Sudden infant death syndrome and the central nervous system: a review of the triple-risk theory
Hogan, Matthew Charles
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Sudden infant death syndrome (SIDS) is the devastating condition in which an infant suddenly and unexplainably passes away over the course of sleeping. This is an unfortunate situation that many new parents dread every night as they lay their newborns to rest. SIDS is the leading cause of death in infants aged from one month to one year, and the medical world still does not fully understand what causes it. However, the triple-risk theory is a new model that sets out to explain the pathology of this syndrome through the combination of genetic vulnerabilities, a critical time period, and external stressors. This thesis summarizes the current research in the realm of the central nervous system (specifically the cerebellum and brainstem) as a means of evaluating the validity of this new model. The analyzed literature concentrated on a few important topics, such as proven risk factors, evidence of homeostatic abnormalities, and significant associations with the occurrence of SIDS. It was found that there was central nervous system dysfunction on most levels, including: damaged Purkinje cells in the cerebellum, malformations of the human choroid plexus, decreased neuropeptide signaling (both orexin and brain-derived neurotrophic factors), malformations of the amino acid neurotransmitters (both excitatory glutamate and inhibitory GABA), and finally significant reductions in the receptor density and activity of the serotonin system. These irregularities were associated, in most studies, with either the prone sleeping position or known maternal nicotine use during pregnancy. In conclusion, the triple-risk model is currently the most accurate description of SIDS, given its reasonable three criteria and present-day research. This is because the studies, and real-life victims, were all concentrated within the critical time period of transition from intra-uterine to extra-uterine life, satisfying the first element of timing. The list of central nervous system dysfunctions found in SIDS cases was compelling enough to fulfill the second factor of inherent vulnerability. Finally, the associations between low oxygen rebreathing and the prone sleep position, or over-heating and tight swaddling displayed a strong relationship with the occurrence of SIDS and satisfied the third and final event, which was the induction of an exogenous stressor. These three factors of the triple-risk model allow for the variations in victim pathology, but still offers a compelling and coherent understanding of the sudden infant death syndrome.