UC Irvine

With the onset of clinical whole exome sequencing, novel gene mutations have been identified in numerous patients with previously undiagnosed diseases, including those with mitochondrial disease of unknown etiology. Complex I deficiency is one of the most common mitochondrial disorders and is both clinically and genetically heterogeneous. Many mutations within the nuclear and mitochondrial genomes have been thoroughly studied for their impact on complex I function based on deleterious alterations in protein function and prevalence among affected individuals. However, many mutations, including splicing mutations, require further analyses of mRNA transcripts in order to understand the impact on disease pathology and potential phenotypic differences.

This study was designed to assess the potential affect of alternative splicing among three patients (two siblings and one unrelated patient) with complex I deficiency and compound heterozygous mutations in NUBPL. Each of them share the same branch-site mutation in NUBPL, c.815-27T>C, but have differences in disease severity. Using primers designed to separately encompass this mutation as well as a different splice mutation in the unrelated patient (c.693+1 G>A), reverse transcription polymerase chain reaction (RT-PCR) was performed on RNA from patient fibroblasts. Gel electrophoresis demonstrated alternative splicing occurring in all three patients following RT-PCR with the branch site mutation primers. In addition, whole exome data from the two siblings was re-analyzed and potential modifier genes affecting NUBPL were studied. Our results support the importance of investigating potentially pathogenic mutations using RNA studies given that alternative splicing can significantly impact phenotypic expression across different tissues and different individuals.