SLC25A4 (ANT1 and AAC1) gene mutations cause an intriguing spectrum of human disease, with dominant mutations first reported in adults with progressive external ophthalmoplegia (PEO),1 whereas recessive loss-of-function mutations cause cardiomyopathy and skeletal myopathy.2,3 Furthermore, SLC25A4 de novo dominant mutations can present in neonates with lactic acidosis, severe hypotonia, and respiratory failure.4 Here, we report a patient who presented at age 2 years with mild weakness and hypotonia and was found to have a novel de novo heterozygous SLC25A4 variant (c.97A>T;p.Lys33Gln). This evidence concerns the gene SLC25A4 and lactic acidosis.