Biomedical subjects
Publications and source records attributed to S Shanske.
Six glycogen storage diseases (resulting from deficiencies of acid maltase, phosphorylase, phosphofructokinase, phosphoglycerate kinase, phosphoglycerate mutase, and lactate dehydrogenase) and one mitochondrial myopathy (cytochrome c oxidase deficiency) are reviewed to illustrate: clinical heterogeneity, biochemical heterogeneity, evidence for tissue-specific and developmentally controlled isozymes, and molecular genetic studies.
From early childhood, two brothers had mild gait difficulties due to acid maltase deficiency (AMD). Biochemical studies of family members were consistent with autosomal recessive inheritance, but the asymptomatic mother had AM activity in the homozygote range, and her parents had decreased AM activity. The asymptomatic mother may be homozygous for the adult-onset variant of AMD. Alternatively, either the mother or the children may be genetic compounds of the childhood and adult forms of AMD.
Muscle cultures from patients with infantile and later-onset acid maltase deficiency (AMD) and from unaffected controls were studied immunocytochemically with anti-acid maltase (anti-AM) antibodies and fluorescein-labeled goat anti-rabbit IgG second antibody. In control muscle cells, an intense granular distribution of staining was seen, consistent with lysosomal localization of AM. Cultured muscle cells from two patients with infantile AMD (Pompe's disease) did not fluoresce, whereas cells from two patients with AMD of later onset did fluoresce, showing a distribution similar to that of controls.
A 2-month-old boy had progressive generalized weakness, hypotonia, and respiratory insufficiency requiring assisted ventilation. At age 3 1/2 months, he started having seizures and recurrent pulmonary infections; he died at age 7 months. Serum lactate was chronically elevated, but there was no aminoaciduria. Histochemical and ultrastructural studies of muscle biopsies at ages 2 and 3 months showed excessive mitochondria, lipid, and glycogen; a third biopsy at 6 months showed marked increase in perimysial fibrous and fat tissue. Cytochrome c oxidase activity was 7% of normal in the first biopsy and undetectable in the others. Cytochrome spectra of mitochondria isolated from postmortem muscle showed complete lack of cytochrome aa3. Antibodies were obtained against cytochrome c oxidase purified from normal human heart. Immunotitration and enzyme-linked immunosorbent assay (ELISA) showed decreased immunologically reactive enzyme protein in the patient's muscle, but SDS-PAGE electrophoresis of immunoprecipitates of muscle mitochondrial extracts showed the presence of all cytochrome c oxidase subunits. These data suggest that decreased synthesis of one or more subunits may result in markedly decreased concentration of electrophoretically normal complex IV in skeletal muscle.
A new phosphoglycerate kinase variant (PGK New Jersey) has been purified from muscle and cultured fibroblasts of a patient with recurrent myoglobinuria. The mutant enzyme had higher than normal affinity for adenosine triphosphate (ATP) and 3-phosphoglycerate, and a shift of the pH optimum towards the acidic side. Antibodies raised against PGK purified from normal muscle were used to evaluate the presence of immunologically cross-reacting enzyme protein in tissues from the patient. Immunodiffusion and an antibody consumption test showed the presence of reduced amounts of cross-reacting material in the patient's muscle. Several PGK variants have been characterized in asymptomatic individuals or in patients with hemolytic anemia. The biochemical features of PGK New Jersey, the only known variant associated with recurrent myoglobinuria, distinguish this mutant enzyme from others.
The subcellular distribution and isoelectric focusing profile of neutral maltase were investigated in human skeletal muscle from controls and patients with acid maltase deficiency. After subcellular fractionation of normal muscle by differential centrifugation, 75% of the neutral maltase activity was soluble and 13% sedimented with a "microsomal" fraction; the relative specific activity was highest in this latter fraction. After isoelectric focusing (pH gradient 3.5 to 10) of a soluble fraction from control muscle, three peaks of activity were observed: peak 1 had exclusively neutral maltase activity; peak 2 had predominantly neutral maltase activity; and peak 3 had acid maltase activity predominating. The soluble fraction of muscle from a patient with infantile acid maltase deficiency showed no detectable activity at acid pH in any of the peaks and the neutral maltase peaks were unaltered. In muscle from a patient with late-onset acid maltase deficiency the focusing pattern for neutral maltase was similar to controls; the small amount of residual activity at acid pH was found in peak 3.
We studied two brothers with lysosomal glycogen storage disease without acid maltase deficiency in skeletal muscle. Although no specific biochemical defect was identified, a characteristic clinical picture emerged from evaluation of these siblings and two other previously reported patients. The syndrome is manifested by proximal muscle weakness, hypertrophic cardiomyopathy, probable intellectual impairment, and possible liver involvement.
