A critical study of network models for neural networks and their dynamics.

We use three network models, Erdos-Rényi, Watts-Strogatz and structured nodes, to generate networks sharing several topological features with the neural network of C. elegans (our target network). A new topological measurement, incoming and outgoing edges heat maps, is introduced and used to compare the considered networks. We run these networks as random recurrent neural networks and study their dynamics. We find out that none of the considered network models generates networks similar to the target one both in their topological features and dynamics. Moreover, we find that the dynamics of the target network are very robust to the rewiring of its edges.

HLA class I genotypes in Leber's hereditary optic neuropathy.

There is evidence that mitochondrial DNA (mtDNA) encoded peptides can restrict the immune response in rodents and that these peptides are presented by classical and 'neoclassical' class I major histocompatibility complex (MHC) molecules. We investigated the frequency of HLA-A and two HLA-B genotypes in index cases of 77 families with Leber's hereditary optic neuropathy (LHON), on the basis that there may be an autoimmune component to this disease. There was no association between LHON and any genotype. We conclude that the classical class I MHC loci are not major determinants of the development of blindness in LHON.

Pedigree analysis in Leber hereditary optic neuropathy families with a pathogenic mtDNA mutation.

Eighty-nine index patients from 85 families were defined as having Leber hereditary optic neuropathy (LHON) by the presence of one of the mtDNA mutations at positions 11778 (66 families), 3460 (8 families), or 14484 (11 families). There were 62 secondary cases. Overall, 64% of index cases had a history of similarly affected relatives. The ratios of affected males to affected females were 3.7:1 (11778), 4.3:1 (3460), and 7.7:1 (14484). The 95th centile for age at onset of symptoms was close to 50 years in index, secondary, male, and female patients. There were no differences in the distributions of age at onset between different mutation groups, between index and secondary cases, or between males and females, apart from this being slightly later in all female patients than in male 11778 patients. There was no significant correlation between age at onset in index cases and that in their affected siblings or cousins. Heteroplasmy (< 96% mutant mtDNA) was detected in 4% of affected subjects (67%-90% mutant mtDNA) and in 13.6% of 140 unaffected relatives (< 5%-90% mutant mtDNA). Analysis of all pedigrees, excluding sibships < 50 years of age and index cases, indicated recurrence risks of 30%, 8%, 46%, 10%, 31%, and 6%, respectively, to the brothers, sisters, nephews, nieces, and male and female matrilineal first cousins of index cases. Affected females were more likely to have affected children, particularly daughters, than were unaffected female carriers. The pedigree data were entirely compatible with the previously proposed X-linked susceptibility locus, with a gene frequency of .08, penetrance of .11 in heterozygous females, and 40% of affected females being homozygous, the remainder being explained by heterozygosity and disadvantageous X inactivation.

Antibodies to human optic nerve in Leber's hereditary optic neuropathy.

Mutations of mitochondrial DNA have now been identified in the majority of patients with Leber's hereditary optic neuropathy (LHON). However, these mutations do not explain all the clinical features of LHON, and other pathogenetic factors are likely to be operating. We have analysed serum from 69 LHON patients and their relatives, 58 controls and 14 patients with ischemic or compressive optic neuropathy. A significant proportion of LHON patients had circulating antibodies to tubulin protein. This finding supports the theory that autoimmunity may play some role in the pathogenesis of LHON.

The clinical features of Leber's hereditary optic neuropathy defined by the presence of a pathogenic mitochondrial DNA mutation.

