Ataxia due to abetalipoproteinemia

**Definition:** Ataxia in the setting of abetalipoproteinemia, a rare autosomal recessive disorder caused by a mutation of the MTP gene coding for microsomal triglyceride transfer protein which impairs the ability to produce very low density lipoprotein. All patients have fat malabsorption, acanthocytosis, hypocholesterolemia, and absent apolipoprotein B.