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S Shanske

Publications and source records attributed to S Shanske.

At least 55 records · Page 3Linked to original sources
PubMed1998

A splice junction mutation in the alpha(M) gene of phosphorylase kinase in a patient with myopathy.

In a 28-year-old man with myopathy and phosphorylase kinase (PhK) deficiency, we found a G-to-C substitution at the 5' end of an intron in the muscle-specific alpha-subunit gene. The mutation destroys the high-consensus GT sequences at the 5' splice junction of the intron, which causes skipping of the preceding exon. This is the second molecular genetic defect identified in the myopathic variant of PhK deficiency.

Adult↗
PubMed1998

Glycogen storage disease type II: identification of four novel missense mutations (D645N, G648S, R672W, R672Q) and two insertions/deletions in the acid alpha-glucosidase locus of patients of differing phenotype.

Glycogen storage disease type II (GSDII), an autosomal recessive myopathic disorder, results from deficiency of lysosomal acid alpha-glucosidase. We searched for mutations in an evolutionarily conserved region in 54 patients of differing phenotype. Four novel mutations (D645N, G448S, R672W, and R672Q) and a previously described mutation (C647W) were identified in five patients and their deleterious effect on enzyme expression demonstrated in vitro. Two novel frame-shifting insertions/deletions (delta nt766-785/insC and +insG@nt2243) were identified in two patients with exon 14 mutations. The remaining three patients were either homozygous for their mutations (D645N/D645 and C647W/C647W) or carried a previously described leaky splice site mutation (IVS1-13T-->G). For all patients "in vivo" enzyme activity was consistent with clinical phenotype. Agreement of genotype with phenotype and in vitro versus in vivo enzyme was seen in three patients (two infantile patients carrying C647W/C647W and D645N/+insG@nt2243 and an adult patient heteroallelic for G648S/IVS1-13T-->G). Relative discordance was found in a juvenile patient homozygous for the non-expressing R672Q and an adult patient heterozygous for the minimally expressing R672W and delta nt766-785/+insC. Possible explanations include differences in in vitro assays vs in vivo enzyme activity, tissue specific expression with diminished enzyme expression/stability in fibroblasts vs muscle, somatic mosaicism, and modifying genes.

Adult↗
PubMed1998

Study of mitochondrial DNA depletion in muscle by single-fiber polymerase chain reaction.

We studied muscle biopsies from 3 children with a mitochondrial myopathy characterized histochemically by the presence of ragged-red fibers (RRF) and various numbers of cytochrome c oxidase (COX)-negative fibers. We quantitated the absolute amounts of total mitochondrial DNA (mtDNA) in isolated normal COX-positive muscle fibers and in COX-negative RRF. There was severe mtDNA depletion in all fibers from the two most severe cases. In the third case mtDNA depletion could not be established with conventional diagnostic tools, but it was documented in single COX-negative fibers; COX-positive fibers showed the same amounts of mtDNA as fibers from aged-matched controls. Our observations indicate that mtDNA single-fiber PCR quantitation is a highly sensitive and specific method for diagnosing cases with focal mtDNA depletion. This method also allows one to correlate amounts of mtDNA with histochemical phenotypes in individual fibers from patients and age-matched controls, thereby providing important information about the functional role of residual mtDNA.

Biopsy↗
PubMed1998

The mitochondrial DNA A8344G mutation in Leigh syndrome revealed by analysis in paraffin-embedded sections: revisiting the past.

In 1975, we presented the results of a study on a family with a constellation of features that included a chronic spinocerebellar syndrome, neuropathologically proven Leigh syndrome, and sudden death in infancy or childhood affecting several members over three generations. Inheritance was thought to be autosomal dominant. Twenty years later, we reinterpreted the inheritance pattern as maternal. Mitochondrial DNA (mtDNA) extracted from paraffin-embedded brain samples from the proband revealed the A8344G myoclonic epilepsy and ragged-red fiber (MERRF) mutation as the molecular basis for this multifaceted neurological syndrome. This re-evaluation of archival material is an instructive example of "medical archeopathology."

Adolescent↗
PubMed1998

Primary adrenal insufficiency in a child with a mitochondrial DNA deletion.

Mitochondrial disorders can affect any organ system, but certain tissues, such as skeletal muscle, heart, and brain are more susceptible to oxidative phosphorylation defects because of their high energy requirements. Endocrinological manifestations, especially diabetes mellitus, are common but they rarely dominate the clinical picture. We describe a 5-year-old girl who died of primary adrenal insufficiency with a mitochondrial disease. Biochemical studies in muscle showed decreased respiratory chain enzyme activities. We detected a novel 7.0 kb mtDNA deletion in muscle form the proband, but not in her mother's white blood cells. Our findings further enlarge the spectrum of clinical presentation associated with mitochondrial DNA deletions.

Adrenal Insufficiency↗
PubMed1998

Comparative biochemical studies of ATPases in cells from patients with the T8993G or T8993C mitochondrial DNA mutations.

