CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats) is a revolutionary gene-editing technology that allows scientists to make precise changes to an organism's DNA. It works by utilizing Cas9 protein, which acts as a pair of molecular scissors, and a guide RNA molecule that directs Cas9 to the specific location in the genome where the desired changes need to be made. 

On December 8, the U.S. Food and Drug Administration's approval of exa-cel, the inaugural CRISPR treatment, represents a monumental stride in combatting sickle cell disease (SCD). This endorsement not only signifies a pivotal moment in the global fight against SCD, but also establishes the U.S. as the second nation to authorize a CRISPR therapy, following the U.K.'s approval in November.

Sickle cell disease is a genetic disorder characterized by abnormal hemoglobin, the protein responsible for carrying oxygen in red blood cells. People with sickle cell disease have red blood cells that are shaped like a crescent or sickle, which can cause blockages in blood vessels and lead to various complications. 

The treatment involves directing the enzyme Cas9 to the BCL11A gene, deactivating it in bone marrow stem cells, and prompting the production of fetal hemoglobin, restoring red blood cells to a normal round shape. Physicians implement the therapy by editing a patient's own bone marrow stem cells with exa-cel, destroying untreated marrow, and reintroducing the edited cells.