Sudden Infant Death Syndrome (SIDS) may be linked to the build up of carbon dioxide and existing inner ear damage according to a new study in the journal Neuroscience. Author Dr. Daniel Rubens, an anesthesiologist and researcher at Seattle Children's Research Institute, says the finding could help researchers understand the sequence of events and risk factors that lead to SIDS deaths.

"This is potentially an important breakthrough in understanding the biological underpinnings of what may be causing SIDS," Rubens said. "We found that exposure to increasing levels of carbon dioxide and inner ear damage in mice resulted in a lack of movement toward safety and fresh air during sleep. We want to fine tune this discovery and study the connection to carbon dioxide in more detail."

SIDS is defined as the sudden death of an infant that cannot be explained by any other cause after a thorough autopsy, examination of the death scene and review of the clinical history. According to the Centers for Disease Control, SIDS is one of the leading causes of death in infants 1 to 12 months old. About 2,000 babies born in the United States die each year from SIDS.

Research support from a doctor who lost sister to SIDS

Dr. Fred Dore, an internal medicine physician in Bremerton, Washington, is energized by research to crack the medical mystery of SIDS, and for good reason: He recalls the day his little sister, Christine, died of SIDS.

"I was 3 years old and I recall the fireman coming in to see what had happened," Dore said. "I remember how distraught my mother was to find that the healthy baby she'd put to sleep in her crib had died."

His mother, Mary Dore, began to talk to doctors at Seattle Children's about what might have happened and was determined to find a cause. She also began to counsel other families who had lost babies.

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"She and my dad, Fred Dore Sr., wanted to prevent this from happening to other families," he said. "My dad developed legislation that raised awareness about SIDS as a public health issue. Now, when first responders enter a home with a baby, they look for unsafe conditions like sleeping position or a crib with blankets and toys, and those responders can offer safety education for families right there."

His mother founded the Fred H. and Mary S. Dore Foundation as continuing legacy to give back to the community. The foundation supports charitable causes the couple championed over the years, including SIDS research.

"If my mom was alive, I know she would talk Dr. Rubens' ear off and learn whatever she could about this research," Dore said. "Research takes time and funding, and we hope that by telling our story that others might be inspired to support the research as well."

A fine balance of oxygen and carbon dioxide

In the study, Rubens looked at the balance of oxygen and carbon dioxide in the sleeping environment of mice. He and Dr. Nino Ramirez, director of the Center for Integrative Brain Research at Seattle Children's Research Institute, studied combinations of low oxygen and rising carbon dioxide to examine how different levels of the gases impact mice without inner ear damage versus mice with inner ear damage.

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They identified a novel and unexpected finding: Carbon dioxide was not the stimulus for arousal movements during sleep as one would expect. This was the case under natural sleep conditions as well as light anesthesia.

"We observed that a lack of oxygen is the stimulus for the survival movements, and carbon dioxide suppresses that protective response," Rubens said. "This was in addition to the finding that inner ear damage in its own right also suppresses those protective arousal movements."

The link between inner ear damage and carbon dioxide could be key to understanding why seemingly healthy babies, who might have ear damage that's not readily apparent, succumb to SIDS.

Next steps in SIDS research

Rubens recently travelled to Denmark to collaborate with researchers on the next steps that will follow this finding. He is working with Dr. Kasper Kyng and Dr. Tine Brink Henriksen, both clinicians and researchers from the Neonatal Intensive Care Unit at Aarhus University Hospital in Denmark.

"The more we understand these biological mechanisms, the better we can study them and develop ways to identify babies at risk and intervene before a tragic death," Rubens said.

Dore says the family foundation supports the research because they want to continue the work his parents started, and it's a way to pay tribute to Christine's life.

"We visit her grave from time to time," he said. "There's a little stone with her name and a lamb carved into it. Christine was a baby but she accomplished quite a bit in her life by influencing my family to begin this work, and we're proud to carry it on."