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Using a quantitative quadruple immunofluorescent assay to diagnose isolated mitochondrial Complex I deficiency.

Using a quantitative quadruple immunofluorescent assay to diagnose isolated mitochondrial Complex I deficiency.
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Ahmed ST, Alston CL, Hopton S, He L, Hargreaves IP, Falkous G, Oláhová M, McFarland R, Turnbull DM, Rocha MC, Taylor RW,


Ahmed ST, Alston CL, Hopton S, He L, Hargreaves IP, Falkous G, Oláhová M, McFarland R, Turnbull DM, Rocha MC, Taylor RW, (click to view)

Ahmed ST, Alston CL, Hopton S, He L, Hargreaves IP, Falkous G, Oláhová M, McFarland R, Turnbull DM, Rocha MC, Taylor RW,

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Scientific reports 2017 11 157(1) 15676 doi 10.1038/s41598-017-14623-2
Abstract

Isolated Complex I (CI) deficiency is the most commonly observed mitochondrial respiratory chain biochemical defect, affecting the largest OXPHOS component. CI is genetically heterogeneous; pathogenic variants affect one of 38 nuclear-encoded subunits, 7 mitochondrial DNA (mtDNA)-encoded subunits or 14 known CI assembly factors. The laboratory diagnosis relies on the spectrophotometric assay of enzyme activity in mitochondrially-enriched tissue homogenates, requiring at least 50 mg skeletal muscle, as there is no reliable histochemical method for assessing CI activity directly in tissue cryosections. We have assessed a validated quadruple immunofluorescent OXPHOS (IHC) assay to detect CI deficiency in the diagnostic setting, using 10 µm transverse muscle sections from 25 patients with genetically-proven pathogenic CI variants. We observed loss of NDUFB8 immunoreactivity in all patients with mutations affecting nuclear-encoding structural subunits and assembly factors, whilst only 3 of the 10 patients with mutations affecting mtDNA-encoded structural subunits showed loss of NDUFB8, confirmed by BN-PAGE analysis of CI assembly and IHC using an alternative, commercially-available CI (NDUFS3) antibody. The IHC assay has clear diagnostic potential to identify patients with a CI defect of Mendelian origins, whilst highlighting the necessity of complete mitochondrial genome sequencing in the diagnostic work-up of patients with suspected mitochondrial disease.

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