Mitochondrial respiratory chain complex I deficiency causes intractable gastrointestinal symptoms

We report the case of a 13‐month‐old girl with frequent vomiting, intractable diarrhea, hyperlactatemia, and liver dysfunction. Although the symptoms were treatment resistant, enteral nutrition formula containing medium‐chain triglycerides reduced the weight loss, vomiting, and diarrhea. Immunostaining of mitochondrial respiratory chain (MRC) complexes of the colonic mucosa confirmed the diagnosis of MRC complex I deficiency. This case shows that this disease should be included in the differential diagnosis of hyperlactatemia and intractable, cryptogenic gastrointestinal symptoms. In addition, the mucosa of the affected gastrointestinal organ should be analyzed on immunostaining or electron microscopy for MRC complexes.