Exome sequencing coupled with mRNA analysis identifies NDUFAF6 as a Leigh gene.
We report here the case of a young male who started to show verbal fluency disturbance, clumsiness and gait anomalies at the age of 3.5years and presented bilateral striatal necrosis. Clinically, the diagnosis was compatible with Leigh syndrome but the underlying molecular defect remained elusive even after exome analysis using autosomal/X-linked recessive or de novo models. Dosage of respiratory chain activity on fibroblasts, but not in muscle, underlined a deficit in complex I. Re-analysis of heterozygous probably pathogenic variants, inherited from one healthy parent, identified the p.Ala178Pro in NDUFAF6, a complex I assembly factor. RNA analysis showed an almost mono-allelic expression of the mutated allele in blood and fibroblasts and puromycin treatment on cultured fibroblasts did not lead to the rescue of the maternal allele expression, not supporting the involvement of nonsense-mediated RNA decay mechanism. Complementation assay underlined a recovery of complex I activity after transduction of the wild-type gene. Since the second mutation was not detected and promoter methylation analysis resulted normal, we hypothesized a non-exonic event in the maternal allele affecting a regulatory element that, in conjunction with the paternal mutation, leads to the autosomal recessive disorder and the different allele expression in various tissues. This paper confirms NDUFAF6 as a genuine morbid gene and proposes the coupling of exome sequencing with mRNA analysis as a method useful for enhancing the exome sequencing detection rate when the simple application of classical inheritance models fails.
Medical Genetics, University of Siena, Siena, Italy.
Laura
L
Bianciardi
Medical Genetics, University of Siena, Siena, Italy.
Valentina
V
Imperatore
Mitochondrial Biology Unit, Medical Research Council Cambridge, Cambridge, UK.
Erika
E
Fernandez-Vizarra
Department of Translational Research and New Technologies in Medicine and Surgery, University of Pisa, Pisa, Italy.
Angela
A
Lopomo
Mitochondrial Biology Unit, Medical Research Council Cambridge, Cambridge, UK; Department of Biochemical Sciences, Sapienza University, Rome, Italy.
Micol
M
Falabella
Department of Medical Biotechnologies, University of Siena, Siena, Italy.
Simone
S
Furini
Unit of Diagnostic and Therapeutic Neuroradiology, Department of Neurosciences, Azienda Ospedaliera Universitaria Senese, Siena, Italy.
Paolo
P
Galluzzi
Clinica Pediatrica, University of Siena, Siena, Italy.
Salvatore
S
Grosso
Mitochondrial Biology Unit, Medical Research Council Cambridge, Cambridge, UK.
Massimo
M
Zeviani
Medical Genetics, University of Siena, Siena, Italy; Genetica Medica, Azienda Ospedaliera Universitaria Senese, Siena, Italy. Electronic address: alessandra.renieri@unisi.it.
Alessandra
A
Renieri
Medical Genetics, University of Siena, Siena, Italy; Genetica Medica, Azienda Ospedaliera Universitaria Senese, Siena, Italy. Electronic address: francesca.mari@unisi.it.
Francesca
F
Mari
Medical Genetics, University of Siena, Siena, Italy.
Elisa
E
Frullanti
D000483:Alleles; D002675:Child, Preschool; D059472:Exome / Q000235:genetics*; D006579:Heterozygote; D059014:High-Throughput Nucleotide Sequencing; D006801:Humans; D007888:Leigh Disease / Q000235:genetics* / Q000503:physiopathology; D008297:Male; D024101:Mitochondrial Proteins / Q000235:genetics*; D009154:Mutation; D010375:Pedigree; D010641:Phenotype; D012333:RNA, Messenger / Q000235:genetics; D013064:Speech Disorders / Q000235:genetics* / Q000503:physiopathology; D020955:Striatonigral Degeneration / Q000151:congenital / Q000235:genetics / Q000503:physiopathology
D024101:Mitochondrial Proteins; C530233:NDUFAF6 protein, human; D012333:RNA, Messenger
Exome sequencing; Leigh syndrome; NDUFAF6; RNA analysis