Sudden infant death syndrome and nitrogen metabolism: further development of a hypothesis

A hypothesis suggesting an inducible inability of the enteric bacteria to metabolize urea in infants, resulting in metabolic alkalosis and subsequent respiratory insufficiency, has been proposed as the cause of sudden infant death syndrome (SIDS).

Microbiological cultivation and determination of faecal urease activity and faecal urea content were carried out in 30 cases of unexpected infant deaths out of which 22 were considered to be due to SIDS and eight from other causes. The concentration of nitric oxide (NO) in sealed test tubes was determined after incubation of faeces in normal saline.

The SIDS subjects differed significantly from the control cases in two respects: they had low or no sigmoid faecal urease activity and an unmetabolized sigmoid faecal urea content, whereas the control subjects had normal faecal urease activity and none, or very little, remaining faecal urea. The NO concentration in faeces was correlated with the faecal content of urea in the SIDS cases.

The present findings lend support to the hypothesis of an insufficient metabolism of enteric urea in infants with SIDS.