Targeted exome sequencing for mitochondrial disorders reveals high genetic heterogeneity.
BACKGROUND
Mitochondrial disorders are difficult to diagnose due to extreme genetic and phenotypic heterogeneities.


METHODS
We explored the utility of targeted next-generation sequencing for the diagnosis of mitochondrial disorders in 148 patients submitted for clinical testing. A panel of 447 nuclear genes encoding mitochondrial respiratory chain complexes, and other genes inducing secondary mitochondrial dysfunction or that cause diseases which mimic mitochondrial disorders were tested.


RESULTS
We identified variants considered to be possibly disease-causing based on family segregation data and/or variants already known to cause disease in twelve genes in thirteen patients. Rare or novel variants of unknown significance were identified in 45 additional genes for various metabolic, genetic or neurogenetic disorders.


CONCLUSIONS
Primary mitochondrial defects were confirmed only in four patients indicating that majority of patients with suspected mitochondrial disorders are presumably not the result of direct impairment of energy production. Our results support that clinical and routine laboratory ascertainment for mitochondrial disorders are challenging due to significant overlapping non-specific clinical symptoms and lack of specific biomarkers. While next-generation sequencing shows promise for diagnosing suspected mitochondrial disorders, the challenges remain as the underlying genetic heterogeneity may be greater than suspected and it is further confounded by the similarity of symptoms with other conditions as we report here.
Jeana T
JT
DaRe
Valeria
V
Vasta
John
J
Penn
Nguyen-Thao B
NT
Tran
Seattle Children's Hospital Research Institute, 1900 9th Ave, Seattle, WA 98101, USA. sihahn@uw.edu.
Si Houn
SH
Hahn
D000293:Adolescent; D000328:Adult; D000368:Aged; D002648:Child; D002675:Child, Preschool; D059472:Exome; D018740:Genetic Heterogeneity; D059014:High-Throughput Nucleotide Sequencing; D006801:Humans; D007223:Infant; D008875:Middle Aged; D028361:Mitochondrial Diseases / Q000175:diagnosis* / Q000235:genetics*; D009154:Mutation; D011786:Quality Control; D055815:Young Adult