The quest for the mechanisms of the sudden infant death syndrome: doubts and progress.

THE LEADING CAUSE of mortality during the first year of life, after the neonatal period, is the sudden infant death syndrome (SIDS), also known as cot or crib death.' Its incidence is close to 2 per 1000 live births in most countries, although in some, e.g., the Scandinavian countries, it is markedly lower. It is usually defined as the sudden death of any infant or young child, which is unexpected by history, and in which a thorough postmortem examination fails to demonstrate an adequate cause for death. Because of the high incidence , the catastrophic impact on the affected families , the mystery still surrounding these deaths, and the unsolved scientific problem, SIDS represents a major challenge for contemporary medicine. Prevention of a given event, sudden death in this case, requires an adequate understanding of the mechanisms involved. With regard to SIDS, these mechanisms remain elusive. Here I will discuss some of the actual difficulties and methodologic problems in the research on SIDS and then analyze the respiratory and cardiac theories. The latter will be presented in greater detail, which is not meant to reflect its more prominent role, but rather my area of expertise and my role as one of its proponents.2 A difficult target. Among the many intriguing aspects of SIDS, one certainly is the mixture of hard and soft scientific data on this disorder, as evidenced by critical review of the published studies. This results largely from the involvement-quite unusual in medicine-of investigators with such diverse backgrounds that all too often the interested audience does not have the expertise necessary to recognize potential weaknesses and to identify wrong conclusions. The remarkable lack of documented information is accompanied by a huge number of proposed theories. It is worth recalling that, as stated by Peter Froggatt, "the theories of the accredited scientist and of the quack are alike to the eyes of the gullible beholder."3 There is a consensus that SIDS is multifactorial, i.e., that different mechanisms and causes are involved ; this, however, does not mean that they are all equally important. Indeed, it is very likely that the majority of the proposed hypotheses accounts for a small fraction of SIDS and that most of SIDS deaths are the result of a few critical mechanisms. The respiratory and cardiac disorders are, on logical grounds, probably those involved more often. General problems. Since SIDS is a disease in which …