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Biomedical subjects

S Shanske

Publications and source records attributed to S Shanske.

At least 73 records · Page 4Linked to original sources
PubMed1997

Two large Spanish pedigrees with nonsyndromic sensorineural deafness and the mtDNA mutation at nt 1555 in the 12s rRNA gene: evidence of heteroplasmy.

We describe two unrelated Spanish families with isolated sensorineural hearing loss. In both pedigrees, the deafness was transmitted maternally, which suggested a mitochondrial, DNA (mtDNA) defect. Within the same pedigree, some relatives showed aminoglycoside-induced deafness, whereas others were not exposed to aminoglycosides before the onset of hearing loss. Molecular genetic analysis in both families showed the A-to-G transition at nt 1555 (A1555G) in the mitochondrial 12S rRNA gene. In one pedigree, the mutation was homoplasmic; in the other, it was heteroplasmic. To assess the frequency of this mutation, we screened 42 patients of various ethnic backgrounds with isolated sensorineural hearing loss; none harbored the A1555G mutation. This is the first report of heteroplasmy in a family with isolated sensorineural deafness associated with the A1555G mutation.

Amino Acid Sequence↗
PubMed1997

Mitochondrial encephalomyopathy with coenzyme Q10 deficiency.

Coenzyme Q10 (CoQ10) transfers electrons from complexes I and II of the mitochondrial respiratory chain to complex III. There is one published report of human CoQ10 deficiency describing two sisters with encephalopathy, proximal weakness, myoglobinuria, and lactic acidosis. We report a patient who had delayed motor milestones, proximal weakness, premature exertional fatigue, and episodes of exercise-induced pigmenturia. She also developed partial-complex seizures. Serum creatine kinase was approximately four times the upper limit of normal and venous lactate was mildly elevated. Skeletal muscle biopsy revealed many ragged-red fibers, cytochrome c oxidase-deficient fibers, and excess lipid. In isolated muscle mitochondria, impaired oxygen consumption was corrected by the addition of decylubiquinone. During standardized exercise, ventilatory and circulatory responses were compatible with a defect of oxidation-phosphorylation, which was confirmed by near-infrared spectroscopy analysis. Biochemical analysis of muscle extracts revealed decreased activities of complexes I+II and I+III, while CoQ10 concentration was less than 25% of normal. With a brief course of CoQ10 (150 mg daily), the patient reported subjective improvement. The triad of CNS involvement, recurrent myoglobinuria, and ragged-red fibers should alert clinicians to the possibility of CoQ10 deficiency.

Adult↗
PubMed1997

Heterogeneous clinical presentation of the mtDNA NARP/T8993G mutation.

To obtain a better molecular definition of patients with syndromic retinitis pigmentosa, we screened for mitochondrial DNA (mtDNA) alterations of the two ATPase genes and 22 tRNA-coding sequences in 10 patients whose features resembled NARP (neuropathy, ataxia, and retinitis pigmentosa) syndrome. In two patients, one of whom showed features mimicking Kearns-Sayre syndrome, we identified a heteroplasmic T8993G mutation (average 80%) in the mitochondrial ATPase 6 gene. There was no mutated mtDNA in muscle and leukocytes from the mother of one patient or in leukocytes from his brother, suggesting a rapid segregation of the mutated nucleotide. MtDNA analysis should be considered in the differential diagnosis of patients with syndromic retinitis pigmentosa.

Adult↗
PubMed1996

Molecular basis of muscle phosphoglycerate mutase (PGAM-M) deficiency in the Italian kindred.

Human muscle phosphoglycerate mutase (PGAM-M) deficiency is associated with exercise intolerance, muscle cramps, chronic serum CK elevation, and recurrent episodes of myoglobinuria. Ten patients have been described: 7 African Americans, 1 African, and 2 Caucasians from the Italian kindred described here. Molecular genetic analysis has revealed three different mutations in the PGAM-M gene. The propositus of the Italian family was homozygous for a unique point mutation at codon 90 in exon 1, a C-to-T transition converting an encoded arginine to tryptophan. His sister, who had similar complaints, was also homozygous for this mutation while the paternal grandfather, both parents, a brother and a nephew of the propositus were heterozygous for the mutation. Our studies exclude that PGAM-M deficiency is limited to African Americans, and suggest that the molecular heterogeneity of this rare disorder may be due to a "founder effect" in different ethnic groups.

