Neurologic syndromes in hyperammonemic disorders

This article reviews the neurologic manifestations of hyperammonemic disorders. A variety of inborn errors of metabolism, as well as transient neonatal or acquired hepatic dysfunctions, are identified as causes of hyperammonemia. The pathogenesis of hyperammonemia in these disorders is outlined. Catastrophic hyperammonemia and hyperammonemic coma are described; algorithms to establish specific diagnosis are suggested. Symptoms of less severe ammonia intoxication, which also occur in more common diseases, are described. The need to consider hyperammonemia as a potential etiology for these symptoms is emphasized. Finally, the neurotoxicity of ammonia is discussed.

The application of bone marrow transplantation to the treatment of genetic diseases

Genetic diseases can be treated by transplantation of either normal allogeneic bone marrow or, potentially, autologous bone marrow into which the normal gene has been inserted in vitro (gene therapy). Histocompatible allogeneic bone marrow transplantation is used for the treatment of genetic diseases whose clinical expression is restricted to lymphoid or hematopoietic cells. The therapeutic role of bone marrow transplantation in the treatment of generalized genetic diseases, especially those affecting the central nervous system, is under investigation. The response of a generalized genetic disease to allogeneic bone marrow transplantation may be predicted by experiments in vitro. Gene therapy can be used only when the gene responsible for the disease has been characterized. Success of gene therapy for a specific genetic disease may be predicted by its clinical response to allogeneic bone marrow transplantation.

[Lipid storage diseases (lipidoses): genetic, biochemical and clinico-chemical aspects]

Lipidoses are genetic diseases due to disease-specific defects in the enzymatic catabolism of lipids, with accumulation of the respective lipid substrate in the nervous system and/or peripheral tissues. The clinical chemical diagnosis of lipidoses can be accomplished by demonstration of the enzyme defect and/or substrate accumulation in body fluids (urine, blood serum), leukocytes, cultured fibroblasts, amniotic fluid cells, or amniotic fluid, respectively. These assays are important with regard to: 1. the specific detection or exclusion of diseases, which are difficult to diagnose by their clinical presentation, 2. prenatal diagnoses, 3. detection of (clinically inconspicuous) heterozygotes (essential for individual genetic counselling), and 4. the biochemical control of dietary treatment in Refsum's disease.

Judging health status: Effects of perceived prevalence and personal relevance

In this article, we show that people's evaluations of the seriousness of a health disorder are influenced by the perceived prevalence and personal relevance of that disorder. As part of a study ostensibly concerned with college students' health characteristics, 60 undergraduates were "tested" for the presence of a fictitious enzyme deficiency. The subjects discovered either that they had the deficiency (deficiency-present subjects) or that they did not have it (deficiency-absent subjects), and were led to believe either that 1 of the 5 people in the laboratory had the deficiency (low-prevalence subjects) or that 4 of them had it (high-prevalence subjects). As predicted, the low-prevalence subjects evaluated the deficiency as more serious than did the high-prevalence subjects. In addition, consistent with the view that personal relevance affects perceptions of health disorders, the deficiency-present subjects evaluated the deficiency as less serious than did the deficiency-absent subjects. The deficiency-present subjects also derogated the validity of the test ostensibly used to diagnose the deficiency compared with other subjects. Finally, the deficiency-present subjects requested more information about the deficiency than did the deficiency-absent subjects.

Myopathies due to enzyme deficiencies

After the discovery in 1959 of myophosphorylase deficiency, at least 15 myopathies due to deficiency of enzymes involved in energy substrate utilization have been described. In this review two main categories of enzymopathies, glycogenosis and mitochondrial disorders, are discussed. Clinically, the patients with these categories of enzyme defects present two major syndromes: acute recurrent muscle impairment, generally related to exercise, associated with cramps and/or myoglobinuria; progressive muscular weakness and wasting eventually associated with signs of affected organs other than skeletal muscle. Defects of glycogen breakdown and of the first step of glycolysis are more frequently associated with acute exercise intolerance, such as in myophosphorylase and phosphofructokinase deficiencies, but may be associated with progressive muscle weakness and wasting, such as in acid maltase and debrancher enzyme deficiency. Clinical heterogeneity is common in these disorders, but a biochemical explanation for their different clinical expression is still lacking. Defects of the second step of glycolysis, phosphoglycerate kinase, phosphoglycerate mutase and lactate dehydrogenase deficiencies, have been discovered recently and are associated with exercise intolerance. The reason for muscle weakness and atrophy in glycogenosis is still unclear, although it has been suggested that excessive protein catabolism occurs in myophosphorylase, debrancher and acid maltase deficiencies. Myopathies due to deficiencies of mitochondrial enzymes are less well defined, as a group, than the glycogenoses. They are currently considered to fall into three main groups: defects of substrate utilization, such as carnitine palmitoyltransferase deficiency; defects of respiratory chain complexes, such as cytochrome-c-oxidase deficiency and defects of phosphorylation-respiration coupling, such as Luft's disease. Again, severe and benign exercise intolerance or progressive life-threatening myopathic syndromes may be the clinical expression of these disorders. Detailed biochemical and morphological studies of muscle biopsies are needed in these patients to obtain a definite diagnosis and prognosis, and to decide on eventual treatment.

