A 6 month-old male infant presents with failure to thrive. His mother notes that he has loose, foul smelling stools. A representative field of his blood smear is shown here.

What is the diagnosis?

A. Autoimmune hemolytic anemia
B. Sickle cell anemia
C. Abetalipoproteinemia
D. Microangiopathic hemolytic anemia
E. Glucose-6-phosphate dehydrogenase deficiency

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The diagnosis in this case is abetalipoproteinemia, a rare hereditary disorder in which patients lack apoliporoteins B-48 and B-100, resulting in a decreased ability to absorb dietary fat and fat-soluble vitamins.  Signs of the disorder appear in infancy, usually with failure to thrive and diarrhea. Acanthocytes (red cells with long, spiky projections) are usually seen in the blood, and are caused by an abnormal distribution of membrane lipids in the red blood cell. Later in life, the disease affects the nervous system, and patients may develop ataxia and decreased vision. Treatment involves dietary restriction of triglycerides and supplementation with large doses of fat-soluble vitamins, especially vitamin E.

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