Adult↗
PubMed1996

Multiple mitochondrial DNA deletions in sporadic inclusion body myositis: a study of 56 patients.

Inclusion body myositis, a chronic inflammatory disorder, is the most common cause of myopathy in adults over the age of 50. Diagnosis is based on clinical features and distinctive morphological findings by both light and electron microscopy. The causes of inclusion body myositis are still unknown. Ultrastructural mitochondrial changes and ragged-red fibers are common in patients with sporadic inclusion body myositis, and multiple [correction of mutiple] mitochondrial DNA (mtDNA) deletions have been reported in 3 such patients, suggesting that mtDNA mutations may have a pathogenetic role. We studied 56 patients with sporadic inclusion body myositis, using a combination of clinical, morphological, biochemical, and molecular genetic analyses to determine the frequency and the distribution of mtDNA deletions. Using the polymerase chain reaction, we found multiple mtDNA deletions in 73% of patients, compared to 40% of normal age-matched control subjects and 47% of disease control subjects. The presence of deletions correlated with morphological evidence of ragged-red, cytochrome c oxidase-negative fibers, and with defects of complexes I and IV of the electron transport chain. Although aging may account for a proportion of mtDNA deletions in patients with sporadic inclusion body myositis and control subjects, mtDNA alterations may be accelerated in sporadic inclusion body myositis.

Adult↗
PubMed1996

Mitochondrial DNA and RNA processing in MELAS.

Mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS), a maternally inherited disorder, is usually associated with a point mutation in mitochondrial DNA (mtDNA) at position 3,243 in the tRNA Leu(UUR) gene. To further study the pathogenesis of MELAS, we analyzed tissues from 8 MELAS-3,243 patients. Southern blot analysis showed an increase in the ratio of mtDNA to nuclear DNA in almost all tissues examined, implying that mitochondrial proliferation is ubiquitous and is not confined to ragged-red fibers in muscle. By northern blot analysis, we demonstrated increased steady-state levels of RNA 19, a polycistronic transcript corresponding to the 16S rRNA + tRNA Leu(UUR) + ND1 genes (which are contiguous in the mtDNA) in heart, kidney, and muscle. These results provide further evidence that altered mitochondrial nucleic acid metabolism may have pathogenic significance in MELAS.

Adult↗
PubMed1996

Comparative biochemical studies in fibroblasts from patients with different forms of Leigh syndrome.

We have compared respiratory chain enzyme activities, ATP synthesis, and ATP hydrolysis in cultured fibroblast mitochondria from patients with Leigh syndrome (LS) due to: (i) cytochrome oxidase (COX) deficiency (#6); (ii) pyruvate dehydrogenase complex (PDHC) deficiency (#4); and (iii) maternally inherited LS (MILS) with the T8993G mutation in the ATPase 6 gene of mtDNA (#5). Enzyme activities were normal in patients with MILS and variably decreased in those with COX and PDHC deficiency. ATP hydrolysis was normal or mildly decreased in all three groups. In contrast, ATP synthesis was decreased in all patients but more markedly in those with MILS, and especially with pyruvate/malate as substrate. These studies show that impaired ATP production is the common feature of all three forms of LS, but it is both more severe and more specific in MILS, consistent with the genetic defect.

Adenosine Triphosphatases↗
PubMed1996

Molecular characterization of myophosphorylase deficiency in a group of patients from northern Italy.

We studied a group of 14 patients from Northern Italy with myophosphorylase deficiency. The disease presented considerable clinical and biochemical heterogeneity, which was reflected at the molecular level. The clinical presentation was typical in 3 patients, mild in 7 (exercise intolerance), and severe in 4 (fixed weakness). Enzyme activity was undetectable in 10 patients, below 3% of control in 3, and 13% of control in one. Enzymatic protein was detectable immunologically only in 1 patient. Myophosphorylase mRNA was present in 8 patients, but in 7 of them it was reduced in amount. Two patients were homozygous for the common nonsense R49X mutation, 5 were heterozygous. Two missense mutations not previously observed were identified in this group of patients. The frequency of alleles with the R49X mutation was significantly lower in this group of patients than in previously reported series. Myophosphorylase deficiency is genetically heterogeneous even among patients living in a small region and with a common ethnic background.