We performed comparative biochemical studies in cultured fibroblast mitochondria from patients with the T8993G or the T8993C point mutations in the ATPase 6 gene of mitochondrial DNA. We found that ATP production was much more severely decreased in cells from patients with the T8993G mutation than in those from patients with the T8993C mutation. Kinetic studies suggest that both mutations affect only the F0 sector of the mitochondrial ATPase complex. We conclude that these two mutations, which result in the substitution of different amino acids at the same site of the ATPase, result in an enzyme with different biochemical characteristics.

Adenosine Triphosphatases↗
PubMed1998

Combined defects of muscle phosphofructokinase and AMP deaminase in a child with myoglobinuria.

A 14-year-old boy with exercise-related myalgia and cramps had several episodes of myoglobinuria since early childhood. An episode at 2 years of age caused acute renal failure. Histochemical and biochemical analysis of muscle showed a combined defect of phosphofructokinase (PFK) and adenosine monophosphate (AMP) deaminase. DNA analysis showed that the patient was homozygous for a G-to-C substitution at codon 39 of the PFK gene (previously described in an Italian patient) and for the common mutation found in AMP deaminase deficiency.

AMP Deaminase↗
PubMed1998

Myoclonus epilepsy with ragged red fibers and multiple mtDNA deletions.

In a patient with clinical features of myoclonus epilepsy with ragged red fibers (MERRF), molecular genetic analysis of mitochondrial DNA did not show either of the two point mutations typically associated with MERRF but did show multiple deletions by Southern blot. This case further illustrates the heterogeneity observed with mtDNA mutations.

Adolescent↗
PubMed1998

Clinical manifestations of mitochondrial DNA depletion.

OBJECTIVE: We studied five new patients with mitochondrial DNA (mtDNA) depletion to better define the clinical spectrum of this disorder. BACKGROUND: mtDNA depletion has been associated with myopathy or hepatopathy, or both, in infants and young children. Involvement of the CNS and peripheral nervous system has not been clearly established. METHODS: We reviewed the clinical course and performed morphologic, biochemical, and genetic analyses of muscle samples from five patients. RESULTS: Age at onset ranged from 3 months to 5 years, and one patient survived until age 10 1/2 years. Two patients had laboratory and clinical features reminiscent of dystrophinopathy, two had evidence of brain involvement, and two had peripheral neuropathy. Muscle biopsy specimens in all patients showed abundant ragged-red fibers. Biochemistry showed cytochrome c oxidase deficiency in all patients tested and decreased activities of other respiratory chain complexes in some. CONCLUSIONS: Inheritance appeared to be autosomal recessive, suggesting that mutations in nuclear DNA are responsible for mtDNA depletion. mtDNA depletion should be considered in children with mitochondrial disorders of uncertain etiology, and criteria for diagnosis are proposed.

Blotting, Southern↗
PubMed1998

Molecular genetic analysis of McArdle's disease in Spanish patients.

We analyzed leukocyte DNA of 19 patients from 12 Spanish families with McArdle's disease (myophosphorylase deficiency). In 15 patients, the enzyme defect was documented histochemically in muscle, and in four the diagnosis was based on clinical and laboratory data. Three patients were homozygous and six were heterozygous for the nonsense mutation at codon 49 (R49X). Our findings indicate that the R49X mutation, which is common in English and American patients, is also present in Spanish patients with McArdle's disease, but at a lower frequency.

Adult↗
PubMed1998

Missense mutation in the mtDNA cytochrome b gene in a patient with myopathy.

A patient with progressive exercise intolerance, proximal weakness, and complex III deficiency in skeletal muscle had a missense mutation in the cytochrome b gene of mitochondrial DNA (G15762A). The mutation, which leads to the substitution of a highly conserved amino acid (G339E), was heteroplasmic (85%) in the patient's muscle and was not present in 100 individuals of different ethnic backgrounds. These data strongly suggest that this molecular defect is the primary cause of the myopathy.

Adult↗
PubMed1997

Identification of a novel mutation in the mtDNA ND5 gene associated with MELAS.

We report a novel G13513A mutation in the mitochondrial ND5 gene in a patient who had morphologically and biochemically abnormal muscle mitochondria and died at age 45 with a diagnosis of MELAS (mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes). The mutation affects an evolutionarily conserved nucleotide and was heteroplasmic in muscle, leukocytes, and several autopsy tissues, including brain. The mutation was less abundant (<5%) in leukocytes from an asymptomatic sister and was not found in over 100 controls, thus satisfying accepted criteria for pathogenicity. Our report reinforces the concept of genetic heterogeneity in MELAS and confirms that MELAS can be due to mutations in polypeptide-coding mtDNA genes.

Amino Acid Sequence↗
PubMed1997

High proportions of mtDNA duplications in patients with Kearns-Sayre syndrome occur in the heart.

