Results of a new study bring closure to countless parents who have endured the nightmare of losing a child to sudden infant death syndrome.

Few words strike fear into the heart of parents like sudden infant death syndrome.

The reason why some apparently healthy newborns unexpectedly die has eluded scientists and doctors — perhaps, until now.

SIDS usually befalls infants before 6 months of age, and during sleep, leaving no certain cause of death.

Results of a new study, appearing in the June issue of the Lancet’s eBioMedicine journal, bring closure to countless parents who have endured the nightmare of losing a child to SIDS, pointing to a lower level of a blood enzyme as the cause.

“These families can now live with the knowledge that this was not their fault,” said lead researcher Dr. Carmel Harrington, of the Children’s Hospital at Westmead in New South Wales, Australia, in an interview with the Australian Broadcasting Association.

“Nobody could tell me [why],” Harrington recalled of the moment she lost her baby to the devastating phenomenon 29 years prior. “They just said it’s a tragedy. But it was a tragedy that didn’t sit well with my scientific brain.”

Each year sees about 3,400 cases of “sudden unexpected infant deaths,” more than a third of which are decidedly due to SIDS, according to the US Centers for Disease Control and Prevention.

Researchers have speculated that SIDS may be the result of a defect in the area of the brain that regulates sleep and breathing. What this looks like: a child who fails to catch their breath during sleep, with a brain that wakes them up for a gasp of air.

Now, there’s new evidence to support this theory, found in blood samples from newborns who died of unknown causes, including SIDS.

Compared to babies who survived sudden death, as well as those who died of other unknown causes, researchers found that babies confirmed as victims of SIDS showed lower levels of one particular enzyme, called butyrylcholinesterase (BChE), which plays an important role in waking up.

Children who lack sufficient BChE are more vulnerable to SIDS because of their reduced ability to wake up naturally.

“Usually, if a baby is confronted with a life-threatening situation, such as difficulty breathing during sleep because they’re on their tummies, they will arouse and cry out,” Harrington explained. “What this research shows is that some babies don’t have this same robust arousal response.”

The mysterious affliction haunts parents — some of whom, despite their best efforts on the advice of doctors, tragically lost their child for seemingly no reason. Previously, physicians told parents to lay their baby on its back to sleep and clear the crib of excess toys or covers that might cause their delicate bodies to overheat or prompt accidental strangulation or suffocation. But still, they couldn’t guarantee the newborn’s safety.

“This finding represents the possibility for the identification of infants at risk for SIDS infants prior to death and opens new avenues for future research into specific interventions,” the authors concluded in their study.

Researchers now hope their work will be used to develop screening protocols for babies at risk of developing SIDS.

In the meantime, the findings allowed Harrington to put the mystery of her son’s death to rest.

She told ABC, “This is the gift that I feel I got for Mother’s Day — because the timing of this is really peculiar to me, that it’s coming on Mother’s Day.”