Some genetic diseases are more straightforward than others. In cases like cystic fibrosis or Marfan syndrome, a mutation makes a gene defective, and that causes symptoms in a patient that are characterized as a disease. But other kinds of genetic diseases can involve a complex interplay of genes and sometimes, environmental factors, that all work together to create symptoms in a patient. Heart disease and type 2 diabetes are examples of complex diseases.
When using a tool like CRISPR, making a single gene edit can be all that’s necessary to produce or rescue a disease phenotype, but for studying complex diseases a more refined tool is needed. Scientists at UCSF created altered versions of CRISPR so that genes can be manipulated in other ways; CRISPRi can lower gene expression levels, and CRISPRa can activate genes, as explained in the video.