Kearns-Sayre syndrome (KSS) is a sporadic multisystem mitochondrial disorder characterized by progressive external ophthalmoplegia, pigmentary retinopathy, onset before age 20, and severe cardiac conduction defects that can lead to death. KSS patients harbor partial deletions of mitochondrial DNA (delta-mtDNA), sometimes associated with the corresponding mtDNA duplication (dup-mtDNA). As reports on the distribution of dup-mtDNAs among KSS tissues are scarce, we searched for the presence of dup-mtDNAs in different autopsy tissues of two such patients, one of whom carried the so-called "common deletion." Using a newly developed long polymerase chain reaction (PCR) protocol in conjunction with Southern blot analyses, we found dup-mtDNAs in most of the examined tissues from both patients. The proportion of dup-mtDNA in these tissues was much lower than the proportion of delta-mtDNA, with one notable exception: in both patients, we found an unusually high level of dup-mtDNA in the heart. These data suggest that dup-mtDNAs may be more stable in heart tissue of KSS patients than in other long-lived postmitotic tissues.

Adolescent↗
PubMed1997

Oxidative phosphorylation dysfunction does not increase the rate of accumulation of age-related mtDNA deletions in skeletal muscle.

Several reports described an age-related accumulation of a particular mitochondrial DNA (mtDNA) deletion ('common deletion') in post-mitotic tissues. These findings led to the hypothesis that free radicals generated inside the mitochondria could damage mtDNA during a normal life span. The impaired electron transfer function resulting from mtDNA damage would increase the production of free radicals creating a vicious cycle. If this vicious cycle is an important player in the somatic accumulation of mtDNA deletions, patients with impaired oxidative phosphorylation (regardless of the primary defect) should have an accelerated accumulation of mtDNA deletions. We tested this hypothesis by performing three analyses: (a) comparing the amounts of the mtDNA 'common deletion' in normal controls and patients with genetically characterized mitochondrial disorders associated with pathogenic mtDNA point mutations or deletions other than the common deletion; (b) analyzing the co-segregation of the age-related mtDNA common deletion with a pathogenic mtDNA point mutation; and (c) by the detection of multiple mtDNA deletions by long PCR in controls and patients with mitochondrial disorders. We observed a positive correlation between age and common deletion levels in controls (r = 0.80) and patients (r = 0.69). The slopes of the curves were similar, suggesting that the rate of accumulation of the age-related common deletion was the same in both groups. We could not find a co-segregation of the pathogenic point mutated mtDNA molecules with the common deletion nor increased number of age-related deletions in patients. Our data do not support the hypothesis that a vicious cycle (damage to mtDNA would affect the respiratory function, leading to the generation of more free radicals, which in turn would provoke additional mtDNA damage) is an important factor in the accumulation of age-related mtDNA deletions.

Adolescent↗
PubMed1997

Maternally inherited encephalopathy associated with a single-base insertion in the mitochondrial tRNATrp gene.

We identified a single thymidine insertion at nucleotide position 5537 (T5537i) in the mitochondrial DNA transfer RNA gene for tryptophan in a family in which the proband had a progressive neurological disorder and his brother died in infancy of Leigh syndrome. Muscle biopsy from the proband showed subsarcolemmal proliferation of mitochondria and decreased activities of oxidative metabolism enzymes, in particular complex IV. Complex IV was also severely reduced in autopsy tissues, including heart and brain tissues, from the Leigh syndrome infant. The novel T5537i mutation was very abundant in tissues from the proband and the infant (>92%) and less abundant (range, 42-89%) in blood, hair follicles, and skin fibroblasts from 4 maternal relatives, 3 of whom showed a neuropsychiatric disturbance. The mutation was not found in more than 100 control subjects. The degree of heteroplasmy in blood correlated well with the severity of the clinical presentation, suggesting specific segregation with the disease.

Adult↗
PubMed1997

Sudden infant death syndrome (SIDS) in a family with myophosphorylase deficiency.

A previously healthy girl died suddenly and unexpectedly at three months of age in her sleep and an autopsy failed to reveal an adequate cause of death. As the father was known to have myophosphorylase (PPL) deficiency (McArdle's disease), we performed molecular genetic analysis of the PPL gene in autopsy muscle of the proposita. The girl was homozygous for the nonsense mutation at codon 49 most commonly associated with typical McArdle's disease. This report suggests that among children presenting as Sudden Infant Death Syndrome (SIDS) there may be cases associated with myophosphorylase deficiency.

Adult↗
PubMed1997

Diagnosis of the mitochondrial encephalomyopathies.

In few fields of medicine has recent progress been as fast and exciting as in the area of mitochondrial diseases. Although the clinical manifestations of mitochondrial dysfunction are extremely variable, biochemical and genetic classification of these disorders is now possible and recent advances in morphologic analysis and genetic testing aid in the identification of patients. What makes these diseases uniquely interesting from a genetic point of view is the fact that mitochondria contain their own DNA, which has distinct genetic properties. It is in the area of mitochondrial DNA defects that there has been extraordinary progress in the past few years, and a new chapter of human genetics, "mitochondrial genetics," has opened up and is becoming increasingly important in the differential diagnosis and in genetic counseling.

DNA, Mitochondrial↗