[Mitochondrial myopathies and encephalomyopathies. Neuromuscular and central nervous system diseases caused by defects in mitochondrial oxidative metabolism]

In this review the clinical data and biochemical findings of disorders of oxidative metabolism in the mitochondria are summarized. Defects in pyruvate metabolism, the citric acid circle, the respiratory chain and less well defined disorders of energy transfer are discussed.

Age dependent behaviour of red cell glycolytic enzymes in haematological disorders

The age dependent behaviour of 11, mainly glycolytic, red blood cell enzymes in 26 patients with various haematological disorders has been investigated after separation of red blood cells by discontinuous density gradient centrifugation. The frequency of enzyme deficiencies in the old cells of these patients was significantly increased in comparison with the unseparated cells, 29 and 13 deficiencies, respectively. Particularly hexokinase activity, although normal or even increased in unseparated cells, was found deficient in old cells in seven cases. In addition, an increased number of phosphofructokinase deficiencies was observed in the patients' old cells (eight cases) as compared to the unseparated cells (three cases). However, the red blood cells of the majority of these patients were found to contain increased enzyme activities, irrespective of cell age. Enzyme activities in the youngest cell population did not correlate with the reticulocyte count. Cases of high pyruvate kinase and hexokinase activities were studied for kinetical, electrophoretical and immunological properties of the respective enzymes, but no abnormalities could be demonstrated, indicating an increased synthesis of these enzymes.

Molecular aspects of erythroenzymopathies associated with hereditary hemolytic anemia

Since the discovery of glucose 6-phosphate dehydrogenase (G6PD) and of pyruvate kinase deficiencies, erythroenzymopathies associated with hereditary hemolytic anemia have been extensively investigated. Kinetic and electrophoretic studies have shown that most, if not all, erythroenzymopathies are caused by the production of a mutant enzyme. Except for a few enzymes that are abundant in blood and tissues, it is difficult to obtain enough sample to study the functional and structural abnormalities of mutant enzymes associated with genetic disorders in man. The primary structures of only two normal red cell enzymes which can cause hereditary hemolytic anemia, phosphoglycerate kinase (PGK) and adenylate kinase, have been determined. Single amino acid substitutions of PGK variants have been found, and the identification of the exact molecular abnormalities of such variants has helped us to understand the accompanying functional abnormality. Gene cloning makes possible the identification of the DNA sequence that codes for enzyme proteins. Recently, human complementary DNA (cDNA) for aldolase, PGK, G6PD, and adenosine deaminase (ADA) have been isolated, and the nucleotide sequences for PGK and ADA determined. In the near future, human cDNA sequencing should permit identification of the gene alteration that gives rise to the mutant enzymes.

A method for enrichment of hybrid somatic cells: complementation studies in certain lysosomal enzymopathies

An improved method, which combined a number of published techniques, is described for the polyethylene-glycol-induced fusion of mononuclear human skin fibroblasts in the presence of phytohaemagglutinin-P and for the subsequent isolation of polynuclear cells by Ficoll gradient sedimentation. Enriched cultures contain between 60 and 75% multinucleated cells and may be maintained in culture without fetal calf serum for up to 14 days without significant overgrowth by the few contaminating mononuclear parental cells. Complementation appears not to occur between GM1 gangliosidosis and mucopolysaccharidosis, type VI B (Morquio) cell strains; this experimental observation provides support for the earlier hypothesis that the mutations for these conditions are allelic. Earlier observations that complementation does not occur between selected phenotypic variants (viz., neuronopathic forms and those without neurological involvement) of sphingomyelin storage (Niemann-Pick) disease or Gaucher's disease are confirmed.

Enzymatic deficiencies of the immune system cells in patients with cancer of the larynx and other malignancies

Activity of N-acetyl-beta-D-glucosaminidase, beta-glucuronidase, and acid phosphatase and myeloperoxidase was determined in neutrophils and lymphocytes of patients with cancer of the larynx and precancerous states of the larynx as well as--for comparative reasons--in patients with malignant tumors of female generation organs, breast carcinoma, cancer of the stomach and endometriosis. The main result of investigations performed was in fact that intracellular deficiency of beta-glucuronidase within the neutrophils characterizes patients with cancer and precancerous states of the larynx. Patients with cancer of the larynx show additionally a deficiency of neutrophil myeloperoxidase. Deficiency of N-acetyl-beta-D-glucosaminidase occurs, in contrast, in patients with malignancies of female generation organ. Activity of myeloperoxidase in neutrophils from patients with gastric carcinoma is slightly elevated.