Adolescent↗
PubMed1996

Cloning of bovine muscle glycogen phosphorylase cDNA and identification of a mutation in cattle with myophosphorylase deficiency, an animal model for McArdle's disease.

Genetic defects of myophosphorylase in humans cause a metabolic myopathy (McArdle's disease) characterized by exercise intolerance, cramps, and recurrent myoglobinuria. Recently, a breed of cattle with myophosphorylase deficiency has been identified: this is the first animal model of McArdle's disease. To define the molecular genetic error in the cattle, we cloned and sequenced the wild-type bovine myophosphorylase cDNA. Homology to human cDNA is 95.8% for the amino acid sequence, and 92.0% for the nucleotide sequence. Sequence homology to rabbit cDNA is 97.3% in amino acid, 90.8% in nucleotide. In the cDNA fragments amplified by RT-PCR from muscle RNA of the cattle with myophosphorylase deficiency, we identified a C-to-T substitution, changing an encoded arginine (CGG) to tryptophan (TGG) at codon 489. The mutant residue is adjacent to pyridoxal phosphate binding sites and to an active site residue, and the sequence around this mutation is highly conserved in different species.

Animals↗
PubMed1996

Adult-onset MELAS. Evidence for involvement of neurons as well as cerebral vasculature in strokelike episodes.

BACKGROUND: We report a 46-year-old woman with implications regarding pathogenesis of strokelike episodes in MELAS (mitochondrial encephalomyopathy, lactic acidosis, and strokelike episodes). She had a 10-month history of episodic seizures, strokes, cognitive decline, vomiting, and ileus. She also had sensorineural hearing loss, insulin-dependent diabetes mellitus of several years' duration, and persistent lactic acidosis. Family history was pertinent for a similar syndrome in her deceased mother (onset in her sixties), for hearing loss and diabetes mellitus in two brothers, and for hearing loss in her only child, a son. CASE DESCRIPTION: Serial MRIs of the brain revealed severe but evanescent cerebral cortical abnormalities. A left temporal brain biopsy was performed to exclude encephalitis. Light microscopy revealed a diffuse fibrillary gliosis with abundant reactive gemistocytes, focal evidence of ischemic neuronal injury, and edema. Electron microscopy revealed bizarre enlarged mitochondria and changes consistent with cellular edema. Succinate dehydrogenase staining was strongly reactive within cerebral blood vessels and within neurons. A point mutation was subsequently found at nt 3243 of the mitochondrial tRNA(Leu(UUR) gene in peripheral leukocytes and in brain, confirming the clinical diagnosis of MELAS. Quantitation revealed that 82% of brain mitochondria carried the disease mutation, indicating that most, if not all, tissues were affected. CONCLUSIONS: Our findings suggest that strokelike episodes in MELAS result from defects in neuronal metabolism, as well as in cerebral vasculature.

Age of Onset↗
PubMed1996

Clinical heterogeneity associated with the mitochondrial DNA T8993C point mutation.

The mitochondrial DNA (mtDNA) point mutation T8993G has been associated with maternally inherited Leigh syndrome (MILS) when very abundant (> 95%). MILS patients are usually severely affected and die in early infancy. In 1993, a novel T8993C point mutation was described in a juvenile form of Leigh syndrome (LS) characterized by a less aggressive clinical course. We describe four unrelated T8993C patients who had diverse, relatively mild, clinical manifestations. Polymerase chain reaction-restriction fragment length polymphorphism analysis showed that the heteroplasmic T8993C point mutation was very abundant in several tissues from all four patients (94.2 +/- 1.5%) but was less copious in blood from 20 maternal relatives. ATP production in mitochondria isolated from skin fibroblasts in three patients was normal, whereas in one patient it was decreased to 20-35% of controls. These findings suggest that the T8993C mutation is less severe than the more common T8993G mutation.

Adenosine Triphosphate↗
PubMed1996

Diagnosis of McArdle's disease by molecular genetic analysis of blood.

We analyzed leukocyte DNA from 32 patients with suspected McArdle's disease, 24 of whom had biochemically or histochemically proven myophosphorylase deficiency. We found that 19 were homozygous for the most common mutation at codon 49, 2 were compound heterozygotes, and 1 was a manifesting heterozygote. In six patients, we could find only one mutant allele, suggesting a still unidentified mutation on the second allele. We were unable to identify any of the known mutations in four patients. Our findings indicate that the diagnosis of McArdle's disease can be established in approximately 90% of patients using DNA isolated from leukocytes, thereby avoiding muscle biopsy.