Purification of the dihydrofolate reductases overproduced by 16 independently-derived antifolate-resistant sublines of Chinese hamster lung cells and their drug-sensitive parental cell line, DC-3F, has confirmed our original observation that two molecular weight classes of this enzyme, viz. Mr = 21,000 can be overproduced by drug-resistant cells (Melera, P. W., Wolgemuth, D., Biedler, J. L., and Hession, C. (1980) J. Biol. Chem. 255, 319-322). Of the 16 drug-resistant sublines analyzed, 12 overproduce the 21,000-dalton enzyme, while 4 overproduce the 20,000-dalton enzyme. Both molecular weight classes are found in the drug-sensitive parental line. Two-dimensional polyacrylamide gel electrophoresis of the two molecular weight classes of enzyme has shown that each is composed of two isoelectric forms, and that the relative distributions of the isoelectric forms within a molecular weight class are maintained during overproduction. In vitro translation experiments have demonstrated that the synthesis of these isoelectric forms and their relative distributions are mediated by mRNA. Finally, evidence is presented for the existence of two sets of three dihydrofolate reductase mRNAs in overproducing sublines. Both sets, within a subline, encode the same molecular weight class of dihydrofolate reductase, while each set directs the synthesis of only one of the isoelectric forms within that class. Although the genetic basis for these observations is not yet understood, it is clear that the production of dihydrofolate reductase by Chinese hamster lung cells is complex and probably involves the expression of multiple dihydrofolate reductase genes and/or alleles.
The activities of acid and neutral maltase were measured in lymphocytes, granulocytes, and platelets isolated from controls and from 5 patients with late-onset acid maltase deficiency (AMD). Lymphocytes from patients had markedly decreased activity of acid maltase and elevated neutral/acid ratios. In granulocytes, acid maltase was also lower than in controls, but significant activity was retained at pH 4: neutral/acid ratios were consistently elevated. Normal platelets had low acid and high neutral maltase activities: both enzyme activities varied within wide ranges and patients could not be distinguished from controls. The variable proportion of different cell types in unfractionated leukocyte preparations may yield unreliable values when used for detection of AMD. However, lymphocytes isolated from 20 ml of blood provide a readily accessible and reliable source of tissue for accurate diagnosis.
Muscle cultures from a patient with I-cell disease showed the characteristic morphologic and biochemical abnormalities previously observed in cultured fibroblasts. At early stages of myoblast growth, there were numerous inclusions. Biochemically, the intracellular activities of beta-galactosidase, beta-hexosaminidase, and alpha-mannosidase were reduced to 1, 14, and 5%, respectively, of control values, and this was accompanied by elevated levels of beta-hexosaminidase and alpha-mannosidase in the culture medium. Cultures from the patient did not fuse as well as controls; however, when well-developed myotubes possessing distinct cross-striations were present, these no longer had inclusions. In the muscle biopsy from this patient, only beta-galactosidase was decreased to approximately 50% of the mean control value whereas beta-hexosaminidase and alpha-mannosidase activities were increased as compared to controls. These data suggest that the I-cell mutation is expressed during early myogenesis but not in well-differentiated myotubes or mature muscle fibers.
It has been previously shown by morphological techniques and measurements of lysosomal enzyme levels that the I cell mutation is expressed in myoblasts but not in myotubes or mature muscle fibers. These findings suggested the possibility of developmental regulation of the affected enzyme, UDP-N-acetylglucosamine: lysosomal enzyme N-acetylglucosamine-phosphotransferase. In this article, we examine this possibility by measuring the phosphotransferase activity at various stages of muscle differentiation in three different animal species (human, chick, rat). Although activity of the enzyme is consistently higher in myoblasts than in myotubes or mature muscle, the difference in the levels of activity at these three states of muscle differentiation varies widely in the three species examined. We further found that the phosphotransferase activity was absent in the muscle of an I cell patient, in spite of normal muscle morphology. This indicates the presence of a mannose-6-phosphate-independent mechanism for lysosomal enzyme targeting in muscle and other unaffected tissues. The existence of such a pathway cannot be explained by lack of the necessary enzyme, as the phosphotransferase is present at a comparable level in normal muscle of three different species (human, chick, rat).
Disorders associated with mitochondrial DNA (mtDNA) mutations are usually dominated by involvement of the nervous system and skeletal muscle (hence the term "mitochondrial encephalomyopathies"). However, considering the high dependence of the heart on oxidative metabolism, it is not surprising that myocardial dysfunction is often a prominent feature in these disorders, either as isolated cardiomyopathy or as part of a multisystem mitochondrial syndrome. We report an infant with a maternally inherited C-to-T transition at nucleotide 3303 of mtDNA in the tRNA(Leu(UUR)) gene; this is the second kindred with cardiomyopathy identified to have this mutation of mitochondrial DNA. A brief review of other mitochondrial DNA defects is also included.
We report a family in which a mother and son were affected with diabetes mellitus and myopathy characterized by ragged red fibers and suggestive of mitochondrial disease. Mitochondrial DNA (mtDNA) analysis of DNA isolated from peripheral blood showed a T-->C point mutation at nucleotide position 14709, in the transfer RNA gene for glutamic acid. We review the association of diabetes and mtDNA mutations. This child's case is unusual because of the early onset of diabetes, which is more typical of mtDNA deletions.