SIDS May Be Linked to Hippocampus Abnormality

An abnormality in the hippocampus was more prominent in infants that died of SIDS than those with explained causes of death.

Sudden infant death syndrome may be linked to an abnormality in the hippocampus, which, through its connection to the brainstem, involves some processes of breathing and cardiac function.

Researchers from Boston Children’s Hospital and Harvard Medical School, along with colleagues from the San Diego Medical Examiner’s office and Baylor College of Medicine studied sections of the hippocampus of 153 infants autopsied as the San Diego Medical Examiner’s office that died from both explained and unexplained causes between 1991 and 2012.

Of the group of infants with unexplained cause of death (including sudden infant death syndrome [SIDS] and other cases), 41.2% had an abnormality in the dentate gyrus, a structure within the hippocampus, characterized by a double layer of nerve cells at certain points along its length. The abnormality, called focal granule cell bilamination, was found in only 7.7% of the explained (control) group. Of the 86 cases classified as SIDS, 43% had the abnormality.

Researchers believe that the abnormality may disrupt the brain’s control of breathing and heart rate patterns during sleep, and also noted that the abnormality is similar to one observed in people with temporal lobe epilepsy.

“The pattern of abnormal changes in the dentate gyrus suggests to us there was a problem in its development at some point in late fetal life or in the months right after birth,” Hannah C. Kinney, MD, study researcher, said in a news release. “We didn’t see any signs of injury to the brain by low oxygen levels in the tissue we examined, such as scarring and loss of nerve cells.”

Kinney and colleagues previously found that infants who died of SIDS had abnormal levels of serotonin, including low levels of serotonin receptors in parts of the brainstem that control breathing, heart rate patterns, blood pressure, temperature regulation, and arousal during sleep. The researchers are now exploring if there is a link between the abnormal serotonin levels and abnormal development of the dentate gyrus in SIDS cases. 


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