Lysinuric protein intolerance can be misdiagnosed as food protein-induced enterocolitis syndrome

Food protein–induced enterocolitis syndrome (FPIES) is a rising non-IgE-mediated food allergy triggered by specific food proteins (cow's milk, soy, and grains are the common offending foods). FPIES requires total elimination of the offending food from the diet and typically resolves by 3 yr of age. Metabolic disorders, such as lysinuric protein intolerance (LPI), are often underestimated in the differential diagnosis of FPIES. Although rare, these inherited conditions require different and life-long nutrition and dietary intervention to prevent impaired developments in infants. We present the case of an infant with LPI misdiagnosed as FPIES and discuss the similarities and differences between these two conditions.