Sen. Charles Grassley (R-Iowa) wants to know why a questionable stem cell treatment that might have blinded three patients appeared on a government list of clinical trials.

The Senate Judiciary Committee chairman is asking the Department of Health and Human Services and the Food and Drug Administration for an update on its investigation into U.S. Stem Cell Clinic—three macular degeneration patients went blind after undergoing an unapproved treatment there. The company had listed its offering on ClinicalTrials.gov, and Grassley is asking about the propriety of that.

“There’s good reason to focus on that business, but I also think what...