A5814G mutation in mitochondrial DNA can cause mitochondrial myopathy and cardiomyopathy

We describe a 5-year-old child with hypertrophic cardiomyopathy, mitochondrial myopathy, and lactic acidosis. Mitochondrial DNA analysis showed a heteroplasmic A5814G point mutation in the tRNA(Cys) gene. The mutational load was extremely high (>95%) in muscle, fibroblasts, and blood. This report expands the clinical heterogeneity of the A5814G mutation, which should be considered in the differential diagnosis of hypertrophic cardiomyopathy in childhood.

Melatonin treatment enhances the efficiency of mice immunization with Venezuelan equine encephalomyelitis virus TC-83

To determine whether treatment with melatonin (MLT) improves the efficiency of immunization against Venezuelan equine encephalomyelitis (VEE) virus, mice were vaccinated with TC-83 VEE virus and treated daily with MLT (1 or 5 mg/kg) starting 3 days before immunization, until 10 days after. IgM antibody titers were determined at days 7, 14, and 21 post-immunization. IL-10 levels were assayed at day 14 postvaccination. Treatment with MLT increased antibody titers 14 days after the immunization. IL-10 levels also increased with MLT treatment (1 and 5 mg/kg). Mice were challenged with live VEE virus at day 21 postimmunization, and viral titers were plaque assayed in chicken embryo fibroblasts 4 days after the infection. Following this challenge brain virus levels were significantly reduced. The results suggest that MLT treatment enhances the efficiency of mice immunization against VEE virus.

Melatonin prolongs survival of immunodepressed mice infected with the Venezuelan equine encephalomyelitis virus

Male albino mice immunodepressed after the injection of dexamethasone (DEX) were inoculated intraperitoneally with the Guajira strain of Venezuelan equine encephalomyelitis (VEE) virus. Melatonin (MLT) was administered daily, at a dose of 500 micrograms/kg bodyweight, for 3 days before virus inoculation and 10 days after. Serum levels of granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin-2 (IL-2) were determined in all the experimental groups (control, DEX, DEX + MLT, DEX + VEE, DEX + VEE + MLT, VEE and MLT). At day 6 after the virus inoculation, the survival rate was significantly increased from 0% in group DEX + VEE to 32.5% in the group of immunodepressed infected mice treated with MLT (DEX + VEE + MLT). By day 10 a survival rate of 10% was found in group DEX + VEE + MLT and 0% in group VEE. No alterations in IL-2 serum levels were observed. MLT increased GM-CSF in control and in DEX-treated mice. In the VEE virus-infected mice treated with DEX, serum levels of GM-CSF increased progressively from day 1 to 5 postinoculation. In contrast, the levels of GM-CSF in infected immunodepressed mice treated with MLT decreased significantly from day 1 to 5 postinoculation. At day 5 after viral inoculation, no differences were detected in the cerebral viral titres in groups VEE, DEX + VEE and DEX + MLT + VEE. These results show that MLT does not inhibit VEE viral replication in the brain of immunodepressed mice.

High intensity light increases olfactory bulb melatonin in Venezuelan equine encephalitis virus infection

In mice infected with the Venezuelan equine encephalomyelitis (VEE) virus and exposed to high intensity light (2500 lux) with a 12 h light: 12 h dark photoperiod, a significant increase in the levels of melatonin in the olfactory bulb was observed. The significance of these findings deserves further studies to understand the mechanisms involved in this effect since the olfactory bulbs have been proposed as first portal for VEE virus entry into the CNS. The increase in melatonin content could represent one of the mechanisms of defense against the viral attack.

Recurrent myoglobinuria due to a nonsense mutation in the COX I gene of mitochondrial DNA

OBJECTIVE

To elucidate the molecular basis of a mitochondrial myopathy associated with recurrent myoglobinuria and cytochrome c oxidase (COX) deficiency in muscle.

