PDE6A/B – AR forms
  • RPGR – X-linked forms
  • Protein functions affected:
  • Phototransduction cascade
  • Ciliary transport in photoreceptors
  • Structural integrity of rods and cones

Pathophysiology

  1. 1. Primary degeneration of rod photoreceptors → impaired scotopic (night) vision.
  2. 2. Progressive loss of rods leads to night blindness (nyctalopia).
  3. 3. Secondary degeneration of cones → loss of peripheral and later central vision.
  4. 4. Accumulation of pigment in retina → characteristic bone-spicule pigmentation.
  5. 5. Progressive retinal thinning and optic disc pallor.

Clinical Features

  • Night blindness (often first symptom).
  • Progressive tunnel vision (peripheral field loss).
  • Reduced visual acuity in late stages.
  • Photophobia in some patients.

Fundoscopic findings:

  • Bone-spicule pigmentation.
  • Attenuated retinal vessels.
  • Waxy pallor of optic disc.

Diagnosis

  • Electroretinography (ERG): reduced or absent rod responses.
  • Visual field testing: concentric constriction.
  • Fundoscopy: pigmentary changes.
  • Genetic testing: identifies causative mutation.

Management

  • No curative therapy.
  • Vitamin A supplementation (in selected cases, under supervision).
  • Low-vision aids.
  • Retinal implants and gene therapy (e.g., RPE65) in selected patients.

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