Adult↗
PubMed1996

Maternally inherited cardiomyopathy and hearing loss associated with a novel mutation in the mitochondrial tRNA(Lys) gene (G8363A).

A novel G8363A mutation in the mtDNA tRNA(Lys) gene was associated, in two unrelated families, with a syndrome consisting of encephalomyopathy, sensorineural hearing loss, and hypertrophic cardiomyopathy. Muscle biopsies from the probands showed mitochondrial proliferation and partial defects of complexes I, III, and IV of the electron-transport chain. The G8363A mutation was very abundant (>95%) in muscle samples from the probands and was less copious in blood from 18 maternal relatives (mean 81.3% +/- 8.5%). Single-muscle-fiber analysis showed significantly higher levels of mutant genomes in cytochrome (c) oxidase-negative fibers than in cytochrome (c) oxidase-positive fibers. The mutation was not found in >200 individuals, including normal controls and patients with other mitochondrial encephalomyopathies, thus fulfilling accepted criteria for pathogenicity.

Adolescent↗
PubMed1995

Myopathy, lactic acidosis, and sideroblastic anemia: a new syndrome.

We describe 2 sibs (brother and sister) with myopathy, sideroblastic anemia, lactic acidosis, mental retardation, microcephaly, high palate, high philtrum, distichiasis, and micrognathia. Very low levels of cytochromes a, b, and c were detected in the patients' muscle mitochondria. Deposition of iron within the mitochondria of bone marrow erythroblasts was observed on electron microscopy. Irregular and enlarged mitochondria with paracrystalline inclusions were also seen on electron microscopy of the patients' muscle specimen. Examination of DNA from the affected sibs showed no deletions in the mitochondrial DNA nor the mutations identified in the syndromes of mitochondrial myopathy, encephalopathy, lactic acidosis, and strokelike episodes (MELAS) or myoclonus, and epilepsy associated with rugged-red fibers (MERRF). Since the parents were first cousins and 2 of 6 sibs (male and female) were affected, we suggest that the syndrome expressed by our patients represents a previously unknown autosomal recessive disorder that includes mitochondrial myopathy, lactic acidosis, and sideroblastic anemia.

5-Aminolevulinate Synthetase↗
PubMed1995

A novel mitochondrial ATPase 6 point mutation in familial bilateral striatal necrosis.

A T-to-C transition at nucleotide (nt) 9176 in the mitochondrial adenosine triphosphatase 6 (ATPase 6) gene was detected in 2 brothers with a neurological disorder resembling Leigh syndrome. The mutation was also present in the 2 other siblings and in the mother, who were asymptomatic. In the more severely affected boy (the proband), the mutation was homoplasmic in muscle, leucocytes, and fibroblasts. In leucocytes from his affected brother, 98% of mtDNA was mutant. Heteroplasmy of varying degrees was seen in leucocytes from the mother and the 2 unaffected siblings. The mutation changes a highly conserved leucine residue near the carboxyl terminus of the mitochondrial ATPase 6 subunit to proline. It could not be detected in 168 control subjects. Studies of ATP synthesis and hydrolysis in fibroblasts from the proband were normal.

Base Sequence↗
PubMed1995

Myophosphorylase deficiency associated with rhabdomyolysis and exercise intolerance in 6 related Charolais cattle.

A Charolais calf presented to the Veterinary Medical Teaching Hospital with a history of recumbency following forced exercise. The calf was unable to stand, and had severe rhabdomyolysis, dehydration, and electrolyte imbalance. Blood selenium concentrations were within normal limits. A complete absence of histochemical staining for phosphorylase was apparent in muscle biopsies. Five other animals in the herd also had exercise intolerance and had a complete absence of phosphorylase staining in muscle biopsies. Biochemical analyses confirmed a deficiency of myophosphorylase (range 0-0.3 mumol/g per minute: normals 15-27) with normal to slightly elevated muscle glycogen concentrations. Pedigrees from all affected animals showed a common ancestor on the sire's and dam's side of each phosphorylase-deficient animal, suggesting an autosomal recessive transmission. Although myophosphorylase deficiency was described in humans (McArdle's disease) over 40 years ago, these cattle represent the first animal model for this disease.

Animals↗