NDUFS6 mutations are a novel cause of lethal neonatal mitochondrial complex I deficiency
Denise M. Kirby, … , Michael T. Ryan, David R. Thorburn
Denise M. Kirby, … , Michael T. Ryan, David R. Thorburn
Published September 15, 2004
Citation Information: J Clin Invest. 2004;114(6):837-845. https://doi.org/10.1172/JCI20683.
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Article Genetics

NDUFS6 mutations are a novel cause of lethal neonatal mitochondrial complex I deficiency

Abstract

Complex I deficiency, the most common respiratory chain defect, is genetically heterogeneous: mutations in 8 nuclear and 7 mitochondrial DNA genes encoding complex I subunits have been described. However, these genes account for disease in only a minority of complex I–deficient patients. We investigated whether there may be an unknown common gene by performing functional complementation analysis of cell lines from 10 unrelated patients. Two of the patients were found to have mitochondrial DNA mutations. The other 8 represented 7 different (nuclear) complementation groups, all but 1 of which showed abnormalities of complex I assembly. It is thus unlikely that any one unknown gene accounts for a large proportion of complex I cases. The 2 patients sharing a nuclear complementation group had a similar abnormal complex I assembly profile and were studied further by homozygosity mapping, chromosome transfers, and microarray expression analysis. NDUFS6, a complex I subunit gene not previously associated with complex I deficiency, was grossly underexpressed in the 2 patient cell lines. Both patients had homozygous mutations in this gene, one causing a splicing abnormality and the other a large deletion. This integrated approach to gene identification offers promise for identifying other unknown causes of respiratory chain disorders.

Authors

Denise M. Kirby, Renato Salemi, Canny Sugiana, Akira Ohtake, Lee Parry, Katrina M. Bell, Edwin P. Kirk, Avihu Boneh, Robert W. Taylor, Hans-Henrik M. Dahl, Michael T. Ryan, David R. Thorburn

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Analysis of NDUFS6 cDNA and genomic DNA in families B and C. (A) Two per...
Analysis of NDUFS6 cDNA and genomic DNA in families B and C. (A) Two percent agarose gel of NDUFS6 cDNA fragments generated by standard PCR. Lanes show control (Co); patient B (B); patient C (C); patient H (H); dH2O blank (Bl). PCR of NDUFS6 cDNA gave no product in patient B and a larger fragment than the control in patient C. (B) A representation depicting the frameshift and creation of a premature stop codon caused by the 26-bp insertion of intronic sequence in the proband from family C (bottom). Translation of the control sequence is also shown for comparison (top). The diagram shows the exon 2/exon 3 boundary, with the inserted sequence shown in bold and underlined and a stop codon represented by an asterisk. (C) 0.8% agarose gel of NDUFS6 fragments generated by long-range PCR using forward and reverse primers located 6.2 kb apart. Lanes 2_5, unrelated complex I_deficient patients. The PCR product in patient B is approximately 4 kb smaller than that of other samples. The approximately 2-kb fragment from lane 6 was sequenced and the deletion breakpoints elucidated. (D) Schematic representation of the 4.175-kb deletion, which encompasses exons 3 and 4 (shaded box) of the 14.5-kb NDUFS6 gene in the proband from family B. The exact homozygous deletion breakpoints are also shown with the immediate sequence before and after each breakpoint included.