BACKGROUND

Recurrent myoglobinuria is typically seen in patients with inborn errors of carbohydrate or lipid metabolism, the main sources of energy for muscle contraction. Relatively little attention has been directed to defects of the mitochondrial respiratory chain in patients with otherwise unexplained recurrent myoglobinuria.

METHODS

Having documented COX deficiency histochemically and biochemically in the muscle biopsy from a patient with exercise-induced recurrent myoglobinuria, the authors sequenced the three mitochondrial DNA (mtDNA)-encoded COX genes, and performed restriction fragment length polymorphism analysis and single-fiber PCR.

RESULTS

The authors identified a nonsense mutation (G5920A) in the COX I gene in muscle mtDNA. The mutation was heteroplasmic and abundantly present in COX-negative fibers, but less abundant or absent in COX-positive fibers; it was not found in blood or fibroblasts from the patient or in blood samples from the patient's asymptomatic mother and sister.

CONCLUSIONS

The G5920A mutation caused COX deficiency in muscle, explaining the exercise intolerance and the low muscle capacity for oxidative phosphorylation documented by cycle ergometry. The sporadic occurrence of this mutation in muscle alone suggests that it arose de novo in myogenic stem cells after germ-layer differentiation. Mutations in mtDNA-encoded COX genes should be considered in patients with recurrent myoglobinuria.

Kearns-sayre syndrome: oncocytic transformation of choroid plexus epithelium

Kearns-Sayre syndrome (KSS) is a sporadic multisystem disorder due to a defect of oxidative phosphorylation and associated with clonally-expanded rearrangements of mitochondrial DNA (mtDNA) deletions (Delta-mtDNAs) and/or duplications (dup-mtDNAs). To gain further insight into the pathogenesis of CNS dysfunction in KSS, we studied the choroid plexus from two autoptic cases using in situ hybridization (ISH) of mtDNA, and immunohistochemistry to detect mtDNA and nuclear DNA-encoded subunits of the respiratory chain. Neuropathological examination of both cases showed oncocytic transformation of choroid plexus epithelial cells. In the same cells, ISH demonstrated that the predominant species of mtDNA were Delta-mtDNAs, and immunohistochemistry showed a decreased expression of mtDNA-encoded proteins. We suggest that mitochondrial abnormalities due to the presence of abundant Delta-mtDNAs in the choroid plexus play an important role in causing the increased cerebrospinal fluid (CSF) protein and reduced folic-acid levels that are characteristic of KSS.

Computerized brain tomography in patients with Schizophrenia

We carried out brain tomography of 27 patients with schizophrenia and 17 normal control subjects. DSM-IV criteria were used for diagnosis. The parameters studied were: brain volume, lateral and third ventricles, brain surface and brain indexes. Previously the patients were evaluated with the following clinical scales: Positive and Negative Syndrome Scale (PANSS), Brief Psychiatric Rating Scale (BPRS), Global Assessment of Functioning Scale (GAF) and the GRAFFAR scale to evaluate cultural and socioeconomical levels. We detected an increase in the right and left lateral ventricles: brain ratios, an increase in the width of Sylvian fissures and in the third ventricle index. We did not find differences that could be related to sex or to a familial history of mental disease. No differences were observed in the group receiving medication when compared with the group of untreated patients.

Primary LAMP-2 deficiency causes X-linked vacuolar cardiomyopathy and myopathy (Danon disease)

"Lysosomal glycogen storage disease with normal acid maltase" which was originally described by Danon et al., is characterized clinically by cardiomyopathy, myopathy and variable mental retardation. The pathological hallmark of the disease is intracytoplasmic vacuoles containing autophagic material and glycogen in skeletal and cardiac muscle cells. Sarcolemmal proteins and basal lamina are associated with the vacuolar membranes. Here we report ten unrelated patients, including one of the patients from the original case report, who have primary deficiencies of LAMP-2, a principal lysosomal membrane protein. From these results and the finding that LAMP-2-deficient mice manifest a similar vacuolar cardioskeletal myopathy, we conclude that primary LAMP-2 deficiency is the cause of Danon disease. To our knowledge this is the first example of human cardiopathy-myopathy that is caused by mutations in a lysosomal structural protein rather than an enzymatic protein.

