Abstract
BACKGROUND: β-Ureidopropionase deficiency is a rare autosomal recessive disease affecting the last step of pyrimidine degradation. Mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes (MELAS) syndrome is a rare inherited disorder caused by genetic defects in mitochondrial DNA. CASE PRESENTATION: One 8-year-old boy presented with dizziness, vomiting, and convulsions. The gas chromatography-mass spectrometry results suggested β-ureidopropionase deficiency. The whole-exome sequencing results revealed homozygous missense variant c.977G>A (p.R326Q) in UPB1. However, the patient presented with persistent hyperlactacidemia and metabolic acidosis, which did not correspond to the classic features of β-ureidopropionase deficiency. Combined with the manifestations of developmental delay, poor academic performance, and poor sports stamina, whole-mitochondrial-genome sequencing was performed. The results exhibited the variant m.3243A>G of MT-TL1 gene. The level of heterogeneity was 65% in the patient and 17.8% in his mother. Eventually, the final diagnosis of β-ureidopropionase deficiency combined with MELAS syndrome was made. CONCLUSION: The report about β-ureidopropionase deficiency caused by a nuclear gene variant and MELAS syndrome caused by a mitochondrial gene variant coexisting in the same patient enriches the clinical study of these two rare diseases.