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The previously unrecognised association of myoclonus in two patients with LHON with the 11778/ND4 pathogenic mutation is described. EEG failed to disclose epileptic figures, and a back averaging study suggested that myoclonus was cortical in origin in both patients.

The pathogenic role of `secondary' mitochondrial DNA (mtDNA) point mutations, when occurring in patients with Leber's hereditary optic neuropathy (LHON) in association with `primary' mutations, is still controversial. We used phosphorus magnetic resonance spectroscopy to establish whether two of these `secondary' LHON mtDNA mutations, 4216/ND1 and 13708/ND5 (haplogroup J), further affect in vivo mitochondrial oxidative metabolism in subjects with the `primary' 11778/ND4 mtDNA mutation. Brain and skeletal muscle energy metabolism was assessed in 10 subjects homoplasmic for the 11778/ND4 mtDNA mutation and 10 subjects homoplasmic for the same mutation occurring on the haplogroup J mtDNA background. Brain phosphocreatine concentration and phosphorylation potential were significantly reduced and brain inorganic phosphate concentration was significantly increased compared with controls in both groups of 11778/ND4-positive subjects. The degree of reduction in the phosphocreatine concentration and phosphorylation potential and of increase in the inorganic phosphate concentration was, however, similar in the two groups with the 11778/ND4 mtDNA mutation with or without the haplogroup J. Similarly, the rate of muscle phosphocreatine resynthesis after exercise, a sensitive index of the rate of mitochondrial ATP production, was reduced by the same extent in both groups of LHON subjects. This in vivo study does not support synergism of the 4216/ND1 and 13708/ND5 `secondary' mutations with the 11778/ND4 `primary' mutation in determining the deficit of energy metabolism in LHON.

We investigated the biochemical phenotype of the mtDNA T8993G point mutation in the ATPase 6 gene, associated with neurogenic muscle weakness, ataxia, and retinitis pigmentosa (NARP), in three patients from two unrelated families. All three carried >80% mutant genome in platelets and were manifesting clinically various degrees of the NARP phenotype. Coupled submitochondrial particles prepared from platelets capable of succinate-sustained ATP synthesis were studied using very sensitive and rapid luminometric and fluorescence methods. A sharp decrease (>95%) in the succinate-sustained ATP synthesis rate of the particles was found, but both the ATP hydrolysis rate and ATP-driven proton translocation (when the protons flow from the matrix to the cytosol) were minimally affected. The T8993G mutation changes the highly conserved residue Leu(156) to Arg in the ATPase 6 subunit (subunit a). This subunit, together with subunit c, is thought to cooperatively catalyze proton translocation and rotate, one with respect to the other, during the catalytic cycle of the F(1)F(0) complex. Our results suggest that the T8993G mutation induces a structural defect in human F(1)F(0)-ATPase that causes a severe impairment of ATP synthesis. This is possibly due to a defect in either the vectorial proton transport from the cytosol to the mitochondrial matrix or the coupling of proton flow through F(0) to ATP synthesis in F(1). Whatever mechanism is involved, this leads to impaired ATP synthesis. On the other hand, ATP hydrolysis that involves proton flow from the matrix to the cytosol is essentially unaffected.

The release through silicone rubber membranes of benzocaine suspended in carbomer hydrogels containing different concentrations of low molecular weight polyols (ethylene glycol, propylene glycol, glycerol, and sorbitol) was studied to establish general principles and procedures for control of the effects on percutaneous absorption caused by changes in drug solubility and/or diffusivity in the vehicle. The effect of the additives on the release is expressed in terms of the relative released amount, i.e., the ratio, Q/Qw, of the amount of drug released from each additive-containing gel to the amount released at the same time from the additive-free gel. The experimental Q/Qwvalues are correlated with values calculated by a simple equation involving known or readily measurable parameters such as the drug concentration in the gel, the drug solubility in the pure liquid phase, and the viscosity of this phase. Derivation of such a relationship from a known equation describing the vehicle-controlled release of suspended drugs was possible because an inverse proportionality was observed between drug diffusivity in the gels and the viscosity of the respective solvents. This relationship is interpreted with respect to current theories on drug diffusion in diluted gels.