[Huntington disease. A review]

Huntington's disease (HD) is a hereditary autosomal dominant neurodegenerative disease characterized by motor, cognitive and psychiatric symptoms. It affects about 1 in 10,000 individuals. The onset of symptoms typically occurs in the third or fourth decade of life, though it may appear at any age. The molecular basis of the disease is the expansion of the trinucleotide CAG in the first exon of a gene on chromosome four (4p 16.3). This gene encodes the protein huntingtin of 3136 amino acids. The mutation of huntingtin produces an expanded stretch of glutamine (Gln) residues. This CAG/polyGln expansion has 6 to 39 units in normal individuals and 36 to 180 units in HD patients. The normal function of huntingtin and the pathogenic mechanisms caused by the expanded polyGln of mutant huntingtin remain incompletely characterized. Huntingtin appears to be associated with synaptic vesicles and/or microtubules and seems to have an important role in vesicular transport and/or the binding to the cytoskeleton. It is thought that this protein is important in embryogenesis and that its mutant form alters the function of the mitochondrial respiratory chain. The toxic gain of function caused by huntingtin could either be an overactivity of the normal function or the introduction of a novel function. Its interactions with other proteins could lead to an impairment of the cellular function or to its own polymerization to form insoluble aggregates. The intraneuronal aggregates could affect gene transcription, protein interactions, protein transport inside the nucleus and cytoplasm, and the vesicular transport. However, since a dissociation between the aggregation of huntingtin and the selective pattern of striatal neuronal loss has been demonstrated, it is believed that other properties of the mutant huntingtin, like proteolysis and the interactions with other proteins that affect vesicular trafficking and nuclear transport, could be responsible for the neurodegeneration. On gross examination, 80% of HD brains show atrophy of the frontal lobes. A bilateral, symmetric atrophy of the striatum is observed in 95% of the HD brains. The mean brain weight in HD patients is approximately 30% lower than in normal individuals. Striatal degeneration has an ordered and topographic distribution. The tail of the caudate nucleus shows more degeneration than the head. The caudate atrophy is associated to a gradual atrophy and neuronal loss in other brain regions as the disease progresses. The striatal and cerebral cortex projection neurons are much more susceptible to the disease than interneurons. In the neostriatum, the levels of GABA, dynorphin and substance P are decreased, but the concentrations of somatostatin and neuropeptide Y increase. An impairment of energy metabolism in HD and a sensitivity to oxidative stress and to the cytotoxic effects of glutamate seem to contribute to the neuronal death in HD. It is proposed that melatonin should be assayed in cell cultures and in transgenic animals due to its potent antioxidant and free radical scavenger properties.

Mitochondrial neurogastrointestinal encephalomyopathy: an autosomal recessive disorder due to thymidine phosphorylase mutations

Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is an autosomal recessive disorder defined clinically by severe gastrointestinal dysmotility; cachexia; ptosis, ophthalmoparesis, or both; peripheral neuropathy; leukoencephalopathy; and mitochondrial abnormalities. The disease is caused by mutations in the thymidine phosphorylase (TP) gene. TP protein catalyzes phosphorolysis of thymidine to thymine and deoxyribose 1-phosphate. We identified 21 probands (35 patients) who fulfilled our clinical criteria for MNGIE. MNGIE has clinically homogeneous features but varies in age at onset and rate of progression. Gastrointestinal dysmotility is the most prominent manifestation, with recurrent diarrhea, borborygmi, and intestinal pseudo-obstruction. Patients usually die in early adulthood (mean, 37.6 years; range, 26-58 years). Cerebral leukodystrophy is characteristic. Mitochondrial DNA (mtDNA) has depletion, multiple deletions, or both. We have identified 16 TP mutations. Homozygous or compound heterozygous mutations were present in all patients tested. Leukocyte TP activity was reduced drastically in all patients tested, 0.009 +/- 0.021 micromol/hr/mg (mean +/- SD; n = 16), compared with controls, 0.67 +/- 0.21 micromol/hr/mg (n = 19). MNGIE is a recognizable clinical syndrome caused by mutations in thymidine phosphorylase. Severe reduction of TP activity in leukocytes is diagnostic. Altered mitochondrial nucleoside and nucleotide pools may impair mtDNA replication, repair, or both.

