Darci and Robert Torres still have difficulty talking about the 2009 death of their 3-month-old daughter, Alia. They fed her, put her down to sleep, and a half hour later, she was unresponsive in her bassinet.
"It's hard to go back there — it's so painful," said Darci, a 42-year old mother of four from Stockton, California. "How does a perfectly healthy baby fall asleep and not wake up?"
The Torreses were experienced parents and educated about sudden infant death syndrome: Alia slept on her back, the crib was free from blankets that might obstruct her breathing, and neither smoked.
But now, one scientist has a bold, new theory for why an estimated 3,500 babies a year succumb to SIDS, a mysterious and traumatic event that haunts parents for decades — inner ear dysfunction. (Tweet This)
Dr. Daniel Rubens, an anesthesiologist at Seattle Children's Hospital, had a hunch: If the part of the ear that controls balance is damaged, babies may be unable to reposition themselves when their breathing is compromised.
"We know that the ear is a vital organ," he said. "In the morning, when you wake up, the cells in the vestibular portion of the ear allow you to stand up without falling over. It's very much involved in movement."
The predominant theory about SIDS, based on post-mortem studies, is that it's caused by chemical imbalances in the brain stem that may "destabilize" breathing and heart functions.
But Rubens saw a flaw in that finding.
"The problem is that with an autopsy after an event, you never know for sure if what you are going to find is related to the process they go through when they are dying or the actual cause."
Because SIDS babies are healthy from birth — no major cause of infection, trauma or disease — there has never been a way to determine which ones are at risk.
The 20-year-old Safe to Sleep campaign has cut SIDS death rates in half, but Rubens wants to identify these babies while they are alive, perhaps with the routine hearing test given 48 hours after birth, followed up with imaging of the inner ear.
He was intrigued with a small Rhode Island Department of Health study, which compared the hearing tests of 31 babies who had died of SIDS with those who had survived the first year of life. The SIDS babies scored lower across three sound frequencies in the right ear; a post-mortem of the four SIDS deaths also showed bleeding and damage in the inner ear.
Another 1985 French study also found bleeding and inflammation in the ears of SIDS babies.
Rubens' theory dovetails with animal studies exploring the same theory. Inner ear damage was replicated in healthy mice and those who were deprived of oxygen were unable to reposition themselves.
A healthy human baby will gasp for air and instinctively move its head to breathe. Mice with damaged ears stayed in the same position, breathing "bad air" and died.
He theorizes that in SIDS deaths, both the hearing and balance parts of the ear are damaged, perhaps by a trauma during the birth process. The ear may naturally repair itself.
The critical period for SIDS is two to four months old, then death rates drop; they drop off again at 6 months and SIDS is rarely seen after a year.
Rubens cautions that so far, there is no hearing test for SIDS and a much larger, comprehensive study is needed.
And therein lies the biggest challenge, according to Dr. Carl Hunt, a neonatologist and University of Maryland researcher who is on the board of the American Sudden Infant Death Institute.
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"The kind of data Dr. Rubens is focusing on is really provocative," said Hunt. "But the tricky part is translating that physiology into a practical screening test. That's much more complicated."
Routine detections tests for abnormalities in individual babies would be expensive and perhaps decades away, he added. Both Rubens and Hunt agree that how to monitor babies at risk is also an unanswered question.
Hunt said that while all the latest research points to abnormalities in the brain, the neurological connections between the brain stem and the inner ear "seem to be important."
"Dr. Rubens has certainly stimulated a lot of thought and moving us in a positive direction," said Hunt. "But there is a long way to go to make a difference for individual parents."
As for Darci and Robert Torres, they are helping to raise funds for a three-phase study in England through the SIDS Research Guild, founded by Rubens.