MDH2 is a nuclear gene located between HIP1 and YWHAG, and encodes the mitochondrial malate dehydrogenase (MDH) protein, which is essential for the conversion of malate to oxaloacetate as part of the proper functioning of the Krebs cycle.19,20 Ait-El-Mkadem et al reported bi-allelic pathogenic mutations in MDH2 in three unrelated subjects presenting with drug-resistant epilepsy and psychomotor delay.20 Functional studies in fibroblasts from patients showed a loss of MDH2 protein levels and almost undetectable MDH2 enzymatic activity.20 This evidence concerns the gene HIP1 and epilepsy.