Differential features of patients with mutations in two COX assembly genes, SURF-1 and SCO2

We screened 41 patients with undiagnosed encephalomyopathies and cytochrome c oxidase (COX) deficiency for mutations in two COX assembly genes, SURF-1 and SCO2; 6 patients had mutations in SURF-1 and 3 had mutations in SCO2. All of the mutations in SURF-1 were small-scale rearrangements (deletions/insertions); 3 patients were homozygotes and the other 3 were compound heterozygotes. All patients with SCO2 mutations were compound heterozygotes for nonsense or missense mutations. All of the patients with mutations in SURF-1 had Leigh syndrome, whereas the 3 patients with SCO2 mutations had a combination of encephalopathy and hypertrophic cardiomyopathy, and the neuropathology did not show the typical features of Leigh syndrome. In patients with SCO2 mutations, onset was earlier and the clinical course and progression to death more rapid than in patients with SURF-1 mutations. In addition, biochemical and morphological studies showed that the COX deficiency was more severe in patients with SCO2 mutations. Immunohistochemical studies suggested that SURF-1 mutations result in similarly reduced levels of mitochondrial-encoded and nuclear-encoded COX subunits, whereas SCO2 mutations affected mitochondrial-encoded subunits to a greater degree. We conclude that patients with mutations in SURF-1 and SCO2 genes have distinct phenotypes despite the common biochemical defect of COX activity.

Analysis of mtDNA deletions in muscle by in situ hybridization

We compared the distribution of deleted mitochondrial DNA (Delta-mtDNA) in skeletal muscle of a patient with autosomal recessive (AR) and another with autosomal dominant (AD) progressive external ophthalmoplegia (PEO) by in situ hybridization (ISH). The patients studied had similar numbers of fibers deficient in cytochrome c oxidase (COX) activity (13.6% and 12.8%) and fibers with mitochondrial proliferation (5.5% and 5.3%). ISH suggested that each COX-deficient fiber contained a single species of Delta-mtDNA. Most deletions ablated the region between the genes encoding adenosine triphosphate (ATP) synthase subunit 8 and cytochrome b. Fibers that appeared to be depleted of mtDNA were also present. We conclude that muscle from patients with autosomally inherited PEO contains not only Delta-mtDNA but also focal depletion of mtDNA and that the distribution of these mtDNA defects appears to be similar. These changes most likely represent the common consequence of whatever genetic factors are responsible for the generation of Delta-mtDNA.

Melatonin acts on the nucleus accumbens to increase acetylcholine release and modify the motor activity pattern of rats

Brain microdialysis coupled to high performance liquid chromatography with electrochemical detection (HPLC-ED) was used to evaluate the influence of melatonin on extracellular concentration of acetylcholine (ACh) in the nucleus accumbens (NAc) of rats. Motor activity was simultaneously monitored during the dialysis sessions with an activity meter. Melatonin and prazosin were administered locally through the dialysis probe. It was found that melatonin dose-dependently increased accumbens ACh. Melatonin (3 microM) decreased horizontal activity and increased vertical activity, while another dose (100 microM) enhanced both horizontal and vertical activity. Prazosin, a putative melatonin antagonist, blocked the effects of melatonin on both motor activity and ACh release when given 20 min before melatonin. Overall, these results suggest that melatonin modulates the release of ACh in the NAc and the pattern of motor activity in the rat.

