The thymus, suffocation, and sudden infant death syndrome--social agenda or hubris?

A Fresh Look at the History of SIDS

Sudden infant death syndrome (SIDS) became a named entity in 1969 and the term has been used to certify sudden unexpected infant deaths meeting certain demographic, epidemiologic, and pathologic criteria. Since it is a diagnosis of exclusion, there is inherent imprecision, and this has led the National Association of Medical Examiners to recommend that these deaths now be classified as "undetermined." This historical review article briefly analyzes anecdotal instances of SIDS described centuries ago as overlying, smothering, infanticide, and suffocation by bedclothes followed by a more detailed review of "thymic" causes (i.e., thymic asthma and status thymicolymphaticus) popular in the late 1800s and early 1900s. Before the 1950s, such cases were also often categorized as accidental mechanical suffocation. In the 1940s and 1950s, forensic studies on infants dying unexpectedly revealed a typical pattern of autopsy findings strongly suggestive of natural causation and, after 1969, cases meeting the appropriate criteria were usually categorized as SIDS, a term embraced by the public and by advocacy groups. Research conducted after the 1960s identified important risk factors and generated many theories related to pathogenesis, such as prolonged sleep apnea. The incidence of SIDS deaths decreased sharply in the early 1990s after implementing public awareness programs addressing risk factors such as prone sleeping position and exposure to smoking. Deletion of cases in which death scene investigation suggested asphyxiation and cases where molecular autopsies revealed metabolic diseases further decreased the incidence. This historical essay lays the foundation for debate on the future of the SIDS entity.

Organ weights in cases of sudden infant death syndrome: a German study

Despite its decreasing incidence, sudden infant death syndrome (SIDS) still remains an important cause of death in infancy. Since Felix Platter described the case of a child suffocated because of a massive goiter (Platter E. Suffocatio a struma interna abscondita, circa iugulum. Observationum in hominis affectibus plerisque corpori et animo, functionum lesione, dolore, aliave molestia et vitio incommodantibus. Libris tres, Part IX. Basel: König and Brandmylieri; 1614), many authors have attempted to verify the existence of a correlation between the dimensions of organs of infants and SIDS. The lack of recent published norms and the difficulty in finding a suitable control group by which to compare the cases of SIDS shows the importance of this study.This article presents the organ weights of 209 male and 132 female babies whose cause of death was SIDS. The data have been collected from 2 different studies: the Westphalian Cot Death Study from 1990 to 1994 and the German National Study on SIDS from 1998 to 2001. The organ weights increased from month to month during the first year of life showing a tendency towards higher weights in males compared with females (these are, however, not statistically significant). No significant differences compared with the recently published data of Thompson and Cohle, J Forensic Sci. 2004;49:575-585 were found.The heart weights were compared with a control group of 47 babies (21 females, 26 males) died because of both natural and unnatural causes. The weight of the organs that presented macro-microscopical pathologic changes was excluded.The weights of the heart were also compared with those published by Schulz and Giordano, Arch Pathol. 1962;74:464-471 and Kelmanson, Eur J Pediatr. 1996;155:440-444. This comparison showed minor differences which are discussed in the article. We suggest that organ weights obtained in SIDS cases can be used as norms in the first year of life.

Histochemical and molecular overview of the thymus as site for T-cells development

The thymus represents the primary site for T cell lymphopoiesis, providing a coordinated set for critical factors to induce and support lineage commitment, differentiation and survival of thymus-seeding cells. One irrefutable fact is that the presence of non-lymphoid cells through the thymic parenchyma serves to provide coordinated migration and differentiation of T lymphocytes. Moreover, the link between foetal development and normal anatomy has been stressed in this review. Regarding thymic embryology, its epithelium is derived from the embryonic endodermal layer, with possible contributions from the ectoderm. A series of differentiating steps is essential, each of which must be completed in order to provide the optimum environment for thymic development and function. The second part of this article is focused on thymic T-cell development and differentiation, which is a stepwise process, mediated by a variety of stromal cells in different regions of the organ. It depends strongly on the thymic microenvironment, a cellular network formed by epithelial cells, macrophages, dendritic cells and fibroblasts, that provide the combination of cellular interactions, cytokines and chemokines to induce thymocyte precursors for the generation of functional T cells. The mediators of this process are not well defined but it has been demonstrated that some interactions are under neuroendocrine control. Moreover, some studies pointed out that reciprocal signals from developing T cells also are essential for establishment and maintenance of the thymic microenvironment. Finally, we have also highlighted the heterogeneity of the lymphoid, non-lymphoid components and the multi-phasic steps of thymic differentiation. In conclusion, this review contributes to an understanding of the complex mechanisms in which the foetal and postnatal thymus is involved. This could be a prerequisite for developing new therapies specifically aimed to overcome immunological defects, linked or not-linked to aging.

Sudden infant death—focus subject of medico-legal research

The compilation of research activities concerning SID in the field of legal medicine could only choose those out of a great abundance of high-quality examinations which represent applied research. By this they have contributed either to the clarifying of the aetiology which has not been cleared up or to the prophylaxis. For this looking through in a widest sense the basic approach was to consider SID being the result of an intrinsic and/or extrinsic disturbance of the modulation of respiratory regulation of the infant. This namely means a metabolic disturbance of respiratory neurons. One must not share this opinion even if it is given a certain plausibility by newer physiological examinations. But this also means that some examinations did not receive the acknowledgement which they would have received if there had been an immunological approach. The compilation was completely done without a presentation of the primary crisis intervention and the long-term care as being a fundamental medico-legal approach. Altogether may be summarized that legal medicine has completely fulfilled its duty to take care of the problem SID and that the examinations did not remain without success.