Recurrence of sudden infant death syndrome among siblings

Whether or not genetic factors play a role in sudden infant death syndrome represents an important question with respect to both etiology and prevention, and to counselling. An increased recurrence risk would define a high-risk group, essential from a preventive point of view. From an etiological perspective, an increased recurrence risk might indicate either genetic and/or highly stable environmental factors. On the other hand, an identical or only slightly increased recurrence risk would represent strong evidence that genetic factors are not involved in SIDS and would question future search for genetic markers. The acquisition of large materials (a recurrence risk in the population of 6-7 per 1,000,000) necessary to adequately elucidate the issue, represents important methodological problems which have hampered the interpretation of the results to date. Estimates of the risk increase (rate ratios) range from 10 to no significant increase. Data from population-based recurrence studies suggest only a minor, if any, increase, but further elucidation of the issue is needed.