Expanding the phenotypic and genetic spectrum of GTPBP3 deficiency: findings from nine Chinese pedigrees.

Background: GTPBP3 catalyzes τm(s) U biosynthesis at the 34th wobble position of mitochondrial tRNAs, the hypomodification of τmU leads to mitochondrial disease. While twenty-three variants of GTPBP3 have been reported worldwide, the genetic landscape in China remains uncertain.

Methods: By using whole-exome sequencing, the candidate individuals carrying GTPBP3 variants were screened and identified. Pathogenicity analysis of variants was biochemically verified by patients-derived immortalized lymphocytes and cell models.

Results: Through whole-exome sequencing, thirteen variants associated with GTPBP3 were identified in nine Chinese pedigrees, with eight of these variants being newly reported. Affected individuals displayed classic neurologic phenotypes and heart complications including developmental delay, seizures, hypotonia, exercise intolerance, and hypertrophic cardiomyopathy. Additionally, they displayed new symptoms such as eye problems like strabismus and heart issues related to valve function. Studies conducted on patient-derived cells provided evidence of reduced levels of GTPBP3 and impairment in mitochondrial energetic biogenesis. Re-expressing GTPBP3 variants in knockout cell lines further defined the pathogenicity of the novel variants. Analysis of the genetic spectrum in the Chinese population highlighted a concentration in exons 4 and 6, with c.689A > C being the prominent hotspot.

Conclusion: Our findings emphasize the extensive clinical and genetic implications of GTPBP3-related mitochondrial disorders, particularly within the Chinese population, but further investigations are needed to explore the phenotype-genotype correlation.