Pyruvate dehydrogenase deficit is one of the forms of severe hereditary mitochondrial metabolic diseases characterized by impaired energy metabolism and manifested by a wide range of neurological symptoms. The difficulty in selecting therapy lies in the insufficient number of data on the management of children with this pathology due to death at an early age and insufficient diagnosis during life. The exact prevalence of the disease is unknown, presumably less than 1 in 1,000,000, which allows it to be attributed to orphan diseases. The article presents a case of observation of a child with a rare neurometabolic disease pyruvate dehydrogenase complex E1 deficiency. The diagnosis was suspected after his birth on the basis of neurological symptoms, neonatal hyperamonemia, hyperlactatemia and confirmed after exome sequencing, where a homozygous variant of the nucleotide sequence in the PDNA1 gene (X-19359612-C-E) was revealed. At the age of 2 months, he began to receive a ketogenic diet - a high–fat, low-carbohydrate dry mixture for enteral nutrition, metabolic therapy, Vit B1 (300 mg /day). The article presents indicators of biochemical blood testing, acid-base state of blood, dynamics of the neurological picture during the period of observation of the patient. Early diagnosis and initiation of therapy is extremely important for the physical and neuropsychiatric development of children with this pathology. Despite the lack of highly effective etiotropic treatment, in some cases an improvement in the clinical course is observed with the use of thiamine preparations, as well as adherence to a ketogenic diet.