Reduced tolerance and cardiovascular response to ischemic pain in minor depression

BACKGROUND

A paradoxical association between a higher prevalence of clinical pain and a reduced sensitivity to brief experimental pain seems to exist during depression.

METHODS

We assessed the responses to sustained ischemic pain produced by a maximal effort tourniquet procedure in 32 controls and 11 individuals with minor depression (Zung autoscale > or =50). Stethoscopic blood pressures and heart rates were monitored throughout the procedure.

RESULTS

Measures of pain threshold, and measures of pain intensity and pain unpleasantness during the ischemic procedure were similar in depressed and control subjects. Yet, the overall numerical ratings of ischemic pain during the procedure was 28% higher and pain tolerance was 44% lower in depressed compared to control subjects. Clinical pain complaints were reported by 91% of depressed but only by 41% of control subjects (P = 0.01). Sustained ischemic pain induced significant elevations of systolic and mean arterial blood pressures in controls but not in depressed subjects.

LIMITATIONS

The main limitation of the present study was the preponderance of females in the depressed group. Yet, we did not find significant gender differences in the sensory-affective and autonomic responses to ischemic pain in our sample.

CONCLUSIONS

These findings suggest alterations in the sensory and autonomic nervous systems during minor depression.

Does the patient have a mitochondrial encephalomyopathy?

The ubiquitous nature of mitochondria, the dual genetic control of the respiratory chain, and the peculiar rules of mitochondrial genetics contribute to explain the extraordinary clinical heterogeneity of disorders associated with defects of oxidative phosphorylation (mitochondrial encephalomyopathies). To provide a practical approach to the diagnostic challenge posed by these conditions, we critically review the following criteria: (1) clinical presentation; (2) family history; (3) laboratory data; (4) neuroradiologic patterns; (5) standardized exercise testing; (6) muscle morphology; (7) muscle biochemistry; and (8) molecular genetic screening. Judicious sequential application of these tools should provide help in recognizing patients with mitochondrial disease and define the biochemical and molecular basis of the disorder for each patient. This knowledge is indispensable for accurate genetic counseling and prenatal diagnosis and is a prerequisite for the development of rational therapies, which are still woefully inadequate.

Fatal infantile cardioencephalomyopathy with COX deficiency and mutations in SCO2, a COX assembly gene

Mammalian cytochrome c oxidase (COX) catalyses the transfer of reducing equivalents from cytochrome c to molecular oxygen and pumps protons across the inner mitochondrial membrane. Mitochondrial DNA (mtDNA) encodes three COX subunits (I-III) and nuclear DNA (nDNA) encodes ten. In addition, ancillary proteins are required for the correct assembly and function of COX (refs 2, 3, 4, 5, 6). Although pathogenic mutations in mtDNA-encoded COX subunits have been described, no mutations in the nDNA-encoded subunits have been uncovered in any mendelian-inherited COX deficiency disorder. In yeast, two related COX assembly genes, SCO1 and SCO2 (for synthesis of cytochrome c oxidase), enable subunits I and II to be incorporated into the holoprotein. Here we have identified mutations in the human homologue, SCO2, in three unrelated infants with a newly recognized fatal cardioencephalomyopathy and COX deficiency. Immunohistochemical studies implied that the enzymatic deficiency, which was most severe in cardiac and skeletal muscle, was due to the loss of mtDNA-encoded COX subunits. The clinical phenotype caused by mutations in human SCO2 differs from that caused by mutations in SURF1, the only other known COX assembly gene associated with a human disease, Leigh syndrome.

