Table 1

Summary of the clinical, histological, biochemical and genetic data of the patient at 14 and 20 years of age

Age (years)
1420
NR, normal range; MRC, Medical Research Council.
Clinical presentationMRC scale 4/5 for both proximal arm and leg muscles and for foot dorsiflexorsMRC scale 5/5 for both proximal and distal arm and leg muscles, mild difficulty in heelwalking
Exercise intolerance and painful muscle cramps; scapular wingingNo exercise intolerance, no muscle cramps; mild scapular winging
    Somatic growthHeight: 3rd–10th percentile; weight: below 3rd percentileHeight: 50th percentile; weight: 5th percentile
Serum lactate (NR 0.5–2.2 mmol/l)Highly elevated: up to 12.8 mmol/l; abnormal increase after exerciseMildly elevated: 2.9 mmol/l; normal increase after exercise
    ElectromyographyMyopathic changes, polyphasic, low amplitude action potentials in deltoid and quadriceps musclesNormal in deltoid and quadriceps, but very mild increase in spontaneous activity in the right tibialis anterior muscle
    Muscle histologyChronic myopathy; 50% ragged red fibres; severe lipid accumulation; severe COX defect in all fibresMild myopathic changes; 47% ragged red fibres; milder lipid accumulation; 14% COX positive fibres
ImmunohistochemistryVirtual absence of COX II/III but normal staining for COX IV in all fibresCOX positive fibres were positive for COX II/III, IV, and Vab, but some of the COX negative fibres were also positive for COX IV and Vab
COX (NR 0.90–4.70)0.03 U/U CS;0.08 U/U
CS: 45–105 U/gNCP)256 U/g NCP136 U/g NCP
Rate of mutant mtDNA93% mutant mtDNA in muscle; 0% in hair follicles; 0% in blood50% mutant mtDNA in muscle; 0% mutant in myoblasts