Human endogenous retroviruses that colonized vertebrate DNA millions of years ago have long been dismissed as junk DNA, but researchers now know that they may play important roles in cancer, neurodegeneration, and other ailments.

Researchers repurpose the CRISPR machinery to turn whole classes of transposable elements on or off.

Clinical trials that target human endogenous retroviruses to treat multiple sclerosis, ALS, and other ailments are underway, but many questions remain about how these sequences may disrupt our biology.