Biomedical subjects

M Zeviani

Publications and source records attributed to M Zeviani.

At least 109 records · Page 6Linked to original sources

PubMed1995

Evidence of linkage between susceptibility to multiple sclerosis and HLA-class II loci in Italian multiplex families.

To verify whether multiallelic polymorphisms belonging to HLA class II genes are linked to multiple sclerosis (MS) in the Italian population, we studied 28 multiplex MS families originating from different areas of Italy. Allelic characterization was carried out by analysis of RFLPs and oligonucleotide typing. Evidence supporting the existence of linkage between MS susceptibility and the HLA class II loci DRB1, DQA1 and DQB1 was provided using two non-parametric tests, affected sib-pair analysis, and affected-pedigree-member (APM) analysis. The APM analysis also suggested the existence of genetic heterogeneity for the HLA class II loci and MS susceptibility in our series. Linkage disequilibrium between MS susceptibility and the haplotype DRB1*1501,DQA1*0102,DQB1*0602 was demonstrated by applying the transmission linkage disequilibrium test to our families. Finally, lod score analysis suggests that in our Italian families, MS susceptibility is conferred by HLA class II alleles according to a low-penetrance autosomal recessive mode of inheritance.

Alleles↗

PubMed1994

Order of six loci at 2q24-q31 and orientation of the HOXD locus.

HOXD, a gene cluster of 9 homeobox genes of the Antennapedia class; EVX2, a homeobox gene related to Drosophila-even-skipped gene; DLX1 and DLX2, two homeobox genes related to the Drosophila distal-less gene; and TTN and NEB, the genes for the two giant molecules titin and nebulin, both involved in the sarcomere structure, have been previously mapped to human 2q31-q32 and to mouse chromosome 2. We studied their relative order in human by applying FISH to three balanced chromosome rearrangements each with a breakpoint at 2q31. Unambiguous results led us to map these genes and to orient the HOXD locus along chromosome 2 according to the following order: cen, NEB, DLX1-DLX2, EVX2, HOXD (5'-3'), TTN, tel. All of these genes are part of a syntenic region covering 5-10 cM and conserved since the divergence of humans and rodents, and thus the same loci order should be present in mouse. FISH in metaphases of approximately 500 bands localized NEB to 2q24.1-q24.2, while HOXD and TTN were localized to 2q31.

Animals↗

PubMed1994

De novo and inherited deletions of the 5q13 region in spinal muscular atrophies.

Spinal muscular atrophies (SMAs) represent the second most common fatal autosomal recessive disorder after cystic fibrosis. Childhood spinal muscular atrophies are divided into severe (type I) and mild forms (types II and III). By a combination of genetic and physical mapping, a yeast artificial chromosome contig of the 5q13 region spanning the disease locus was constructed that showed the presence of low copy repeats in this region. Allele segregation was analyzed at the closest genetic loci detected by markers C212 and C272 in 201 SMA families. Inherited and de novo deletions were observed in nine unrelated SMA patients. Moreover, deletions were strongly suggested in at least 18 percent of SMA type I patients by the observation of marked heterozygosity deficiency for the loci studied. These results indicate that deletion events are statistically associated with the severe form of spinal muscular atrophy.

Alleles↗

PubMed1994

Single-stranded-DNA-binding proteins from human mitochondria and Escherichia coli have analogous physicochemical properties.

The gene for the mature human mitochondrial single-stranded-DNA binding protein (HsmtSSB) has been transferred into a protein-overproducing vector and expressed in Escherichia coli. The protein was purified to homogeneity and its physicochemical properties were investigated. From sequence comparison, HsmtSSB shows some similarities to the N-terminal part of the single-stranded DNA-binding protein (SSB) from E. coli (EcoSSB). Hydrodynamic measurements show the protein to be tetrameric and give a sedimentation coefficient of 4.1 S corresponding to a C-terminally shortened EcoSSB. Electron-microscopic images of the free protein show a globular tetrahedral structure. Binding of poly(desoxythymidylic acid) [poly(dT)] leads to a reduction of the tryptophan fluorescence of the protein up to 96%. Fluorescence titrations with poly(dT) show apparent binding-site sizes of 50-70 nucleotides/tetramer between 0.05 M and 2 M NaCl. Binding to poly(dT) proceeds in a nearly diffusion-controlled reaction with an association-rate constant kass of 4 x 10(8) M-1s-1. The rate-limiting step is the formation of a transient complex where less than four binding sites on the protein are involved and the reshuffling of the protein on the linear matrix is fast. Electron microscopy of the complex with poly(dT) using negative staining shows a nearly random distribution of the protein between the individual poly(dT) strands. This leads to the conclusion that the binding cooperativity is low (omega < 150). The two tryptophans of HsmtSSB were replaced by threonine and tyrosine. The environment of both residues is influenced by nucleic acid binding with mutations of Trp68 strongly reducing the DNA-binding affinity of the protein.

