A 10-MONTH-OLD white girl was referred to the University of North Carolina Hospitals for failure to thrive, chronic diarrhea, and a slightly protuberant abdomen. After 3 months of breastfeeding, a commercially available formula (Similac, Ross Products Division, Abbott Laboratories, Columbus, Ohio) was introduced, which resulted in episodes of emesis and large loose stools. At 5 months poor growth had become evident with weight less than the fifth percentile; height in the 25th percentile; and head circumference less than the fifth percentile. At 7 months of age, the patient's diarrhea was severe with voluminous watery green stools devoid of mucus or blood. Her weight continued to decline. A gluten-free diet failed to result in improvement of her condition. Motor development was delayed. Family history was unremarkable.
Peripheral blood smear showed acanthocytes (Figure 1), with a hemoglobin level of 120 g/L and a hematocrit of 0.36. Prothrombin time, partial thromboplastin time,