The fate of pharmaceutical chemicals in the aquatic environment

Increased demands for potable water, especially where supplies are drawn from lowland rivers has necessitated a greater degree of water re-use. As water undertakings have a duty to maintain the wholesome quality of potable water supplies, increasing concern is being expressed over the presence of organic micro-contaminants (contaminants found at microgram litre-1 concentrations). This study outlines some of the problems encountered in assessing the risk from pharmaceutical chemicals which might enter the water cycle from domestic and industrial sources. Analytical chemistry was of value for only a few of the 200 compounds studied. However, much useful information was derived from the human metabolic routes of the drugs and is collated in Appendix I. Biodegradation studies and other ecotoxicity/environmental toxicology data may be required to a greater extent in the future. Particular consideration is given to vulnerable sections of the population.

Enzymes and survival

Age related deficits in enzyme systems, such as those which control lipid metabolism and hence provoke cardiovascular pathologies, can be reversed by replacement therapy either by-passing the enzyme by supplying the product of its reaction or by administering the enzyme itself. There are difficulties associated with enzyme therapy associated with their high molecular weight and protein reactions. Our enzyme preparation which has been shown to be effective in modifying plasma lipid profiles in atherosclerotics, is Vasolastine. Following intramuscular administration of elderly subjects it reduces the circulating cholesterol in the 75-80 age group by 13% but at the extremes of the age range (60-75 and 80-95) increases the level by between 1.5% and 5.0%. HDL-cholesterol levels, however, are raised by 5% over the whole age range. The effect of these changes is to lower the ratio of total plasma cholesterol to HDL-cholesterol at all ages up to the end of the 9th decade by approximately 6%, whereas at ages above 80 years the enzyme preparation lowers the value of the ratio by less than 3%. Since high values of this ratio correlate with a high risk of coronary disease, it may be inferred that over the lower part of this elderly age range Vasolastine reduces the risk, whereas at higher ages when the risk in untreated subjects is lower, the protective effect of the enzyme preparation is less pronounced.

Non-equilibrium thermodynamics and degenerate disease

Non-equilibrium thermodynamics, biochemistry and physiology can be associated to form a possible foundation for a theory of nutritional medicine. The theory predicts a new class of diseases. The relationship between this new class and cancer is discussed.

Prenatal diagnosis of the organic acidurias

Prenatal diagnosis for the genetic counselling of families at risk for having children with the life-threatening organic acidurias is advancing rapidly. The two major approaches to prenatal diagnosis are the assay for deficient activity of the enzymes in cultured amniocytes and the measurement of increased concentrations of the organic acids in the amniotic fluid. The latter, when done by stable isotope dilution analysis, is rapid, relatively inexpensive and very reliable.

The frequency among Japanese of heterozygotes for deficiency variants of 11 enzymes

Eleven human enzymes, chosen for this study because of relatively small coefficients of variation for mean activity, have been surveyed for the frequency with which activities less than or equal to 66% of the mean value occur. This criterion should detect almost all heterozygotes for variants lacking any activity plus a fraction of the persons with variants characterized by markedly depressed activity and/or instability. The enzymes surveyed are TPI, PGK, AK1, LDH, GAPD, GPI, PK, 6PGD, G6PD, GOT1, and HK. The number of determinations per enzyme ranged from 310 to 3,173, for a total of 26,634 determinations. Family studies have thus far been possible in 52 instances in which the initial observation of activity less than or equal to 66% of normal was confirmed. In every instance, a parent exhibited a similar finding, giving confidence that a true genetic entity was being detected. With this approach, the frequency of heterozygotes per 1,000 determinations varied from 0.0 (AK1, 6PGD) to 13.8 (PK), with an average of 2.4. For these same systems, in this laboratory the frequency of "rare" electrophoretic variants is 2.3/1,000, the ratio of the latter to the former thus being 1.0 in Japanese. Our experience with these deficiency phenotypes to date suggests that for selected enzymes such phenotypes can be incorporated into a program designed to detect mutational events.

Selectivity of proteases as a basis for tissue distribution of enzymes in hereditary deficiencies

In hereditary deficiencies of glucose-6-phosphate dehydrogenase and of a number of other enzymes, there are marked differences in the extent to which various tissues manifest the deficiency state. I propose that such anomalous distribution of enzyme activity can be explained by tissue-to-tissue differences in proteases. Mutations that render an enzyme susceptible to proteolytic destruction in some tissues may produce molecular changes that are not recognized in others. This interpretation is consistent with a number of known properties of proteases and of mutant enzymes, and it has implications regarding the diagnosis of various enzyme deficiency states.