Advancing the diagnosis of mitochondrial diseases with trio genome sequencing

Abstract

Background: The molecular diagnosis of patients with childhood onset mitochondrial disease can be challenging and may require invasive diagnostic techniques. Mitochondrial diseases can have any mode of inheritance; the most common pattern in children is autosomal recessive. Genome sequencing (GS) has the advantage of effectively analyzing both mitochondrial and nuclear genes, including coding and non-coding regions. Sequencing family trios enables phasing of variants which is particularly advantageous when an autosomal recessive pattern of inheritance is suspected. Methods: We performed genome sequencing of DNA extracted from blood of 40 pediatric patients with suspected mitochondrial disease and their parents. The sequencing data were interrogated to evaluate the diagnostic utility of trio GS, and where needed, further functional studies were undertaken. Results: To date, 58% of the patients in the cohort have reached a molecular diagnosis. Pathogenic variants were identified in 22 different genes, 83% encoded in the nuclear genome, and 17% in the mtDNA. Cases from this cohort that highlight the utility of trio GS include the identification of variants in known and novel disease genes, a deep intronic variant, and an apparently synonymous variant that creates a splicing defect. Interrogation of trio GS data also allowed analysis of mtDNA inheritance, showing an absence of biparental mitochondrial DNA transmission. Conclusion: Trio GS was useful in identifying variants in both nuclear and mitochondrial genes. Variant prioritization was facilitated by simultaneous segregation. The diagnostic utility was increased by combining trio GS with other molecular techniques such as RNA and cDNA studies.L6351864282021-06-10 <br />