Binding Sites↗

PubMed1994

Mitochondrial myopathy: correlation between oxidative defect and mitochondrial DNA deletions at single fiber level.

In situ hybridization combined with immunohistochemical techniques has been applied to study patients affected by mitochondrial myopathies with large mitochondrial (mt)DNA deletions. All patients' muscle biopsies showed ragged red fibers (RRFs) and cytochrome oxidase (COX) deficiency. Two digoxigenin-labeled, polymerase chain reaction (PCR)-amplified DNAs were used as probes. One probe was designed to hybridize only with wild-type mtDNAs, while the other recognized both wild-type and deleted mtDNAs. Concomitant immunocytochemical analysis using antibodies against subunits II, III, (encoded by mtDNA) and IV (encoded by nuclear DNA) of COX was carried out. In our patients deleted mtDNAs are overexpressed in COX-negative RRFs, while wild-type mtDNAs are decreased in the same fibers. Immunohistochemistry studies show that COX IV is overexpressed in RRFs and that COX II and COX III subunits are still present. Deleted mtDNAs are spatially segregated in muscle fibers, where they interfere with the local population of normal mitochondrial genomes, causing a regional deficiency of the mitochondrial respiratory activity.

Adolescent↗

PubMed1994

The myelin basic protein gene is not a major susceptibility locus for multiple sclerosis in Italian patients.

To verify whether multiallelic polymorphism adjacent to the gene encoding for myelin basic protein is associated with or linked to multiple sclerosis in Italians, we studied 54 sporadic patients, 55 control subjects and 18 families with two or more affected individuals. Allelic typing was carried out by analysis of fragment length polymorphisms after DNA amplification by the polymerase chain reaction. The presence of linkage with the disease was tested according to either autosomal dominant or autosomal recessive modes of inheritance, and with or without the introduction of liability classes accounting for the age of the individuals. Furthermore sib-pair analysis was performed in 11 siblings. No evidence for association or linkage between the myelin basic protein gene polymorphism and multiple sclerosis was found. Our data indicate that in the Italian population the myelin basic protein gene does not play a major role in conferring genetic susceptibility to multiple sclerosis, and suggest that the latter is a heterogeneous phenomenon, possibly influenced by the different ethnic origin of the populations which have been investigated.

Adult↗

PubMed1994

Mitochondrial myopathies.

Major new advances in the genetic and biochemical characterization of mitochondrial myopathies are discussed, within a general presentation of this important new area of human pathology. Mitochondrial disorders can be due to mutations in either nuclear or mitochondrial genes involved in the synthesis of individual respiratory chain subunits or in their posttranslational control. Although no mutations of nuclear-encoded oxidative phosphorylation subunits have been reported so far in humans, numerous biochemically defined disorders are attributed to nuclear gene defects. In contrast, molecular lesions of mitochondrial DNA are recognized as an increasingly frequent cause of defective oxidative phosphorylation. Numerous new mutations recently have been identified, including both maternally inherited point mutations and sporadic large-scale rearrangements. In addition, the identification of new or overlap syndromes has substantially broadened the clinical spectrum of mitochondrial disorders. To gain insight into the pathogenesis of these disorders, the relationship between specific clinical presentations and the mitochondrial genotype has been intensively investigated. In most cases, the phenotypic expression of the mitochondrial DNA mutations depends on the interplay among the relative amount of mutated vs wild-type genomes, ie, the degree of mitochondrial heteroplasmy and its tissue and cell distribution, the reliance of the affected tissues on aerobic energy supply, the age and gender of the individual, and other still poorly understood factors including individual "nuclear genetic background" and environmental factors.

