Dr. Carmel Harrington's infant son died in his sleep 29 years ago. The cause was SIDS: sudden infant death syndrome.
SIDS is more a statement of what doctors didn't know than what they did. Describing her reaction, Dr. Harrington said, “It took me about two years before I could really take a breath again, and at that point, I thought I actually want to find out why he died.”
Last week, Dr. Harrington and her collaborators published results in The Lancet that may explain SIDS.
SIDS is formally described as when a seemingly healthy infant, aged 3 to 52 weeks, dies without an apparent cause. The death typically occurs during sleep.
Public health campaigns have reduced SIDS by about half through encouraging back-sleeping, removing items from cribs and discouraging smoking during pregnancy. Despite this recent improvement, SIDS is still the fourth-leading cause of infant deaths in the U.S. Most of the other common causes involve birth defects or pregnancy complications.
The current, rough understanding of SIDS is that three factors, in combination, lead to death. Those three factors are a vulnerable infant, a dangerous period in the infant's development and some outside stressor.
The public health efforts, such as backside sleeping, were concentrating on reducing the outside stressors. The current results aim to identify infants who are vulnerable.
In this new study, the scientists determined that infants who had died from SIDS consistently had a low level of a specific brain enzyme. The hope is that by testing newborns for this enzyme, we could identify those at higher risk for SIDS and take appropriate action.
The details are worth considering, in part because of how studying a small group can represent a huge breakthrough.
The scientists analyzed blood samples of 26 newborns who later died from SIDS. The scientists are from The Children's Hospital in New South Wales, Australia. The blood was standard samples taken from all newborns. The samples were identified and analyzed after the infant deaths.
The scientists carefully matched the samples with 254 equivalent samples from living infants. The goal was to compare the levels of the enzyme BChE in SIDS victims and living infants.
For a variety of reasons, the scientists had already suspected that low levels of BChE were related to SIDS. A complication, however, arises from the blood test.
These blood samples are the standard heel prick done shortly after birth and stored on a filter paper. The samples were stored and tested, in some cases, years later. The measurable BChE on the filter, however, can decrease over time.
The scientists aimed to correct for this effect by choosing blood samples from living infants who were born the same day as each SIDS case. As a further check, the scientists also analyzed samples from 30 infants who had died from non-SIDS causes and 291 date-matched living infants.
The results were dramatic. SIDS cases had significantly lower amounts of BChE than living infants, 5.6 compared to 7.7 enzyme milliunits per liter. Said another way, the measured BChE was almost always lower in the SIDS cases than the date-matched living infants.
There are many follow-up questions. What is the connection between BChE and SIDS? The scientists suspect that BChE is related to an infant's ability to wake themselves up when something is going wrong.
SIDS may happen when an infant has a low level of BChE and, during sleep, has trouble breathing. A typically developing infant would wake up and solve the problem. Perhaps the low level of BChE may stop that waking-up process.
If that scenario is true, then scientists should be able to trace out the exact chemical connections between BChE and waking up. There is a lot of unknown about what BChE does, however, so this story could be wrong.
Another follow-up question is how we can best use BChE tests to prevent SIDS. Thinking broadly, newborns can be tested for low levels of BChE. Those identified as high-risk can then be targeted for some special attention.
It is unclear, however, what special attention is appropriate. We also do not know how many healthy infants would be incorrectly identified in a test for low BchE levels.
These are the sorts of public health questions that will be answered with follow-up studies. Those studies are justified now because of this result. In some ways, studying the blood samples from 26 infants may seem like a small thing. When carefully done, however, it can give us a direction to follow to solve SIDS.
It is impossible for me to imagine losing an infant son as Dr. Harrington, the lead scientist, did. For her to channel those feelings into the 29-year quest toward finding the cause of SIDS is amazing and heroic.
Christer Watson, of Fort Wayne, is a visiting assistant professor of physics at Purdue University Fort Wayne. Opinions expressed are his own. He wrote this for The Journal Gazette, where his columns normally appear the first and third Tuesday of each month.