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J M Shoffner

Publications and source records attributed to J M Shoffner.

49 records · Page 3Linked to original sources
PubMed1991

Hypoxemia is associated with mitochondrial DNA damage and gene induction. Implications for cardiac disease.

OBJECTIVE: --Oxidative phosphorylation (OXPHOS) deficiency due to hypoxemia or other causes was hypothesized to increase oxygen radical generation, damage mitochondrial DNA (mtDNA), and reduce adenosine triphosphate synthesis, resulting in compensatory OXPHOS gene induction. Therefore, we investigated the levels of mtDNA damage and OXPHOS transcripts in normal and ischemic hearts, and then in other forms of heart disease. DESIGN: --DNA was extracted from the heart and the levels of the common 4977 base pair mtDNA deletion were quantitated as an index for mtDNA damage. Total RNA was extracted from hearts and analyzed for OXPHOS transcript levels. RESULTS: --In control hearts, the 4977 base pair mtDNA deletion appeared at age 40 years and reached a maximum deletion of 0.0035%. Much higher levels were found in ischemic hearts (0.02% to 0.85%), as well as in three of 10 cases with other types of heart disease (0.017% to 0.16%). The OXPHOS transcripts were increased in all diseased hearts. CONCLUSION: --Ischemic hearts have increased mtDNA damage and OXPHOS gene expression, suggesting that mtDNA damage is associated with OXPHOS deficiency. Oxidative phosphorylation defects may also play a role in some other forms of cardiac disease.

Adenosine Triphosphate↗
PubMed1991

Mitochondrial oxidative phosphorylation defects in Parkinson's disease.

Parkinson's disease has been associated with defects in oxidative phosphorylation (Oxphos). We analyzed mitochondria isolated from muscle biopsies of 6 patients with Parkinson's disease for deficiencies in Oxphos enzymes and for mutations in the mitochondrial DNA. Oxphos enzyme assays were compared to the 5 to 95% confidence intervals from 16 control subjects. Four patients had complex I defects, whereas 1 patient had a complex IV defect. A genetic basis for Parkinson's disease was suggested by the presence of affected relatives of 2 patients with Parkinson's disease. Known pathological mitochondrial DNA mutations (insertion-deletions or point mutations) were not found. We conclude that Parkinson's disease is a systemic disorder of Oxphos, probably of a complex genetic etiology. Premature cell death in the nigrostriatal dopamine pathway could be due to energetic impairment and accentuated free radical generation caused by an Oxphos defect.

Adult↗
PubMed1991

MERRF: a model disease for understanding the principles of mitochondrial genetics.

The principles of mitochondrial genetics have evolved over the past 20 years. Careful identification of large pedigrees that were consistent with maternal inheritance has permitted detailed clinical and genetic investigations. Myoclonic epilepsy and ragged-red fiber (MERRF) disease has been a model disease for the application of these principles. MERRF is caused by an A to G mutation of the mitochondrial tRNA(Lys) at position 8344. The mutation is maternally inherited and heteroplasmic. Disease manifestations are dependent on replicative segregation of mutant and wild type mitochondrial DNAs and on the threshold effect. Characterization of the clinical, physiological, biochemical, and genetic manifestations of this disease has provided a better understanding of how to diagnose and manage oxidative phosphorylation diseases which are caused by mutations in the mitochondrial DNA.

Base Sequence↗
PubMed1990

Evaluation of procedures for assaying oxidative phosphorylation enzyme activities in mitochondrial myopathy muscle biopsies.

