Defective mitochondrial adenosine triphosphate production in skeletal muscle from patients with dominant optic atrophy due to OPA1 mutations.
OBJECTIVE
To assess whether impaired energy metabolism in skeletal muscle is a hallmark feature of patients with dominant optic atrophy due to several different mutations in the OPA1 gene.


METHODS
We used phosphorus 31 magnetic resonance spectroscopy to assess calf muscle oxidative metabolism in subjects with molecularly defined dominant optic atrophy carrying different mutations in the OPA1 gene. In a subset of patients, we also evaluated serum lactate levels after exercise and muscle biopsy results for histology and mitochondrial DNA analysis.


METHODS
University neuromuscular and neurogenetics and magnetic resonance imaging units.


METHODS
Eighteen patients with dominant optic atrophy were enrolled from 8 unrelated families, 7 of which carried an OPA1 mutation predicted to induce haploinsufficiency and 1 with a missense mutation in exon 27. Fifteen patients had documented optic atrophy.


METHODS
Presence of skeletal muscle mitochondrial oxidative phosphorylation dysfunction as assessed by phosphorus 31 magnetic resonance spectroscopy, serum lactate levels, and histological and mitochondrial DNA analysis.


RESULTS
Phosphorus 31 magnetic resonance spectroscopy showed reduced phosphorylation potential in the calf muscle at rest in patients with an OPA1 mutation (-24% from normal mean; P = .003) as well as a reduced maximum rate of mitochondrial adenosine triphosphate synthesis (-36%; P < .001; ranging from -28% to -49% in association with different mutations). In 4 of 10 patients (40%), the serum lactate level after exercise was elevated. Only 2 of 5 muscle biopsies, from the 2 patients with a missense mutation, showed slight myopathic changes. Low levels of mitochondrial DNA multiple deletions were found in all muscle biopsies.


CONCLUSIONS
Defective oxidative phosphorylation in skeletal muscle is a subclinical feature of patients with OPA1-related dominant optic atrophy, indicating a systemic expression of the OPA1 defect, similar to that previously reported for Leber hereditary optic neuropathy due to complex I dysfunction. This defect of oxidative phosphorylation does not appear to depend on the low amounts of mitochondrial DNA multiple deletions detected in muscle biopsies.
Lodi
Raffaele
R
MR Spectroscopy Unit, Department of Internal Medicine, Aging, and Nephrology, University of Bologna, Bologna, Italy. raffaele.lodi@unibo.it
Tonon
Caterina
C
Valentino
Maria Lucia
ML
Manners
David
D
Testa
Claudia
C
Malucelli
Emil
E
La Morgia
Chiara
C
Barboni
Piero
P
Carbonelli
Michele
M
Schimpf
Simone
S
Wissinger
Bernd
B
Zeviani
Massimo
M
Baruzzi
Agostino
A
Liguori
Rocco
R
Barbiroli
Bruno
B
Carelli
Valerio
V
D000255:Adenosine Triphosphate / Q000096:biosynthesis / Q000235:genetics*; D000328:Adult; D000368:Aged; D004272:DNA, Mitochondrial / Q000235:genetics* / Q000378:metabolism; D005260:Female; D020558:GTP Phosphohydrolases / Q000235:genetics*; D006801:Humans; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000378:metabolism / Q000473:pathology* / Q000502:physiology; D009154:Mutation / Q000235:genetics*; D020125:Mutation, Missense / Q000235:genetics; D029241:Optic Atrophy, Autosomal Dominant / Q000235:genetics* / Q000378:metabolism; D010085:Oxidative Phosphorylation; D055815:Young Adult
D004272:DNA, Mitochondrial; D000255:Adenosine Triphosphate; D020558:GTP Phosphohydrolases; C415198:OPA1 protein, human