is a rare disorder that results in

is a rare disorder that results in long-chainfatty acids being unavailable for mitochondrial boxidation and ketogenesis. It can present in theneonatal period or infancy with a severe clinical form,typically with convulsions, hypothermia, encephalopathy, cardiomyopathy and liver dysfunction, or with amilder phenotype with episodes of hypoglycaemia andhyperammonaemia during intercurrent illness. Investigations show hypoketonaemia, intermittent dicarboxyluria and hypocarnitinaemia with grossly elevatedacylcarnitines. Enzyme assay or DNA analysis confirmsthe diagnosis. The severe phenotype results in severedisability or death. The less severe phenotype can alsocause significant disability secondary to hypoglycaemiaand/or hyperammonaemia at presentation. We reportthe outcome of two siblings with CACT deficiency. Theindex patient presented at the age of 2 months during arespiratory illness with hypoglycaemia, hyperammonaemia and cardiorespiratory collapse. Acylcarnitineprofiles showed decreased free carnitine but strikingelevations of long-chain acylcarnitines. Urine organicacids showed dicarboxylic aciduria. Fatty acid oxidationstudies showed reduced oleate and myristate oxidation.His acylcarnitine profile normalized after he wasstarted on a medium-chain triglyceride (MCT) low-fatdiet and carnitine supplementation. Low CACT activityon enzyme assay confirmed the diagnosis. He hasresulting profound developmental delay and epilepsy.The sibling was prospectively treated with a low-fatMCT diet and carnitine supplementation. Acylcarnitineprofile at birth also showed elevated long-chain acylcarnitines. Fatty acid oxidation studies confirmed thediagnosis. To date he has normal development and hasnot had any significant periods of hypoglycaemia orhyperammonaemia.