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Mystery of sudden infant deaths may be solved: researchers 

Nov. 8, 2006
Special to World Science  

“Sud­den in­fant death syn­drome” may re­sult from ab­nor­mal­i­ties in the brain stem, a pri­mi­tive brain region that re­gu­lates bas­ic life func­tions, a study has found.

The syn­drome, ab­bre­vi­at­ed SIDS, is the sud­den and un­ex­pect­ed death of in­fants un­der a year old, who are typ­i­cal­ly found to have died in their sleep with no signs of suf­fer­ing. An enig­ma­tic con­di­tion, it strikes 15 of eve­ry 10,000 ba­bies, ac­cord­ing to the Merck Man­u­al of Di­ag­no­s­is and The­rapy.

Cross-sec­tion of the brain stem, a stem­like re­gion that joins the spi­nal cord to the main bulk of the brain, in SIDS in­fants (a­bove) and nor­mal ones (be­low).  SIDS ba­bies were found to have more cells that make and re­lease ser­o­to­nin, par­t­i­cu­lar­ly in an  ar­ea known as the mid­line ra­phé nu­cle­us (blue dots). But the SIDS in­fants al­so had in­suf­fi­cient amounts of two sub­stances that fa­cil­i­tate ser­o­to­nin use, re­search­ers said. (Im­age cour­te­sy Da­vid Pat­er­son, Ph.D., Chil­dren’s Hos­pi­tal Bos­ton)


The new find­ings sug­gest it “is not a mys­tery but a dis­or­der that we can in­ves­ti­gate with sci­en­tif­ic meth­ods, and some day, may be able to iden­ti­fy and treat,” said Han­nah Kin­ney of Chil­dren’s Hos­pi­tal Bos­ton and Har­vard Med­i­cal School in Bos­ton, the stu­dy’s lead au­thor.

The re­search ap­peared in the Nov. 1 is­sue of the Jour­nal of the Amer­i­can Med­i­cal As­so­ci­a­tion.

The brain stem con­trols heart rate, breath­ing, blood pres­sure, tem­per­a­ture and arous­al. The ab­nor­mal­i­ties that Kin­ney and col­leagues iden­ti­fied seem to af­fect its abil­i­ty to use the brain chem­i­cal ser­o­to­nin, they said. 

Ser­o­to­nin plays roles in com­mu­ni­ca­tion be­tween brain cells and in reg­u­lat­ing mood, breath­ing and blood pres­sure.

The find­ings sug­gest the risk of sud­den in­fant death “may great­ly in­crease when an un­derlying pre­dis­po­si­tion com­bines with an en­vi­ron­men­tal risk,” said Du­ane Al­ex­an­der, di­rec­tor the Na­tion­al In­sti­tute of Child Health and Hu­man De­vel­op­ment of the Na­tion­al In­sti­tutes of Health, which funded the stu­dy.

The chief en­vi­ron­men­tal risk to which Al­ex­an­der re­ferred was sleep­ing face down, a rec­og­nized SIDS risk fac­tor.

The re­search­ers com­pared the brain­stems of 31 SIDS vic­tims and 10 in­fants who died of oth­er causes. 

The sci­en­tists found that vic­tims’ brain­stems have less of two sub­stances that fa­ci­li­tate ser­o­to­nin use, com­pared to the num­ber of cells that use it. These en­ablers of ser­o­to­nin use are called the ser­o­to­nin trans­port­er pro­tein and the se­ro­to­nin re­cep­tor 5HT1A.

The re­sult seems to be a short­age of use­able ser­o­to­nin, which changes ba­bies’ re­ac­tions, the sci­en­tists ar­gued.

When ba­bies sleep face-down or have their faces cov­ered by bed­ding, they are thought to re-breathe ex­haled car­bon di­ox­ide, and thus get less ox­y­gen. Nor­mal­ly, the rise in car­bon di­ox­ide ac­ti­vates nerve cells in the brain­stem, the re­search­ers said. These in turn stim­u­late a re­ac­tion that pre­vents as­phyx­i­a­tion.

“A nor­mal ba­by will wake up, turn its head, and start breath­ing faster,” said Kin­ney. In sud­den in­fant death vic­tims, de­fects in the ser­o­to­nin sys­tem may im­pair these re­flexes, with tragic results, she added.


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“Sudden infant death syndrome” may result from abnormalities in the brainstem, a part of the brain that helps control basic life functions, a new study has found. The syndrome, abbreviated SIDS, is the sudden and unexpected death of infants under a year old, who are typically found to have died in their sleep with signs of suffering. It strikes 15 of every 10,000 babies, according to the Merck Manuals Online Medical Library. The new findings suggest it “is not a mystery but a disorder that we can investigate with scientific methods, and some day, may be able to identify and treat,” said Hannah Kinney of Children’s Hospital Boston and Harvard Medical School in Cambridge, Mass., the study’s lead author. The research appeared in the Nov. 1 Journal of the American Medical Association The brainstem controls heart rate, breathing, blood pressure, temperature and arousal. The abnormalities that Kinney and colleagues found appear to affect its ability to use the brain chemical serotonin, they said, which plays roles in communications between brain cells and in regulating mood, breathing and blood pressure. The finding suggests the risk of sudden infant death “may greatly increase when an underlying predisposition combines with an environmental risk,” said Duane Alexander, director the National Institute of Child Health and Human Development at the of the National Institutes of Health, which funded the study. The chief environmental risk to which Alexander referred was sleeping face down, a recognized risk factor for SIDS. The researchers compared the brainstems of 31 SIDS victims and 10 infants who died of other causes. The scientists found that victims’ brainstems have less of a substance that enables serotonin to be used—called serotonin transporter protein—compared to the number of cells that use serotonin. The result seems to be a serotonin shortage that changes babies’ reactions, the scientists argued. When babies sleep face-down or have their faces covered by bedding, they are thought to re-breathe exhaled carbon dioxide, therefore breathing in less oxygen. Normally, the rise in carbon dioxide activates nerve cells in the brainstem, which in turn stimulates a reaction that prevents asphyxiation. “A normal baby will wake up, turn its head, and start breathing faster,” said Kinney, but in sudden infant death victims, defects in the serotonin system may impair these reflexes.