One hundred and seven patients from 79 families were defined as having Leber's hereditary optic neuropathy (LHON) by the presence of one of the mitochondrial DNA (mtDNA) mutations at positions 11778 (60 families), 3460 (seven families) or 14484 (12 families). Only half of the 11778 index patients had a history of similarly affected relatives; this proportion was higher with the 3460 (71%) and 14484 (100%) mutations. The ratios of affected male to female patients were 2.5:1 (11778), 2:1 (3460), and 5.7:1 (14484). Detailed clinical data were available for 79 patients from 55 families. Visual loss developed between the ages of 11 and 30 years in 69%, with a range of 6-62 years, and no significant differences between mutation groups or males and females. It was bilateral in all but two patients, to a median of counting fingers with a central scotoma, developing simultaneously in 22% and sequentially in 78%, with a median inter-eye delay of 8 weeks, and progressing in each eye over a period of 4-6 weeks. Nineteen patients had pain in an affected eye or on eye movements, and four experienced Uhthoff's phenomenon. Retinal microangiopathy was uncommon after 6 months from onset and was not detected in 36% of patients examined within 3 months of visual loss; the microangiopathy was particularly uncommon in the 14484 group. There was no difference in the overall visual outcome between the 11778 and 3460 groups with median final visual acuities of 1/60 and 3/60, respectively. Particularly severe visual loss occurred in one-third of women with the 11778 mutation, to vague perception of light or no perception of light in at least one eye. A multiple sclerosis-like illness was observed in 45% of females with the 11778 mutation. Prognosis was substantially better in the 14484 patients, with recovery to a final visual acuity of at least 6/24, in 71% of patients. Good visual outcome was strongly correlated with age at onset, all those with onset before 20 years having a final visual acuity better than 6/24 as opposed to only 2 out of 6 with later onset. Improvement in vision occurred as long as 4 years after onset. High alcohol and tobacco consumption, cranial or ocular trauma, young or old age at presentation, co-existing neurological disease, and recent childbirth with post-partum haemorrhage, all contributed to diagnostic difficulties in this series, usually in the absence of a family history. These problems were resolved by mtDNA analysis.

Bilateral simultaneous optic neuropathy in adults: clinical, imaging, serological, and genetic studies.

To elucidate the cause(s) of acute or subacute bilateral simultaneous optic neuropathy (BSON) in adult life, a follow up study of 23 patients was performed with clinical assessment, brain MRI, HLA typing, and mitochondrial DNA analysis. The results of CSF electrophoresis were available from previous investigations in 11 patients. At follow up, five (22%) had developed clinically definite multiple sclerosis, four (17%) had mitochondrial DNA point mutations indicating a diagnosis of Leber's hereditary optic neuropathy (LHON). The remaining 14 patients (61%) still had clinically isolated BSON a mean of 50 months after the onset of visual symptoms: three of 14 (21%) had multiple MRI white matter lesions compatible with multiple sclerosis, three of 14 (21%) had the multiple sclerosis associated HLA-DR15/DQw6 haplotype, and one of seven tested had CSF oligoclonal IgG bands; in total only five (36%) had one or more of these risk factors. The low frequency of risk factors for the development of multiple sclerosis in these 14 patients suggests that few will develop multiple sclerosis with more prolonged follow up. It is concluded that: (a) about 20% of cases of BSON without affected relatives are due to LHON; (b) multiple sclerosis develops after BSON in at least 20% of cases, but the long term conversion rate is likely to be considerably less than the rate of over 70% seen after an episode of acute unilateral optic neuritis in adult life.

Mitochondrial DNA diseases: genotype and phenotype in Leber's hereditary optic neuropathy.

We have investigated 107 patients from 79 families with Leber's hereditary optic neuropathy (LHON), defined by the presence of one of the mitochondrial DNA (mtDNA) mutations at positions 11778 (60 families), 3460 (7), or 14484 (12). Only about 60% of the index patients had a history of similarly affected relatives. The ratios of affected male:female patients were 2.5:1 (11778), 2:1 (3460), and 5.7:1 (14484). Visual loss developed between the ages of 11 and 30 years in 69% with a range of 6-62 years, and this was not significantly different between mutation groups or males and females. Retinal microangiopathy was not detected in 36% of patients examined within 3 months of visual loss. A multiple sclerosis-like illness occurred in 45% of females with the 11778 mutation. Prognosis was better in the 14484 than the 3460 or 11778 patients, with useful recovery in 71% of patients. Good visual outcome was positively correlated with early age of onset (before 20 years). Unusual presentations, including young or old age at onset, caused diagnostic difficulties in this series, usually in the absence of a family history, which were resolved by mtDNA analysis. Recurrence risks to relatives could be derived from this series of families with genetically defined LHON.

HLA class II genotypes in Leber's hereditary optic neuropathy.

There is an association between Leber's hereditary optic neuropathy (LHON) and a multiple sclerosis-like illness, raising the possibility of autoimmune pathogenetic mechanisms in LHON. We therefore investigated the frequency of HLA-DR genotypes in members of 79 families with LHON, defined by the presence of a pathogenic mitochondrial DNA mutation. There was no association between LHON and any HLA-DR genotype. Furthermore, affected relative pairs did not share HLA genotypes more than discordant pairs. We conclude that the HLA-DR locus is not a major genetic determinant for the development of blindness in LHON.