Cell Nucleus↗

PubMed1994

Defective respiratory capacity and mitochondrial protein synthesis in transformant cybrids harboring the tRNA(Leu(UUR)) mutation associated with maternally inherited myopathy and cardiomyopathy.

We studied the physiometabolic effects of a mitochondrial DNA (mtDNA) heteroplasmic point mutation, the A-->G3260 transition associated with maternally inherited myopathy and cardiomyopathy. To eliminate the possible influence of the autochthonous nuclear gene set, we fused myoblast-derived cytoplasts of a patient with a human tumoral cell line deprived of mtDNA (Rho degrees). The presence and amount of the mutant G3260 vs the wild-type A3260 were measured by solid phase minisequencing. We observed a marked reduction of the percentage of mutant mtDNA in the culture system compared with that measured in the donor's muscle biopsy, suggesting the presence of negative selection against the mutation. Furthermore, stable mitotic segregation of the two mtDNA populations was observed in 18 of 19 transformant clones, suggesting the presence of intraorganelle and possibly intracellular homoplasmy in the precursor cells of the donor. Several indexes of mtDNA-related respiratory capacity, including oxygen consumption, complex I- and complex IV-specific activities, and lactate production, were markedly abnormal in the clones containing a high proportion of mutant mtDNA, as compared with those containing homoplasmic wild-type mtDNA, possibly because of impaired mitochondrial protein synthesis. We conclude that (a) the A-->G3260 transition is indeed responsible for the mitochondrial disorder identified in the donor patient, and (b) transformant cybrid system gives direct evidence of the mitochondrial origin of a genetic disorder and should be adopted for the evaluation of the pathogenic potential of the mtDNA mutations.

Adult↗

PubMed1994

Remarkable recovery of visual function in a patient with Leber's optic neuropathy and multiple mutations of mitochondrial DNA.

Almost complete spontaneous recovery in visual function was observed in a male patient with Leber's hereditary optic neuropathy (LHON), in spite of the presence of several LHON-associated "major" and "minor" mutations of mitochondrial DNA. Our findings confirm that visual loss in LHON may be reversible, and challenge the hypothesis of a "synergistic" effect of multiple mtDNA mutations in the phenotypic expression of the disease.

Adolescent↗

PubMed1994

[Physical study of big fragments and search strategy of genes. Application to locus of infant spinal muscular atrophies].

Spinal muscular atrophies (SMA) represent the second most common fatal autosomal recessive disorder after cystic fibrosis. Childhood SMAs are divided into severe (type I) and mild forms (types II and III). By a combination of genetic and physical mapping, a YAC contig of the 5q13 region spanning the disease locus was constructed that showed the presence of low copy-repeats in this region. Allele segregation was analyzed at the closest genetic loci detected by markers C212 and C272 in 201 SMA families. Inherited and de novo deletions were observed in 10 SMA patients. Moreover, deletions were strongly suggested in at least 18% of SMA type I patients by the observation of marked heterozygosity deficiency for the loci studied. These results indicate that deletion events are statistically associated with the severe form of SMA.

Chromosome Mapping↗

PubMed1994

Mitochondrial diseases.

Mitochondrial diseases are heterogeneous and characterized by a primary defect of the mitochondrial energy output. Genetic defects of mitochondrial energy enzymes may be due to either nuclear DNA gene mutations or mitochondrial DNA (mtDNA) mutations. Among hereditary defects of nuclear-encoded mitochondrial enzymes, carnitine palmitoyltransferase II (CPT-II) deficiency and pyruvate dehydrogenase complex (PDHC) deficiency are of major interest to the neurologist. Several mutations in the CPT-II gene as well as in the X-linked E1 alpha subunit gene of PDHC have been reported and associated with different clinical phenotypes. mtDNA-related syndromes include mitochondrial encephalomyopathies (e.g. MELAS, MERRF, NARP, MIMyCa, etc.), 'pure' encephalopathies (e.g. LHON) and a few syndromes involving only non-neurological systems (e.g. Pearson's pancreas-bone marrow syndrome or diabetes mellitus). Three kinds of molecular lesions have been identified in mtDNA-related disorders: point mutations of protein-encoding mtDNA genes (mit- mutations), point mutations of mtDNA-tRNA genes (syn- mutations) and large-scale rearrangements of mtDNA (rho- mutations). Point mutations (mit- and syn+) are usually maternally inherited, while single large-scale mtDNA rearrangements are usually sporadic. Furthermore, mendelian traits leading to either qualitative or quantitative abnormalities of mtDNA (i.e. multiple mtDNA deletions and tissue-specific mtDNA depletion, respectively) are the first examples of genetic dysfunction of nuclear-mitochondrial communication. In most cases, the molecular detection of the known defects of mtDNA can be carried out by non-invasive techniques, thus making it an easy and relatively inexpensive procedure in the differential diagnosis of the mitochondrial disorders, a rapidly expanding area of clinical neurology.

