Although symptomatic lipoproteinemias are rare in childhood, early detection often can prevent severe complications. Abetalipoproteinemia is characterized by severe hypolipidemia, fat malabsorption, failure to thrive, unusual spiculated erythrocytes known as acanthocytes, and progressive neuromuscular and retinal pigmentary degeneration believed to be related to vitamin E deficiency. Plasma triglyceride concentrations are so low as to be frequently undetectable, and cholesterol concentrations typically are less than 50% of normal. This disorder results from an inability of both enterocytes and hepatocytes to secrete their apoprotein B-containing lipoproteins. Consequently, chylomicrons, very low-density lipoprotein are absent from plasma. A related disorder, homozygous familial hypobetalipoproteinemia, mimics the signs and symptoms and the characteristic lipid levels of abetalipoproteinemia, but is believed to involve a different mutation.