In our case, exome sequencing, where the raw data was filtered for genes previously described in mitochondrial disease, revealed one suspected pathogenic mutation in a mitochondrial gene; a deletion of one nucleotide (c.399delA) causing a frameshift (p.Glu133AspfsTer25) in BCS1L. Since this mutation is predicted to lead to severe protein truncation it was deemed very probably damaging. The gene discussed is BCS1L; the disease is inborn mitochondrial metabolism disorder.