Retinal Diseases: RNA therapeutics show promise but is India ready?

According to the World Health Organisation, more than 2.2 billion people worldwide experience some forms of vision impairment. 

• An estimated 5.5 million people suffer from IRDs around the world, with a prevalence rate of one in 3,450.
• Studies have revealed significantly higher prevalence of such cases in India
  • one in 372 individuals in rural South India,
  • one in 930 in urban South India, 
  • and one in 750 in rural Central India affected by these conditions.

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What are Inherited Retinal Diseases (IRDs)?

• IRDs are genetic disorders causing progressive vision loss, often leading to blindness.
• Caused by mutations in 300+ genes responsible for retinal function.
• Some individuals lose vision early, while others experience gradual deterioration.
• Early intervention can slow or prevent blindness in some cases.

How do Genes Affect Vision?

• The body is made up of cells, each containing a nucleus with chromosomes made of DNA.
• DNA contains genes, which provide instructions for making proteins essential for body functions.
• A change (mutation) in a gene can cause proteins to function incorrectly or be missing.
• Faulty proteins in the retina lead to IRDs and vision loss.

Risk Factors for IRDs

IRDs follow different inheritance patterns:

• Autosomal Dominant: The defective gene is located on an autosome (non-sex chromosome).
  • A person inherits one faulty dominant gene from a parent and one normal gene from the other.
  • The faulty dominant gene causes the disorder.
• Autosomal Recessive:  Both copies of the gene (one from each parent) must be defective. 
  • Parents are usually asymptomatic carriers.
    • 25% chance of inheriting the disease if both parents are carriers.
• X-linked Disorders: The defective gene is located on the X chromosome. 
  • Males (XY) are more severely affected as they have only one X. 
  • Females (XX) may be carriers or show milder symptoms.
• Mitochondrial Inheritance: Mutations occur in mitochondrial DNA (mtDNA), inherited exclusively from the mother (sperm do not contribute mitochondria).
  • Can affect multiple organs, including the eyes.

What is RNA-Based Therapy?

• RNA-based therapies offer a safer alternative to gene therapy as they do not alter DNA permanently.
• These therapies temporarily modify gene expression, reducing long-term risks.

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Types of RNA-Based Therapies

• Antisense Oligonucleotides (ASOs)
  • Used successfully for spinal muscular atrophy and Duchenne muscular dystrophy.
  • Being tested for Stargardt disease, Leber congenital amaurosis, and retinitis pigmentosa.
• RNA-Editing with ADAR Enzymes
  • Corrects specific mutations at the RNA level.
  • Can restore protein production in retinal cells without altering DNA.
• Suppressor tRNA Therapy
  • Bypasses stop-codon mutations that disrupt protein synthesis.
  • Helps in producing full-length proteins to restore retinal function.
• Small Molecule RNA Therapy (PTC124/Ataluren)
  • Used for cystic fibrosis and Duchenne muscular dystrophy.
  • Clinical trials underway for treating aniridia (a rare eye disease).

India’s Role in Precision Medicine

• What is Precision Medicine?
  • It tailors treatments based on a person’s genetics, lifestyle, and environment.
  • Aims for personalized care instead of a one-size-fits-all approach.
• Need for Genetic Research in India
  • Over 300 genes are linked to IRDs, but India lacks large-scale studies on genetic mutations in its population.
  • No major study (500+ patients) has mapped genetic variations in Indian IRD patients.
  • Identifying common genetic mutations is crucial for developing effective treatments.
• Challenges in India
  • Genetic variations differ across communities in India, making research complex.
  • Barriers include:
    • Low awareness among doctors and patients.
    • Limited access to genetic counseling.
    • Insufficient research funding.
    • Lack of diagnostic infrastructure, especially in rural areas.

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