DNA, Mitochondrial↗

PubMed1993

Cloning of human and rat cDNAs encoding the mitochondrial single-stranded DNA-binding protein (SSB).

We have retro-transcribed and amplified by PCR the full-length cDNAs specifying the rat and human precursors of the single-stranded mitochondrial DNA (mtDNA)-binding protein (mtSSB). Each deduced sequence is composed of a 16-amino-acid (aa) N-terminal basic pre-sequence and a mature protein (132 aa in humans and 135 aa in the rat). The mature proteins are highly conserved among themselves and with the mtSSB from Xenopus laevis (Xl). Moreover, three regions of the protein are similar to corresponding domains of the SSB of Escherichia coli and to the E. coli F-sex factor SSB, indicating the existence of a broad class of DNA-binding proteins with structural and functional similarities both in prokaryotes and in prokaryote-derived organelles of higher organisms.

Amino Acid Sequence↗

PubMed1993

Progressive myoclonus epilepsies: an electroclinical, biochemical, morphological and molecular genetic study of 17 cases.

Electroclinical, morphological, biochemical and molecular genetic data from 17 patients affected by progressive myoclonus epilepsies (PME) are reported. Twelve patients were characterized by prominent action myoclonus, sporadic seizures, mild ataxia, lack of dementia and persistence of normal EEG background activity; three patients showed a more rapid worsening of symptomatology, characterized by early mental impairment, massive and action myoclonus, cerebellar signs and tonic clonic seizures; in these patients EEG background activity was slow, even in early stages of the disease. In two patients, previously classified as cryptogenetic PME, a mitochondrial aetiology was recognized by the presence of ragged red fibers in muscle biopsy and by a reduction of the respiratory chains enzymes. Molecular genetical investigation of mtDNA demonstrated the reported heteroplasmic point mutation at nt 8344 of mtDNA in the two MERRF patients, while it was negative in all of the others.

Adolescent↗

PubMed1993

A MERRF/MELAS overlap syndrome associated with a new point mutation in the mitochondrial DNA tRNA(Lys) gene.

Several members of a three-generation kindred from Sardinia were affected by a maternally inherited syndrome characterized by features of both myoclonus epilepsy with ragged-red fibers (MERRF) and mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes (MELAS). Clinically, symptoms such as myoclonus epilepsy, neural deafness and ataxia were variably associated with stroke-like episodes and/or migrainous attacks. Morphologically, numerous MELAS-associated SDH-stained vessels were observed in muscle biopsies, either alone or in combination with ragged-red fibers, the morphological hallmark of MERRF. Sequence analysis of the mtDNA tRNA genes revealed the presence of a single, heteroplasmic T-->C transition at nt 8356, in the region of the tRNA(Lys) gene corresponding to the T-psi-C stem. The T-->C(8356) transition was exclusively found in the maternal lineage of our family, and the relative amount of the mutant mtDNA species in muscle was correlated with the severity of the clinical presentation. Therefore, we propose that the T-->C(8356) transition is responsible for the mitochondrial encephalomyopathy found in our family, and must be added to the expanding list of the pathogenetically relevant mutations of human mtDNA.

Acidosis, Lactic↗

PubMed1993

Respiratory chain and mitochondrial DNA in muscle and brain in Parkinson's disease patients.

