Biomedical subjects
Publications and source records attributed to R A Kark.
Explore the source record for details and available documents.
To study the incidence of abnormalities of the pyruvate (PDH) or ketoglutarate (KGDH) dehydrogenase complexes in patients with spinocerebellar degenerations, we measured the activities of PDH and KGDH in platelet-enriched preparations from the blood of 14 patients. Low PDH was found in 6 of the 14 patients; low KGDH was found in 2 of the 6. PDH-normal and PDH-abnormal patients could not be distinguished by clinical criteria. These results extend previous studies, which suggested abnormalities of pyruvate oxidation in patients with hereditary ataxias. The data imply that deficient activity of the PDH complex may be associated with spinocerebellar degenerations, and that the clinical phenotypes of the inherited ataxias can be associated with several genotypes.
Reduced activities of lipoamide dehydrogenase (LAD) relative to cytochrome oxidase have been found in 12 or 26 patients with inherited ataxias. One of the 12 patients had adult-onset ataxia plus ragged-red muscle fibers. The other 11 had Friedreich syndrome or early-onset variants of this, as did 6 patients with normal enzyme activity. However, the 11 patients with reduced enzyme activity were clinically more homogeneous than the 6 with normal activity.
Explore the source record for details and available documents.
Three new cases of carnitine palmityl transferase deficiency are described. The syndrome consists of recurrent attacks of muscle cramps, weakness, malaise, and myoglobinuria. These attacks are especially likely to occur during prolonged exercise after fasting, eating a high-fat diet, or during cold weather. Occasionally after fasting alone, spontaneous muscle breakdown may occur. One patient studied in detail was excessively slow in producing ketones when he fasted. His mylagias and weakness appeared to be alleviated by beta-hydroxybutyrate. Of eight other patients thought to have idiopathic recurrent myoglobinuria, three were found to have myophosphorylase deficiency, whereas five did not have deficiency of either enzyme. Carnitine palmityl transferase deficiency may be more common than previously supposed, may be in part amenable to dietary therapy, can be easily distinguished from myophosphorylase deficiency, and may provide insight into the metabolism of fatty acids and ketone bodies as well as energy requirements of skeletal muscle.
There is now a great deal of evidence to link genetic defects of pyruvate metabolism to brain disease. Experimental evidence is reviewed in Chapter 12, and clinical evidence has been reviewed above. Severe lesions of components of the pyruvate dehydrogenase complex are associated with severe generalized brain disease, and milder defects with inherited ataxias. Nearly half of one series of our ataxic patients had deficient activity of pyruvate dehydrogenase, and 40% of another series have deficient activity of the lipoamide dehydrogenase component. This last group corresponds to 60% of the patients with Friedreich's ataxia and its clinical variants at UCLA. There is an association between defective activity of lipoamide dehydrogenase and disease, and the data suggest there is a structural mutation of the gene for the enzyme. Preliminary studies suggest that obligate heterozygotes as a group have enzyme activities between those for controls and those for patients. Moreover, the obligate heterozygotes from families in which there are kinetic defects of lipoamide dehydrogenase also appear to have kinetic abnormalities of the enzyme. The ataxic patients with reduced lipoamide dehydrogenase activity currently fall into two clinical groups. One is ragged-red ataxia, and the other is a disorder that is a subgroup of the classic Friedreich's ataxia syndrome. Studies need to be undertaken on a larger group of patients, with more diverse inherited ataxias, to test the present clinical associations of the enzyme defect. A dietary treatment derived from a knowledge of the presumed defect has modified the ataxia that is associated with defects of pyruvate decarboxylase, but the diet has not yet been tested with defects of lipoamide dehydrogenase.
Physostigmine improved videotape scores of ataxia in patients with various inherited ataxias. This improvement occurred in 12 out of 12 patients when the drug was given as a single dose and in nine of 11 patients when the drug and placebo were given in a long-term, double-blind randomized trial. Patients report various mild to moderate clinical benefits after the sustained use of physostigmine for 6 to 36 months. Videotape scores showed an average of 30% numerical improvement in seven patients after 6 months' sustained treatment. The acute responses are not blocked by methylscopolamine, methylscopolamine did not make ataxia more severe, nor have any patients had fasciculations or changes in strength while on physostigmine. We therefore presume that a central cholinergic mechanism plays some role in the pathophysiology of the inherited ataxias. We do not have direct data on the site or nature of this mechanism. Further studies with other cholinergic agents are now required to investigate the effects and potential clinical efficacy of this class of compounds more completely than has been done up to now.
Explore the source record for details and available documents.
