[A case of neonatal Mitochondrial DNA depletion syndrome type 13 caused by FBXL4 gene mutation].

Objective: To explore the clinical phenotypes and genetic variant in a neonatal case of Mitochondrial DNA depletion syndrome type 13 (MTDPS13).

Methods: Clinical data and results of genetic testing of a neonate admitted to the Children's Hospital of Zhejiang University School of Medicine in January 2023 was retrospectively analyzed. The study was approved by the Medical Ethics Committee of the Children's Hospital of Zhejiang University.

Results: The male infant was admitted to the NICU due to tachypnea and persistent lactic acidosis 6 hours after birth. At admission, distinctive facial features were noted. Laboratory tests showed elevated lactic acid (< 30 mmol/L). Whole-exome sequencing revealed that he has harbored homozygous c.141del frameshift mutation of FBXL4 gene, which was unreported previously. The mutation was inherited from both of his parents and classified as likely pathogenic based on the guidelines from the American College of Medical Genetics and Genomics (ACMG).

Conclusion: The clinical phenotypes of this case of MTDPS13 is characterized by lactic acidosis, distinctive facial features, growth retardation and developmental delay, for which the homozygous c.141del variant of the FBXL4 gene may be accountable.