Exercise intolerance due to mutations in the cytochrome b gene of mitochondrial DNA

BACKGROUND

The mitochondrial myopathies typically affect many organ systems and are associated with mutations in mitochondrial DNA (mtDNA) that are maternally inherited. However, there is also a sporadic form of mitochondrial myopathy in which exercise intolerance is the predominant symptom. We studied the biochemical and molecular characteristics of this sporadic myopathy.

METHODS

We sequenced the mtDNA cytochrome b gene in blood and muscle specimens from five patients with severe exercise intolerance, lactic acidosis in the resting state (in four patients), and biochemical evidence of complex III deficiency. We compared the clinical and molecular features of these patients with those previously described in four other patients with mutations in the cytochrome b gene.

RESULTS

We found a total of three different nonsense mutations (G15084A, G15168A, and G15723A), one missense mutation (G14846A), and a 24-bp deletion (from nucleotide 15498 to 15521) in the cytochrome b gene in the five patients. Each of these mutations impairs the enzymatic function of the cytochrome b protein. In these patients and those previously described, the clinical manifestations included progressive exercise intolerance, proximal limb weakness, and in some cases, attacks of myoglobinuria. There was no maternal inheritance and there were no mutations in tissues other than muscle. The absence of these findings suggests that the disorder is due to somatic mutations in myogenic stem cells after germ-layer differentiation. All the point mutations involved the substitution of adenine for guanine, but all were in different locations.

CONCLUSIONS

The sporadic form of mitochondrial myopathy is associated with somatic mutations in the cytochrome b gene of mtDNA. This myopathy is one cause of the common and often elusive syndrome of exercise intolerance.

A stop-codon mutation in the human mtDNA cytochrome c oxidase I gene disrupts the functional structure of complex IV

We have identified a novel stop-codon mutation in the mtDNA of a young woman with a multisystem mitochondrial disorder. Histochemical analysis of a muscle-biopsy sample showed virtually absent cytochrome c oxidase (COX) stain, and biochemical studies confirmed an isolated reduction of COX activity. Sequence analysis of the mitochondrial-encoded COX-subunit genes identified a heteroplasmic G-->A transition at nucleotide position 6930 in the gene for subunit I (COX I). The mutation changes a glycine codon to a stop codon, resulting in a predicted loss of the last 170 amino acids (33%) of the polypeptide. The mutation was present in the patient's muscle, myoblasts, and blood and was not detected in normal or disease controls. It was not detected in mtDNA from leukocytes of the patient's mother, sister, and four maternal aunts. We studied the genetic, biochemical, and morphological characteristics of transmitochondrial cybrid cell lines, obtained by fusing of platelets from the patient with human cells lacking endogenous mtDNA (rho0 cells). There was a direct relationship between the proportion of mutant mtDNA and the biochemical defect. We also observed that the threshold for the phenotypic expression of this mutation was lower than that reported in mutations involving tRNA genes. We suggest that the G6930A mutation causes a disruption in the assembly of the respiratory-chain complex IV.

Increased number of caveolae and caveolin-3 overexpression in Duchenne muscular dystrophy

Caveolae are small pockets or invaginations localized at the plasma membrane. Caveolins are the principal protein components of caveolae and play an important structural role in the formation of caveolae membranes. Here, we studied by freeze fracture and immunological techniques the spatial organization of caveolae at the muscle cell plasma membrane and the expression of caveolin-3 in Duchenne muscular dystrophy (DMD) muscle fibers. In DMD muscle, we found an increased number of caveolae at the sarcolemma that corresponds to an overexpression of caveolin-3 by immunohistochemistry and by Western blot analysis. These findings suggest a possible role for caveolae and caveolin-3 in the pathogenesis of DMD.

Phenotypic analysis of autosomal dominant hereditary spastic paraplegia linked to chromosome 8q

OBJECTIVE

To describe clinical, electrophysiologic, neuroimaging, and muscle biopsy features in a hereditary spastic paraplegia (HSP) kindred linked to a new HSP locus on chromosome 8q.

