CURRENT TOPIC Biochemical screening in newborn siblings of cases of SIDS

The association between inherited metabolic disorders and the sudden infant death syndrome (SIDS) received considerable attention in the mid to late 1980s. The earlier reports suggested that as many as 5-10% of all cases of SIDS in the UK could be due to metabolic disorders.' 2 More recent publications, however, suggest a more conservative estimate that such disorders probably account for fewer than 3% of all cases of SIDS-5 and thus compare better with the recurrence risk of2% quoted in several studies.6 The only group of inherited metabolic disorders for which there is good evidence that they are responsible for SIDS are those of fatty acid oxidation. The evidence that other inborn errors can present as SIDS is scanty,78 although many defects have the potential to cause unexpected infant death.9 Despite the rarity of these disorders it is important to identify those cases where an inherited defect is the likely cause or contributes to the cause of death or a near miss death in infancy. In many cases of so called SIDS there is a history of illness preceeding death and such cases of sudden unexpected death in infancy are equally if not more important to consider. The finding of fatty change at necropsy' in those infants who have died unexpectedly should stimulate detailed investigation for inherited metabolic disorders. Similarly, paediatricians should consider inherited metabolic disorders in cases of 'near miss' cot death or any patient labelled as having Reye's syndrome and investigate accordingly.'0 If a specific metabolic disorder is identified, all siblings should then be investigated. The situation is less clear if a specific disorder is not identified or inherited metabolic disorders are not strongly suspected. Although whole population newborn screening for certain fatty acid oxidation defects is likely to be possible in the future," it is far from clear at present whether such an approach would satisfy the criteria for population screening and could therefore be justified economically. Currently it is therefore important to consider investigation ofhigher risk groups (that is siblings). This discussion specifically considers the investigation of newborn siblings in those families where a previous sibling has died suddenly and unexpectedly, that is it includes both SIDS and sudden unexpected death in infancy. Biochemical disorders as a possible cause of SIDS Inherited metabolic disorders that are known to be associated with acute life threatening events are all possible causes of sudden unexpected death in infancy.9 In practice the fatty acid oxidation defects are the only group that have been well documented. 12