Identification of novel NDUFA3 variants in a patient with mitochondrial disorders

Background: Mitochondrial respiratory chain (RC) dysfunction constitutes the biochemical defect underlining a group of heterogenous clinical presentations known as mitochondrial disorders. NDUFA3 is an accessory subunit of Complex I (CI) and has recently been associated with Leigh Syndrome. However, the genetic evidence is limited and no functional analysis is available on the molecular mechanism. Methods: We investigated the clinical features of the second family with biallelic NDUFA3 variants. The patient's cells and HEK293T cells with NDUFA3 knock down (KD) were assessed to study the RC dysfunction. A zebrafish model with the morpholino targeting on ndufa3 were generated to study the phenotypes caused by ndufa3 disruption. Results: The affected boy demonstrated global developmental delay, neurosensory hearing impairment, strabismus, muscle weakness, and hypertonia. He harbored a paternal exonic deletion NC_000019.9:g.54608143_54614387delinsCG and a maternally-inherited missense variant NM_004542.4:c.173G>A; p.(Arg58His). In patient's cells and HEK293T cells with NDUFA3 KD, reduced levels of NDUFA3 and CI and Complex IV (CIV) were observed, which further impaired endogenous respiration and ATP generation. Re-expression of the wild-type but not the mutant NDUFA3 restored the CI and CIV levels in NDUFA3 deficient cells. Zebrafish with ndufa3 disruption demonstrated ndufa3 KD affected locomotor development. Conclusions: Our findings confirm the association between NDUFA3 molecular defects and Leigh syndrome spectrum.