BACKGROUND

HSP is a genetically diverse group of disorders characterized by insidiously progressive spastic weakness in the legs. We recently analyzed a Caucasian kindred with autosomal dominant HSP and identified tight linkage to a novel HSP locus on chromosome 8q23-24.

METHODS

Clinical analysis, nerve conduction studies, electromyography, somatosensory evoked potentials, MRI of brain and spinal cord, and muscle biopsy for mitochondrial analysis were performed in members of the first HSP kindred linked to chromosome 8q.

RESULTS

Fifteen individuals showed insidiously progressive spastic paraparesis beginning between ages 22 and 60 years (average, 37.2 years). Spinal cord MRI in 1 moderately affected subject showed significant atrophy of the thoracic spinal cord as determined by cross-sectional area measurements. Somatosensory evoked potential recording, electromyography, nerve conduction studies, and muscle biopsy, including histochemical and biochemical analysis of mitochondrial function, were normal.

CONCLUSIONS

The phenotype in this family is that of typical, but severe, uncomplicated HSP. Other than apparently increased severity, there were no clinical features that distinguished this family from autosomal dominant HSP linked to loci on chromosomes 2p, 14q, and 15q. This clinical similarity between different genetic types of autosomal dominant HSP raises the possibility that genes responsible for these clinically indistinguishable disorders may participate in a common biochemical cascade. Normal results of muscle histochemical and biochemical analysis suggest that mitochondrial disturbance, a feature of chromosome 16-linked autosomal recessive HSP due to paraplegin gene mutations, is not a feature of chromosome 8q-linked autosomal dominant HSP and may not be a common factor of HSP in general.

Disconnection of cerebellar Purkinje cells in Kearns-Sayre syndrome

Kearns-Sayre syndrome (KSS) is a sporadic multisystem disorder due to rearrangements in mitochondrial DNA (mtDNA). To gain further insight into the pathogenesis of cerebellar dysfunction in KSS, antibodies against synaptophysin (SY) were used to identify presynaptic terminals and antibodies to calbindin D (CB) to identify Purkinje cells in the cerebellar cortex and in the dentate nucleus from two autopsied cases of KSS. By conventional neuropathology we found marked spongiform degeneration and by immunohistochemistry a disruption of presynaptic terminals and of the terminal arborizations of Purkinje cell axons on multipolar neurons of the dentate nucleus in the KSS patients. We suggest that a disconnection of Purkinje cells at the dentate nucleus may play a role in the pathogenesis of cerebellar ataxia in KSS.

Maternally inherited hearing loss in a large kindred with a novel T7511C mutation in the mitochondrial DNA tRNA(Ser(UCN)) gene

Thirty-six of 43 maternally related members of a large African American family experienced hearing loss. A muscle biopsy specimen from the proband showed cytochrome c oxidase (COX)-deficient fibers but no ragged-red fibers; biochemical analysis showed marked reduction of COX activity. A novel T7511C point mutation in the tRNA(Ser(UCN)) gene was present in almost homoplasmic levels (>95%) in the blood of 18 of 20 family members, and was also found in lower abundance in the other two. Single-fiber PCR showed that the mutational load was greater in COX-deficient muscle fibers. The tRNA(ser(UCN)) gene may be a "hot spot" for mutations associated with maternally transmitted hearing loss.

Exposure to 2500 lux increases serum melatonin in Venezuelan equine encephalomyelitis

When mice infected with the Venezuelan equine encephalomyelitis (VEE) virus were exposed to 2500 lux with a 12 h light: 12 h dark photoperiod, the serum levels of melatonin (MLT) remained constantly elevated. In mice exposed to 400 lux low levels of serum MLT were detected during the day and high levels during the night. An increase in the survival rate of the infected mice from 6 to 13 days after virus inoculation was also observed. The significant increment in the concentration of serum MLT produced by the high intensity light could be responsible for the longer survival rate of mice infected with the VEE virus.