Leber's hereditary optic neuropathy mitochondrial DNA mutations in multiple sclerosis.

The observation of a multiple sclerosis (MS)-like illness in patients, particularly women, who carry the most common Leber's hereditary optic neuropathy mitochondrial DNA (mtDNA) mutation may indicate a contributory role for mitochondrial genes in genetic susceptibility to MS. We screened 307 unrelated MS patients, ascertained from population surveys, for the pathogenic Leber's hereditary optic neuropathy mutations at positions 11778 and 3460 of mtDNA, and also studied 20 patients with prominent and early optic nerve involvement. In addition, these 307 patients and 129 control subjects were investigated for the base change at position 13708, which has been suggested to play a role in the pathogenesis of Leber's hereditary optic neuropathy. Neither of the pathogenic mtDNA mutations occurred in the unselected MS patients. The 13708 base change was present in MS patients at a frequency similar to that in healthy control subjects. Three of the patients selected on the basis of severe optic nerve involvement had either the 11778 (one) or 3460 (two) mutations associated with Leber's hereditary optic neuropathy. All were women and none had affected relatives. We conclude that these mutations do not contribute to genetically determined susceptibility in typical MS patients, although a mitochondrial genetic component in the etiology of MS remains possible. A subgroup of MS patients, particularly females with severe bilateral visual failure due to optic neuropathy, may harbor a Leber's hereditary optic neuropathy mutation and we suggest that mtDNA analysis is appropriate in these patients.

Platelet mitochondrial function in Leber's hereditary optic neuropathy.

We report the effect of the 11,778 and 3460 base pair mitochondrial DNA mutations, found in Leber's hereditary optic neuropathy (LHON), on platelet mitochondrial respiratory chain enzyme activity. We measured respiratory chain enzyme activities in platelets from 4 patients with the 3460 mutation, 17 patients with the 11,778 mutation and compared them with those of 41 healthy age-matched controls. We observed a 67% (P < 0.001) reduction in the mean NADH CoQ1 reductase (complex I) activity of the 3460 group compared to the control group. It has been shown previously that platelet mitochondrial biochemistry is affected by cigarette smoking. A significant reduction (25%, P < 0.03) in the mean complex I activity of the 11,778 group was only observed when the non-smokers within that group were compared to the non-smoking controls. The effect of smoking observed in this study may explain why previous workers have not observed a decrease in complex I activity associated with the 11,778 mutation. There was no significant change in the activity of complexes II/III or IV with either of these mutations. There was a significant increase (26%, P < 0.008) in citrate synthase (CS) activity with the non-smoking 11,778 group compared to the non-smoking control group, rising to 40% (P < 0.002) in those with this mutation who smoked. This reflects an increase in mitochondrial mass with the 11,778 mutation. This effect was not observed with the 3460 mutation even though the complex deficiency was much more severe.

Smoking and mitochondrial function: a model for environmental toxins.

Defects of the human mitochondrial respiratory chain have been associated with several diseases including, most recently, certain neurodegenerative disorders. Several studies have used platelet mitochondrial function as a means to determine the potential contribution of respiratory chain defects to the pathogenesis of Parkinson's disease. Platelet biochemistry is subject to modulation by numerous factors that may circulate in the blood, including environmental agents, some of which may be relevant to mitochondrial dysfunction and neuronal toxicity. We measured mitochondrial respiratory chain enzyme activities in platelets from 18 normal healthy non-smoking controls and compared them with those from 23 similarly healthy cigarette smoking individuals. A 24% decrease (p < 0.02) was observed in the mean NADH CoQ1 reductase (complex I) activity of the smoking group compared with that of the non-smoking group. There was no significant change in the activity of any of the other respiratory chain enzymes. This is the first demonstration in vivo of mitochondrial inhibition by a common environmental agent. The results offer a novel mechanism of action for the cellular toxicity, or even mutagenicity, associated with cigarette smoking. In addition, these data have important implications for the interpretation of platelet mitochondrial complex I activities in disease states. They are particularly relevant to our interpretation and understanding of the complex I deficiency in Parkinson's disease platelets.