Research Articles

The human genome contains approximately 20,000 protein-coding genes, yet each cell type expresses only a fraction of these at any given time. Understanding which genes are active, when they are expressed, and at what levels has become central to modern biomedical research. Technologies such as RNA-seq, single-cell transcriptomics, and spatial transcriptomics have revolutionized our ability to map gene expression with unprecedented resolution.

The GTEx (Genotype-Tissue Expression) project has cataloged expression patterns across 54 human tissue types from nearly 1,000 individuals. This resource has revealed that approximately 80% of protein-coding genes are expressed in most tissues, though expression levels vary dramatically. Tissue-specific genes, such as insulin in pancreatic beta cells or hemoglobin in erythroid cells, account for critical biological functions and disease processes.

Epigenetic modifications, including DNA methylation and histone modifications, play crucial roles in regulating gene expression. Recent studies using ATAC-seq and ChIP-seq have identified millions of regulatory elements that control when and where genes are turned on or off. Understanding these regulatory landscapes is essential for interpreting the effects of non-coding genetic variants identified in genome-wide association studies (GWAS).

Since the first CRISPR-based therapy (Casgevy) received FDA approval in December 2023 for sickle cell disease, the field has accelerated dramatically. By early 2026, multiple CRISPR therapies are in late-stage clinical trials targeting conditions from hereditary blindness (Leber congenital amaurosis) to familial hypercholesterolemia and certain blood cancers.

Base editing, which allows precise single-nucleotide changes without creating double-strand breaks, has emerged as a safer alternative for many applications. Verve Therapeutics' base editor targeting PCSK9 for cardiovascular disease prevention showed promising Phase I results, reducing LDL cholesterol by up to 55% with a single intravenous infusion. Prime editing, which can perform all 12 possible base-to-base conversions plus insertions and deletions, continues to be optimized for clinical translation.

Delivery remains a key challenge. Lipid nanoparticles (LNPs) have proven effective for liver-targeted delivery, but reaching other tissues efficiently is an active area of research. Novel approaches including engineered adeno-associated viruses (AAVs), virus-like particles (VLPs), and extracellular vesicles are being developed for tissue-specific CRISPR delivery to muscle, brain, and lung tissue.

1. BRCA1/BRCA2 - These tumor suppressor genes are essential for homologous recombination DNA repair. Pathogenic variants increase lifetime breast cancer risk to 45-85% and ovarian cancer risk to 10-40%. PARP inhibitors exploit BRCA-deficient tumors' inability to repair DNA damage, creating synthetic lethality.

2. TP53 - Known as the "guardian of the genome," TP53 encodes p53, which regulates cell cycle arrest, DNA repair, and apoptosis. Somatic TP53 mutations are found in approximately 50% of all human cancers. Germline mutations cause Li-Fraumeni syndrome.

3. APOE - The APOE e4 allele is the strongest common genetic risk factor for late-onset Alzheimer's disease, increasing risk 3-12 fold. APOE also influences cardiovascular disease risk through its role in cholesterol metabolism. The protective e2 allele is associated with longevity.

4. CFTR - Mutations in this chloride channel gene cause cystic fibrosis, the most common lethal autosomal recessive disorder in European populations. The F508del mutation accounts for approximately 70% of CF alleles. CFTR modulators like elexacaftor/tezacaftor/ivacaftor have transformed CF treatment.

5. KRAS - The most frequently mutated oncogene in human cancers, particularly pancreatic (90%), colorectal (40%), and lung adenocarcinoma (30%). Once considered "undruggable," the development of sotorasib and adagrasib targeting KRAS G12C has opened new therapeutic avenues.