The mitochondrial myopathies (MM) are a heterogenous group of neuromuscular diseases associated with abnormal mitochondria and defects in mitochondrial oxidative phosphorylation (OXPHOS). Analysis of a broad spectrum of MM patients has revealed that patients with similar clinical symptoms frequently do not have the same muscle OXPHOS defect. To determine whether some of this variation was due to methodological differences between studies, we have made a detailed survey of OXPHOS enzyme analysis procedures. The coupled OXPHOS assays for Complexes I + III and II + III were found to be variable due to competing reactions and complicated interactions between complexes. These problems were resolved by utilizing specific Complex I and III assays. The muscle mitochondria isolated from surgery patients under general anesthesia and prepared by proteinase digestion were observed to give low and highly variable OXPHOS activities. Mitochondria isolated from muscle biopsies performed under local anesthesia and finely sliced prior to homogenization gave higher and more consistent OXPHOS activities. Assays for Complexes I, III and V required mitochondrial sonication to express maximal activity, but Complex IV was prone to inactivation by excessive mechanical disruption. Mitochondria isolated from frozen muscle or from patients with an OXPHOS disease are more fragile than those isolated from fresh tissue and normal individuals. Hence, Complex IV activity can be preferentially lost from frozen and sonicated myopathy patient samples. These results suggest that variation in muscle OXPHOS analysis techniques may account for some of the discrepancies between clinical manifestations and OXPHOS defects and suggest that no single protocol is sufficient to adequately define the OXPHOS defect in MM patients.

Biopsy↗
PubMed1990

Myoclonic epilepsy and ragged-red fiber disease (MERRF) is associated with a mitochondrial DNA tRNA(Lys) mutation.

An A to G transition mutation at nucleotide pair 8344 in human mitochondrial DNA (mtDNA) has been identified as the cause of MERRF. The mutation alters the T psi C loop of the tRNA(Lys) gene and creates a CviJI restriction site, providing a simple molecular diagnostic test for the disease. This mutation was present in three independent MERRF pedigrees and absent in 75 controls, altered a conserved nucleotide, and was heteroplasmic. All MERRF patients and their less-affected maternal relatives had between 2% and 27% wild-type mtDNAs and showed an age-related association between genotype and phenotype. This suggests that a small percentage of normal mtDNAs has a large protective effect on phenotype. This mutation provides molecular confirmation that some forms of epilepsy are the result of deficiencies in mitochondrial energy production.

Adenine↗
PubMed1990

Mitochondrial DNA mutations associated with neuromuscular diseases: analysis and diagnosis using the polymerase chain reaction.

A number of neuromuscular diseases are associated with molecular defects in the mitochondrial DNA (mtDNA). These include: 1) a missense mutation at nucleotide 11778 in the mtDNA of Leber's hereditary optic neuropathy patients; 2) a heterogeneous array of deletions in the mtDNA of ocular myopathy patients; and 3) small deletions and point mutations in the mtDNA of myoclonic epilepsy and ragged red fiber disease patients. We can now diagnose these diseases at the molecular level from small patient samples by amplifying the affected mtDNA regions using the polymerase chain reaction. Leber's hereditary optic neuropathy is diagnosed through loss of an SfaNI restriction site. Ocular myopathy deletions are identified by differential amplification across deletion breakpoints. Familial diseases such as myoclonic epilepsy and ragged red fiber disease might be diagnosed by identifying small deletions through amplification and electrophoretic analysis of the entire mtDNA genome or by identifying point mutations through differential oligonucleotide hybridization. As additional mtDNA molecular defects are identified, molecular analysis will likely become a primary tool for the diagnosis of these diseases.

Base Sequence↗
PubMed1989

Spontaneous Kearns-Sayre/chronic external ophthalmoplegia plus syndrome associated with a mitochondrial DNA deletion: a slip-replication model and metabolic therapy.

