Desensitization of two young patients with infantile-onset Pompe disease and severe reactions to alglucosidase alfa.

Pompe disease is a metabolic myopathy, due to deficiency of alpha glucosidase, with a wide clinical spectrum. Enzyme replacement therapy is the only available treatment to improve morbidity and mortality, especially in infantile-onset form. However, some patients experience infusion-associated reactions, which may restrict their access to this treatment. We report on two patients (respectively 12 and 3 months old) with infantile-onset Pompe disease and severe cardiomyopathy, that presented with severe reactions during infusion of enzyme replacement therapy and were successfully desensitized with a new individualized protocol. Our protocol, using microdilution and a premedication with antihistamines, corticosteroids, and tranexamic acid, seems safe and effective and it may allow the continuation of therapy in Pompe patients resulting in the reduction of morbidity and mortality related to this disease.

Steroid therapy in an alpha-dystroglycanopathy due to GMPPB gene mutations: A case report.

Alpha-dystroglycanopathies are a group of progressive and untreatable neuromuscular disorders, due to aberrant alpha-dystroglycan glycosylation. We describe the effects of a short-term cycle of corticosteroid therapy in a 9-year-old boy, affected by an alpha-dystroglycanopathy due to GMPPB gene mutations. The patient was affected by a congenital progressive muscular dystrophy since the first month of life, associated with psychomotor delay, seizures, and congenital bilateral cataracts. Despite physical therapy he had a progressive motor impairment. At the age of 9 years, he was treated with 0.75 mg/kg/day of prednisone for 3 months and showed improvements in muscle strength and function scores and creatine kinase reduction. When steroid therapy was discontinued he showed again clinical and biochemical deterioration. These data suggest that corticosteroid may be considered as a treatment for patients with alpha-dystroglycanopathies due to GMPPB mutations.

Deficiency of 5'-deoxy-5'-methylthioadenosine phosphorylase activity in malignancy. Absence of the protein in human enzyme-deficient cell lines.

The absence of 5'-deoxy-5'-methylthioadenosine phosphorylase (MTAase) activity in malignant cells, and the putative localization of its gene, suggest that this enzyme deficiency might be due to a genomic alteration also involving a tumour-suppressor gene. We studied the possible occurrence of inactive forms of the protein in two MTAase-negative cell lines, namely K562 and Jurkat, by immunochemical methods. Two highly specific antisera, directed against different epitopes of the phosphorylase [Della Ragione, Oliva, Gragnaniello, Russo, Palumbo & Zappia (1990) J. Biol. Chem. 265, 6241-6246], were used to carry out immunotitration and immunoblotting analyses, as well as to investigate the biosynthesis of the enzyme. No MTAase protein was detected by Western-blotting technique performed under conditions where all the phosphorylase-positive samples gave a clear band at the MTAase subunit molecular mass. No cross-reacting material was observed by a sensitive immunotitration method which permitted the detection of as low as 0.5 ng of protein. Moreover, the results obtained by [35S]methionine-labelling experiments ruled out phosphorylase biosynthesis in the negative cell lines. Altogether, these data suggest that an alteration at the gene level hampering the specific mRNA biosynthesis or resulting in an untranslatable mRNA is the cause of the enzyme deficiency in the MTAase-negative cell lines studied.

Physicochemical and immunological studies on mammalian 5'-deoxy-5'-methylthioadenosine phosphorylase.

5'-Deoxy-5'-methylthioadenosine phosphorylase (MTAase) was purified to homogeneity (10,000-fold) from bovine liver with a recovery of 12%. The pure protein shows a molecular weight of about 98,000 +/- 3,000 and is composed of three apparently identical subunits. Several physicochemical features have been investigated including hydrodynamic properties, amino acid composition, and secondary structure. In particular, the CD spectrum of the protein indicates a very low alpha-helical content and a large percent of beta-structure and random coil. The pure protein was used to raise specific rabbit antisera but, because of the scarce antigenic properties of the native enzyme, different chemically modified forms were prepared and employed as immunogens. Among the antibodies obtained, those to keyhole limpet hemocyanin-MTAase recognize both the native and the denatured enzyme and are also active against the human protein. Therefore, they were employed as a tool to investigate the occurrence of inactive forms of MTAase in two human malignant cell lines lacking this enzymatic activity. The results obtained with K562 and Jurkat cells indicate that the protein is absent in these phosphorylase-deficient cell lines.

