An infant presented with massive hyperchylomicronemia and a severe encephalopathy. MRI showed marked lipid deposition throughout the brain. Despite the normalization of the biochemistry, there was little clinical improvement, and at 18 months of age she has severe developmental delay, a strikingly abnormal MRI. Apolipoprotein C-II, the lipoprotein on chylomicrons responsible for the activation of lipoprotein lipase, was not detectable in blood. Analysis of the APO C-II gene revealed a novel homozygous point mutation, 1118C→A. Subsequently, another sibling has been born with the same homozygous mutation and similar biochemistry but, perhaps because of early treatment, a normal neurological outcome.
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