The muscle mitochondria of a patient with Kearns-Sayre/chronic external ophthalmoplegia plus syndrome were found to be completely deficient in respiratory complex I activity and partially deficient in complex IV and V activities. Treatment of the patient with coenzyme Q10 and succinate resulted in clinical improvement of respiratory function, consistent with the respiratory deficiencies. Restriction enzyme analysis of the muscle mtDNA revealed a 4.9-kilobase deletion in 50% of the mtDNA molecules. Polymerase chain reaction analysis demonstrated that the deletion was present in the patient's muscle but not in her lymphocytes or platelets. Furthermore, the deletion was not present in the muscle or platelets of two sisters. Hence, the mutation probably occurred in the patient's somatic cells. Direct sequencing of polymerase chain reaction-amplified DNA revealed a 4977-base-pair deletion removing four genes for subunits of complex I, one gene for complex IV, two genes for complex V, and five genes for tRNAs, which paralleled the respiratory enzymes affected in the disease. A 13-base-pair direct repeat was observed upstream from both breakpoints. Relative to the direction of heavy-strand replication, the first repeat was retained and the second repeat was deleted, suggesting a slip-replication mechanism. Sequence analysis of the human mtDNA revealed many direct repeats of 10 base pairs or greater, indicating that this mechanism could account for other reported deletions. We postulate that the prevalence of direct repeats in the mtDNA is a consequence of the guanine-cytosine bias of the heavy and light strands.

Base Sequence↗
PubMed1989

Evidence in a lethal infantile mitochondrial disease for a nuclear mutation affecting respiratory complexes I and IV.

A child died at 4 months of age of a lethal infantile mitochondrial disease associated with cardiomyopathy. Detailed pathologic evaluation of this patient revealed abnormalities in the striated muscle, smooth muscle, heart, and liver, but not the central nervous system. Biochemical analysis revealed a combined complex I and IV deficiency in skeletal muscle, heart, and liver, but not in kidney and brain. Analysis of mitochondrial translation products and mitochondrial DNA failed to detect any abnormality. Parallel studies on both parents were uniformly normal. These data support the hypothesis that this disease was the result of a nuclear DNA mutation in a developmental stage-specific and tissue-specific oxidative phosphorylation-gene.

Cardiomyopathies↗
PubMed1988

Familial mitochondrial encephalomyopathy (MERRF): genetic, pathophysiological, and biochemical characterization of a mitochondrial DNA disease.

A large MERRF pedigree permitted the direct testing of the predictions for a mitochondrial DNA (mtDNA) mutation. A mtDNA mutation was demonstrated by proving maternal inheritance and by identifying specific deficiencies in muscle energetics and mitochondrial respiratory complexes I and IV. mtDNA heteroplasmy (a mixture of mutant and wild-type mtDNAs) was demonstrated by showing variation in the mitochondrial energetic capacity between family members. The phenotypic consequences of differential tissue-specific reliance on mitochondrial ATP was shown by correlating individual respiratory deficiency with the nature and severity of patients' clinical manifestations. The observed spectrum of clinical manifestations resulting from this heteroplasmic mtDNA mutation implies that mtDNA disease may be much more prevalent than previously anticipated.

Calorimetry, Indirect↗
PubMed1985

Human growth hormone gene deletion without antibody formation or growth arrest during treatment--a new disease entity?

Using restriction endonuclease analysis of genomic DNA hybridized to a human chorionic somatomammotropin (hCS) complementary (c)DNA probe, we studied four young Jewish patients with isolated growth hormone deficiency (IGHD), and 15 family members. One family originated in Iraq, two in Yemen and one in Iran. Each patient was homozygous for a deletion of approximately 7.5 kilobases, which included the hGH-N gene. Three of the deletions were associated with the same restriction fragment length polymorphism haplotype, while the deletion in the child of Iranian descent was associated with a different haplotype. All the patients were treated with three injections per week of pituitary human growth hormone (hGH) for periods of 2 1/2 to 14 1/2 years. All had a good growth response. Three reached normal and one almost normal height. Repeated serum analyses revealed absence of anti-hGH antibodies. Thus, the presently described patients differ from those previously reported from Switzerland, Argentina and Japan, all of whom developed anti-hGH antibodies during treatment, with resultant slowing or arresting of growth. Expression of heterozygosity in family members was variable with regard to stature, hGH reserve and insulin-like growth factor I (IGF-I) levels. It is hypothesized that hGH-N gene deletion is not the sole determinant of immune response during hGH treatment, and that the difference between the current series and other cases needs further investigation.

Autoantibodies↗