Chromatographic and radioimmunological methods for the determination of 5'-deoxy-5'-methylthioadenosine in biological fluids.

Two specific methods for the determination of 5'-deoxy-5'-methylthioadenosine (MTA) in biological samples have been developed. The chromatographic procedure requires a preliminary step on a phenylboronate column to remove non-cis-diol compounds. The sample is then analysed using a high-performance liquid chromatography system equipped with a reversed-phase column. 5'-Deoxy-5'-methyl-thio[2-3H]adenosine with high specific activity was synthesized and employed as an internal standard. An alternative radioimmunoassay (RIA) procedure has also been developed. The RIA method is based on competition between the unlabelled thio-ether and 3H-labelled MTA for the binding to a specific antiserum. Anti-MTA antibodies were obtained from rabbits immunized with the nucleoside covalently linked to carrier proteins. Both the chromatographic and RIA procedures gave identical results when employed to determine MTA in human urine.

Purification and characterization of 5'-deoxy-5'-methylthioadenosine phosphorylase from human placenta.

5'-Methylthioadenosine phosphorylase has been purified to homogeneity (30,000-fold) from human full-term placenta by a procedure involving covalent chromatography on organomercurial-agarose as the major step. The specific activity of the homogeneous enzyme is 10.2 mumol of 5'-methylthioadenosine cleaved per min per mg of protein, and the overall yield is about 20%. The enzyme has a molecular weight of 98,000, as determined by gel filtration on Sephacryl S-200 and Superose 6B, and is composed by three apparently identical subunits with a molecular weight of 32,500. The isoelectric point is 5.5, and the optimal pH ranges from 7.2 to 7.6. The resistance of the enzyme to thermal inactivation is increased remarkably by the addition of 5'-methylthioadenosine or phosphate. The homogeneous enzyme shows an absolute requirement for -SH-reducing agents and is specifically and rapidly inactivated by thiol-blocking compounds. The reaction catalyzed by the enzyme is fully reversible with a Keq of 1.39 X 10(-2) (in the direction of phosphorolysis) at 37 degrees C and pH 7.4. The Km values for 5'-methylthioadenosine, phosphate, adenine, and 5-methylthioribose 1-phosphate are 5, 320, 23, and 8 microM, respectively.

Increased methyl esterification of membrane proteins in aged red-blood cells. Preferential esterification of ankyrin and band-4.1 cytoskeletal proteins.

The enzymatic carboxyl methyl esterification of erythrocyte membrane proteins has been investigated in three different age-related fractions of human erythrocytes. When erythrocytes of different mean age, separated by density gradient centrifugation, were incubated under physiological conditions (pH 7.4, 37 degrees C) in the presence of L-[methyl-3H]methionine, the precursor in vivo of the methyl donor S-adenosylmethionine, a fourfold increase in membrane-protein carboxyl methylation was observed in the oldest cells compared with the youngest ones. The identification of methylated species, based on comigration of radioactivity with proteins stained with Coomassie blue, analyzed by sodium dodecyl sulfate/polyacrylamide gel electrophoresis, shows, in all cell fractions, a pattern similar to that reported for unfractionated erythrocytes. However in the membrane of the oldest erythrocytes the increase in methylation of the cytoskeletal proteins, bands 2.1 and 4.1, appears to be significantly more marked compared with that observed in the other methylated polypeptides. Furthermore the turnover rate of incorporated [3H]methyl groups in the membrane proteins of the oldest cells markedly increases during cell ageing. Particularly in band 4.1 the age-related increase in methyl esterification is accompanied by a significant reduction of the half-life of methyl esters. The activity of cytoplasmic protein methylase II does not change during cell ageing, while the isolated ghosts from erythrocytes of different age show an age-related increased ability to act as methyl-accepting substrates, when incubated in presence of purified protein methylase II and methyl-labelled S-adenosylmethionine, therefore the relevance of membrane structure in determining membrane protein methylation levels can be postulated. Finally the possible correlation of this posttranslational protein modification with erythrocyte ageing is discussed.