What Happened
- Researchers have developed PERT (Prime Editing-mediated Readthrough of premature Termination codons), a disease-agnostic genome editing strategy that can potentially treat multiple genetic disorders with a single editing agent.
- PERT targets nonsense mutations — a class of mutations that halt protein production prematurely and cause approximately one-third of genetic diseases.
- Among the 200,000 disease-causing mutations documented in the ClinVar database, 24% are nonsense mutations.
- The approach was tested in human cell models of Batten disease, Tay-Sachs disease, and Niemann-Pick disease type C1, and in a mouse model of Hurler syndrome.
- The technology restored protein production and alleviated disease symptoms with no detected off-target edits or toxicity.
- The study was published in Nature and was conducted by researchers at the Broad Institute.
Static Topic Bridges
Prime Editing — Next-Generation Genome Editing
Prime editing is a precision genome editing technology developed by David Liu's laboratory at the Broad Institute (first published in Nature, 2019). Unlike CRISPR-Cas9 which creates double-strand DNA breaks, prime editing introduces only single-strand nicks, significantly reducing the risk of unwanted insertions and deletions. Prime editing has been described as a "search-and-replace" tool for the genome.
- Uses a Cas9 nickase (modified Cas9 that cuts only one DNA strand) fused to a reverse transcriptase enzyme, forming a prime editor (PE)
- Guided by a prime editing guide RNA (pegRNA) that contains both the target-binding sequence and the template for the desired edit
- Can make all 12 types of point mutations (transitions and transversions), as well as small insertions and deletions
- Does not require double-strand breaks (unlike CRISPR-Cas9) or donor DNA templates (unlike HDR-based editing)
- PM359 (Prime Medicine) became the first prime editor to enter clinical trials in 2024 for chronic granulomatous disease
- In December 2025, two patients treated with PM359 were reported "effectively cured"
- Key advantage: Lower rates of indel byproducts (unwanted insertions/deletions) compared to conventional CRISPR
Connection to this news: PERT leverages prime editing's precision to install a suppressor tRNA that can read through premature stop codons, extending prime editing's therapeutic reach from correcting individual mutations to addressing an entire class of genetic defects with a single treatment.
Nonsense Mutations and Suppressor tRNAs
A nonsense mutation is a point mutation in DNA that converts an amino acid-coding codon into a premature stop codon (UAG, UAA, or UGA), causing the ribosome to terminate protein translation early and produce a truncated, non-functional protein. Suppressor tRNAs (sup-tRNAs) are modified transfer RNA molecules that can recognise premature stop codons and insert an amino acid instead, allowing the ribosome to continue translation and produce a full-length functional protein.
- Nonsense mutations account for approximately 11-24% of all known disease-causing mutations in humans
- Three types of stop codons: UAG (amber), UAA (ochre), UGA (opal)
- PERT uses prime editing to permanently convert a dispensable endogenous tRNA gene into an optimised suppressor tRNA
- The approach is disease-agnostic — the same sup-tRNA can rescue nonsense mutations across different genes and diseases
- Traditional approaches require developing a separate editing agent for each specific mutation — PERT bypasses this with a single composition of matter
- The ClinVar database (maintained by NCBI) catalogues over 200,000 disease-causing mutations, of which 24% are nonsense mutations
- Diseases caused by nonsense mutations include cystic fibrosis, Duchenne muscular dystrophy, beta-thalassemia, and many rare lysosomal storage disorders
Connection to this news: PERT's ability to install a permanent suppressor tRNA that reads through premature stop codons regardless of which gene is affected represents a paradigm shift from mutation-specific therapies to a universal platform that could treat thousands of distinct genetic diseases.
Gene Therapy and Rare Diseases — Regulatory and Ethical Framework
Gene therapy involves introducing, altering, or replacing genetic material within a person's cells to treat disease. India's regulatory framework for gene therapy falls under the Drugs and Cosmetics Act, 1940 (for clinical trials) and the Environment Protection Act, 1986 (for genetically modified organisms). Globally, gene therapies face challenges of cost, delivery, and equitable access.
- India's gene therapy regulation: Indian Council of Medical Research (ICMR) National Ethical Guidelines for Biomedical and Health Research (2017)
- The Genetic Engineering Appraisal Committee (GEAC) under MoEF&CC oversees GMO approvals
- Global rare disease prevalence: approximately 300 million people worldwide affected by over 7,000 rare diseases
- India's National Policy for Rare Diseases (2021, revised): categorises diseases into three groups based on treatment cost and availability
- India's National Registry for Rare Diseases maintained by ICMR
- Approved gene therapies globally: Luxturna (vision loss), Zolgensma (spinal muscular atrophy), Casgevy (sickle cell disease — first CRISPR-based therapy, approved 2023)
- Casgevy (exagamglogene autotemcel) was jointly developed by CRISPR Therapeutics and Vertex Pharmaceuticals
Connection to this news: PERT's disease-agnostic approach could be transformative for rare disease treatment, where the small patient populations for each individual disease make bespoke gene therapy development economically unviable — a single PERT treatment could potentially address thousands of conditions caused by nonsense mutations.
Key Facts & Data
- PERT: Prime Editing-mediated Readthrough of premature Termination codons
- Nonsense mutations: cause ~one-third of genetic diseases
- ClinVar database: 200,000+ disease-causing mutations; 24% are nonsense mutations
- Diseases tested: Batten disease, Tay-Sachs disease, Niemann-Pick type C1 (human cells), Hurler syndrome (mouse model)
- Prime editing first published: 2019 (David Liu lab, Broad Institute)
- PM359: first prime editor in clinical trials (2024) for chronic granulomatous disease
- Rare diseases globally: ~300 million people, 7,000+ diseases
- India's National Policy for Rare Diseases: 2021 (revised)
- First CRISPR-based approved therapy: Casgevy (2023) for sickle cell disease
- Study published in: Nature