Chinese scientists have raced ahead in experimenting with gene-editing on humans in the last few years, using a powerful new tool called Crispr-Cas9 to edit the DNA of dozens of cancer patients.

Information gathered by The Wall Street Journal shows one such trial has lost touch with patients whose DNA was altered, alarming some Western scientists who say subjects should be monitored for many years.

In another trial, an Indian man’s cancer improved but he suffered a heart attack and brain stroke; Chinese doctors didn’t investigate the cause, the deceased man’s family said.

Now, these and other Crispr trials are coming under scrutiny for the first time from health authorities in Beijing after a controversial gene-editing announcement in China last month sparked international concern over whether there is adequate regulation and oversight in the country.

Three doctors involved with Crispr trials in China told the Journal they received inquiries from the nation’s science and health ministries in recent weeks asking for details about their trials. Neither ministries responded to requests for comment.