Radiochemical methods are described in detail to measure the activities of the pyruvate dehydrogenase complex and of the ketoglutarate dehydrogenase complex in platelet-enriched fractions. Determinations can be completed in one day with as little as 5 ml of venous blood. Activities are proportional to the length of the incubation and the amount of tissue protein added, show appropriate dependence on added cofactors, are stable for up to 2 days at -20 degrees C, and do not appear to be affected by diet. The pyruvate dehydrogenase complex appears to be fully activated (dephosphorylated) in these preparations. Activities were comparable in platelet-enriched fractions from 25 normal subjects and 25 patients with a variety of neurological and psychiatric diagnoses. Mean values (+/- S.E.M.) for these 50 individuals were 169+/-9 pmol/min per mg protein for the pyruvate dehydrogenase complex and 535+/-27 pmol/min per mg protein for the ketoglutarate dehydrogenase complex. These values are comparable to those found in cultured skin fibroblast with similar techniques. Deficient pyruvate dehydrogenase activity (19+/-6 and 11+/-4 pmol/min per mg protein) was demonstrated in platelet-enriched preparations from two brothers whose fibroblasts had previously been shown to be deficient in pyruvate dehydrogenase and who responed to a ketogenic diet. Experimental detail critical to obtaining reproducible results with these methods are stressed (notably the crucial importance of maintaining the purity of the radioactive substrates). These techniques allow identification of patients with pyruvate dehydrogenase deficiencies within one day without requiring liver or muscle biopsy.
Physostigmine was given to 12 patients with various spincerebellar degenerations, and neurologic examinations were recorded on video tapes and assessed on a semiquantitative scale. Forty minutes after a single dose, the scores improved by 35.7 +/- 4.7 percent (means +/- SEM). Eight patients were then studied over sequential 3-month periods by a randomized double-blind trial of physostigmine versus placebo. With physostigmine, scores were 33.9 +/- 8.3 percent better than before treatment or with placebo. Further investigations of cholinergic drugs seem warranted in patients with these diseases.
Since patients with Friedreich's ataxia appear to oxidize pyruvate slowly, we measured the activity of the pyruvate dehydrogenase complex in disrupted fibroblasts from four patients with this syndrome and one patient with a clinical variant. The activity was 43 +/- 4 per cent of that in 16 controls (mean +/- S.E.M., P less than 0.001). The activity of the 2-oxoglutarate dehydrogenase complex was also lower in the patients' cells than in those of controls (50 +/- 2 per cent, P less than 0.001). However, the activity of cytochrome-c oxidase was normal (126 +/- 43 per cent of controls). Mixing experiments gave no evidence of soluble enzyme inhibitors or activators, and the addition of excess substrate or cofactor did not ameliorate the deficiencies. White blood cells from one of the patients had low activities of both complexes. Mutations of these dehydrogenase complexes occur in some patients with Friedreich's ataxia and lead to abnormally low activity of an enzyme of the tricarboxylic acid cycle.
Two brothers, aged 11 years 6 months and 2 years 3 months, with psychomotor and growth retardation, episodes of weakness, ataxia, ophthalmoplegia, and elevated levels of blood pyruvate were shown to have a deficiency in the pyruvate dehydrogenase complex (PDH). When they ate a diet high enough in fats to cause ketonemia but not acidosis, there was a fall in blood pyruvate levels, a decrease in the frequency and severity of the episodes of neurological deterioration, an increased rate of growth and development in the younger brother, and increased strength and endurance in the older one. The possibility of dietary treatment makes the early diagnosis of PDH deficiency more important. Determination of blood pyruvate and lactate levels following a standard glucose meal (glucose-pyruvate test) appears to be the most reliable screening test for this condition.
Whether pure thiamine deficiency produces a neuropathy in Mammalia is still debated. Rats were pair-fed-synthetic diets with and without thiamine. When studied histochemically, soleus muscles from thiamine-deficient rats showed (1) small, angular fibers that had high NADH dehydrogenase activities; (2) a loss of 43% of type II (FOG) fibers; (3) decreased intensity of the reaction for betaOHB dehydrogenase; and (4) fibers with subsarcolemmal collections resembling "ragged-red" muscle. Electron microscopy revealed degeneration of some small myelin sheaths of distal and intramuscular nerves; atrophic, degenerating, hypoosmophilic muscle fibers in soleus and vastus medialis; and scattered muscle fibers with abnormal collections of deranged mitochondria accompanied by lipid droplets. These abnormalities, not found in control muscles, indicate that both motor neuropathy and mild mitochondrial changes, such as are seen in the "ragged-red" diseases, are induced by pure thiamine deficiency.