(Reuters) - Sage Therapeutics Inc’s shares tumbled 23 percent on Tuesday after its drug to treat a life-threatening seizure disorder failed to meet the main goal of a key trial, raising concerns about the future of the study.

The late-stage trial was testing Sage’s drug, brexanolone, in patients with super-refractory status epilepticus (SRSE) whose seizures persisted despite earlier treatments.

“The SRSE study showed little signal and we’d be very surprised if Sage continued clinical development in this context,” Leerink Research analyst Paul Matteis wrote in a client note.

SRSE is the most severe form of status epilepticus, under which seizures last for a long time and often recur.

A patient with status epilepticus is initially treated with a class of psychoactive drugs called benzodiazepines. If one does not respond to them, the patient is given anti-seizure drugs.

If the seizure still persists, the patient is placed into a medically induced coma and is given anesthesia along with another line of anti-seizure drugs, under which efforts are made to wean the impact of those three treatments to determine if the seizure has been resolved or not.

In Sage’s trial, brexanolone helped 43.9 percent of patients wean off medically induced coma without seizures returning for 24 hours, versus 42.4 percent in patients given placebo and standard-of-care treatment.

SRSE accounts for about 25,000 to 41,000 cases each year in the United States and there are currently no treatments approved by the U.S. Food and Drug Administration for the disorder, Sage said.

The company’s shares, which closed at $88.52 on Monday, were down at $68.35 in premarket trading on Tuesday.

Sage is also evaluating the drug for use in severe postpartum depression and essential tremor.

In July last year, Sage said the drug alleviated symptoms of severe postpartum depression, meeting the main goal of a mid-stage study.

(The story has been updated to correct “July” in the last paragraph to “July last year”)