The nicotinamide nucleotide dimers (NAD)2 and (NADP)2, obtained by electrochemical reduction of NAD+ and NADP+, are able to reduce such single-electron acceptors as the proteins cytochrome c, azurin and methaemoglobin, though at different rates. Under the same conditions the reduced nicotinamide coenzymes NADH and NADPH are not able to reduce these proteins at measurable rates unless a catalyst (phenazine methosulphate or NADH-cytochrome c reductase in the case of cytochrome) is present. The redox mechanism seems to involve the formation of an NAD(P). radical that in the presence of O2 gives rise to superoxide (O2.-), since superoxide dismutase inhibited these reactions.

Horseradish peroxidase catalyses the oxidation of NAD dimers, (NAD)2, to NAD+ in accordance with a reaction that is pH-dependent and requires 1 mol of O2 per 2 mol of (NAD)2. Horseradish peroxidase also catalyses the peroxidation of (NAD)2 to NAD+. In contrast, bacterial NADH peroxidase does not catalyse the peroxidation or the oxidation of (NAD)2. A free-radical mechanism is proposed for both horseradish-peroxidase-catalysed oxidation and peroxidation of (NAD)2.

ObjectiveTo determine whether a multisystemic bioenergetic deficit is an underlying feature of familial hypobetalipoproteinaemia. MethodsBrain and skeletal muscle bioenergetics were studied by in vivo phosphorus MR spectroscopy (³¹P-MRS) in two neurologically affected members (mother and son) and in one asymptomatic member (daughter) of a kindred with familial hypobetalipoproteinaemia. Plasma concentrations of vitamin E and coenzyme Q₁₀ (CoQ₁₀) were also assessed. ResultsBrain ³¹P-MRS disclosed in all patients a reduced phosphocreatine (PCr) concentration whereas the calculated ADP concentration was increased. Brain phosphorylation potential was reduced in the members by about 40%. Skeletal muscle was studied at rest in the three members and during aerobic exercise and recovery in the son and daughter. Only the mother showed an impaired mitochondrial function at rest. Both son and daughter showed an increased end exercise ADP concentration whereas the rates of postexercise recovery of PCr and ADP were slow in the daughter. The rate of inorganic phosphate recovery was reduced in both cases. Plasma concentration of vitamin E and CoQ₁₀ was below the normal range in all members.ConclusionsStructural changes in mitochondrial membranes and deficit of vitamin E together with reduced availability of CoQ₁₀ can be responsible for the multisystemic bioenergetic deficit. Present findings suggest that CoQ₁₀ supplementation may be important in familial hypobetalipoproteinaemia.

The authors identified two novel heterozygous missense transitions in the gene for the mitochondrial polymerase gammaA subunit (POLG) in a family with an autosomal recessive syndrome comprising progressive external ophthalmoplegia (PEO), polyneuropathy, ataxia, sensorineural hearing loss, and affective disorders. These mutations were not detected in 120 healthy control subjects.

Occipital lobe and calf muscle energy metabolism were studied in vivo by magnetic resonance spectroscopy (³¹P-MRS) in four members of a family harbouring the mitochondrial DNA G3460A mutation causing Leber's hereditary optic neuropathy (LHON). Three siblings carried 100% mutated mitochondrial DNA (homoplasmy), while their mother had coexistence of mutated and wild-type mitochondrial DNA (heteroplasmy). Indices of brain energy metabolism on ³¹P-MRS were abnormal in all subjects examined, but the muscle oxidative phosphorylation rate was normal. These findings indicate a tissue specific distribution of the biochemical expression of the G3460A LHON mutation and suggest that extramitochondrial factors, such as nuclear genes, may influence expression of this mutation in vivo.