Medium-chain acyl-CoA dehydrogenase deficiency does not correlate with apparent life-threatening events and the sudden infant death syndrome: results from phenylpropionate loading tests and DNA analysis

Medium-chain acyl-CoA dehydrogenase (MCAD) deficiency is the most common inherited disorder of fatty acid metabolism and typically presents in early childhood as potentially fatal hypoketotic, hypoglycaemic crisis often associated with Reye-like symptoms. Re-investigations of cases of sudden infant death syndrome (SIDS) have revealed in some instances a deficiency of MCAD, suggesting that this metabolic disorder may lead to sudden infant death without prior clinical symptoms. In the present study, we examined 142 infants who had suffered from an apparent life-threatening event (ALTE) or were otherwise considered at risk for SIDS for MCAD deficiency by phenylpropionate loading. In no case excretion of phenylpropionylglycine, the hallmark of MCAD deficiency, was increased. In contrast, 3 out of 55 children with symptoms of metabolic disorders showed increased phenylpropionylglycine excretion, and in all three cases MCAD deficiency was confirmed by DNA analysis. In addition, we investigated 142 cases of sudden unexplained child death and 100 control subjects for the A985G mutation in the MCAD gene which is associated with about 98% of enzyme deficiencies. We found one case of heterozygosity each in the patient and control group. Our data indicate that MCAD deficiency is not a major cause of ALTE and, in agreement with results from similar studies in other countries, its frequency is not increased in children who died of SIDS.