There are several reports of a defect of complex I in the substantia nigra (SN) of Parkinson's disease (PD) patients. To evaluate whether this is specific to dopaminergic neurons or the phenotypically relevant consequence of a widespread failure of the mitochondrial oxidative phosphorylation (OXPHOS) system, we measured respiratory enzyme activities in muscle homogenates from 16 PD patients and eight age-matched controls, and in muscle isolated mitochondria of six PD patients and six age-matched controls. We found no difference between the PD and control groups. In addition, we detected, by polymerase chain reaction, the mitochondrial DNA (mtDNA) "common deletion" (CD) in muscle specimens of 14 of 17 PD patients, but we obtained similar results in age-matched controls. In both groups, the amount of CD-specific deleted (delta) mtDNA ranged from 0.0% to 0.1%. Our data suggest that PD cannot be attributed to a multisystem decline of mitochondrial OXPHOS, and that lesions of muscle mtDNA in PD are likely due to normal aging. However, there was a remarkable accumulation of delta mtDNA in the SN of a PD patient and an age-matched control, suggesting that the SN is exquisitely sensitive to age-dependent damage of the mitochondrial genome.

Adult↗

PubMed1992

Differential expression of genes specifying two isoforms of subunit VIa of human cytochrome c oxidase.

Subunit VIa of mammalian cytochrome c oxidase (COX; EC 1.9.3.1) exists in two isoforms, one present ubiquitously ('liver' isoform; COX VIa-L) and the other present only in cardiac and skeletal muscle (COX VIa-M). We have now isolated a full-length cDNA specifying human COX VIa-M. The deduced mature COX VIa-M polypeptide is 62% identical to the human COX VIa-L isoform, but is approximately 80% identical to the bovine and rat COX VIa-M isoforms, suggesting that the two COX VIa isoform-encoding genes arose prior to the mammalian radiation. Transcriptional analysis showed a tissue-specific pattern: whereas COXVIa-L is transcribed ubiquitously, COXVIa-M is transcribed only in heart and skeletal muscle. The cDNA specifying COX VIa-M is a prime candidate for use in investigations of Mendelian-inherited COX deficiencies with primary involvement of muscle.

Amino Acid Sequence↗

PubMed1992

Nucleus-driven mutations of human mitochondrial DNA.

Neuromuscular disorders due to abnormalities of mitochondrial energy supply have become an important area of human pathology. In particular, lesions of the mitochondrial genome (mtDNA), a small extra-nuclear chromosome which encodes 13 subunits of the respiratory chain complexes, are responsible for a steadily increasing number of neuromuscular syndromes. In addition to sporadic or maternally-inherited mutations, either qualitative or quantitative abnormalities of mtDNA can be transmitted as Mendelian traits, leading to well-defined mitochondrial encephalomyopathies. The latter are presumably caused by mutations in still unknown nucleus-encoded genes which deleteriously interact with the mitochondrial genome. These observations are of importance from both clinical and theoretical points of view, because they are the first examples of diseases produced by abnormalities of the nuclear control over mitochondrial biogenesis.

Base Sequence↗

PubMed1992

Defects of mitochondrial DNA.

In the past few years several syndromes have been associated with lesions of the human mitochondrial DNA. MtDNA is a small, circular extra-nuclear chromosome encoding essential components of the respiratory chain. MtDNA-related syndromes can be divided into two groups: mitochondrial encephalomyopathies, characterized by the presence of ragged-red fibres (RRF) as the morphological hallmark, or "pure" encephalopathies with no gross morphological abnormalities in muscle. The first group includes myoclonic epilepsy with ragged-red fibres (MERRF), mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes (MELAS), Kearns-Sayre syndrome (KSS), chronic progressive external ophthalmoplegia (CPEO) and a new entity, maternally inherited myopathy and cardiomyopathy. The second group includes Leber's Hereditary Optic Neuroretinopathy (LHON) and the newly described ataxia-retinitis pigmentosa-dementia complex. Three kinds of molecular lesions have been identified: point mutations of protein encoding mtDNA-genes (similar to yeast mit- mutations); point mutations of mtDNA-tRNA genes (similar to yeast syn- mutations); and large-scale rearrangements of mtDNA (similar to yeast rho- mutations). In general, "mit-" mutations are responsible for non-RRF encephalopathies, while "syn-" and "rho-" mutations are associated with mitochondrial encephalomyopathies with RRF. Furthermore, point mutations (mit- and syn-) are usually maternally- inherited, while large-scale mtDNA rearrangements are either sporadic or inherited as mendelian traits. In most cases, the molecular detection of the known defects of mtDNA can be carried out by non-invasive techniques, thus making it an easy and relatively inexpensive procedure in the differential diagnosis of the mitochondrial disorders, a rapidly expanding area of clinical neurology.

DNA, Mitochondrial↗