Friedreich's ataxia 1980. An overview of the physiopathology

PathIN: an integrated tool for the visualization of pathway interaction networks

PathIN is a web-service that provides an easy and flexible way for rapidly creating pathway-based networks at several functional biological levels: genes, compounds and reactions. The tool is supported by a database repository of reference pathway networks across a large set of species, developed through the freely available information included in the KEGG, Reactome and Wiki Pathways database repositories. PathIN provides networks by means of five diverse methodologies: (a) direct connections between pathways of interest, (b) direct connections as well as the first neighbours of the given pathways, (c) direct connections, the first neighbours and the connections in between them, and (d) two additional methodologies for creating complementary pathway-to-pathway networks that involve additional (missing) pathways that interfere in-between pathways of interest. PathIN is expected to be used as a simple yet informative reference tool for understanding networks of molecular mechanisms related to specific diseases.

Mitochondrial pathophysiology in Friedreich's ataxia

Neurological examination indicates that Friedreich's ataxia corresponds to a mixed sensory and cerebellar ataxia, which affects the proprioceptive pathways. Neuropathology and pathophysiology of Friedreich's ataxia involves the peripheral sensory nerves, dorsal root ganglia, posterior columns, the spinocerebellar, and corticospinal tracts of the spinal cord, gracile and cuneate nuclei, dorsal nuclei of Clarke, and the dentate nucleus. Involvement of the myocardium and pancreatic islets of Langerhans indicates that it is also a systemic disease. The pathophysiology of the disease is the consequence of frataxin deficiency in the mitochondria and cells. Some of the biological consequences are currently recognized such as the effects on iron-sulfur cluster biogenesis or the oxidative status, but others deserve to be studied in depth. Among physiological aspects of mitochondria that have been associated with neurodegeneration and may be interesting to investigate in Friedreich's ataxia we can include mitochondrial dynamics and movement, communication with other organelles especially the endoplasmic reticulum, calcium homeostasis, apoptosis, and mitochondrial biogenesis and quality control. Changes in the mitochondrial physiology and transport in peripheral and central axons and mitochondrial metabolic functions such as bioenergetics and energy delivery in the synapses are also relevant functions to be considered. Thus, to understand the general pathophysiology of the disease and fundamental pathogenic mechanisms such as dying-back axonopathy, and determine molecular, cellular and tissue therapeutic targets, we need to discover the effect of frataxin depletion on mitochondrial properties and on specific cell susceptibility in the nervous system and other affected organs.

Friedreich ataxia: molecular mechanisms, redox considerations, and therapeutic opportunities

Mitochondrial dysfunction and oxidative damage are at the origin of numerous neurodegenerative diseases like Friedreich ataxia and Alzheimer and Parkinson diseases. Friedreich ataxia (FRDA) is the most common hereditary ataxia, with one individual affected in 50,000. This disease is characterized by progressive degeneration of the central and peripheral nervous systems, cardiomyopathy, and increased incidence of diabetes mellitus. FRDA is caused by a dynamic mutation, a GAA trinucleotide repeat expansion, in the first intron of the FXN gene. Fewer than 5% of the patients are heterozygous and carry point mutations in the other allele. The molecular consequences of the GAA triplet expansion is transcription silencing and reduced expression of the encoded mitochondrial protein, frataxin. The precise cellular role of frataxin is not known; however, it is clear now that several mitochondrial functions are not performed correctly in patient cells. The affected functions include respiration, iron-sulfur cluster assembly, iron homeostasis, and maintenance of the redox status. This review highlights the molecular mechanisms that underlie the disease phenotypes and the different hypothesis about the function of frataxin. In addition, we present an overview of the most recent therapeutic approaches for this severe disease that actually has no efficient treatment.

Beer and bread to brains and beyond: can yeast cells teach us about neurodegenerative disease?

For millennia, humans have harnessed the astonishing power of yeast, producing such culinary masterpieces as bread, beer and wine. Therefore, in this new millennium, is it very farfetched to ask if we can also use yeast to unlock some of the modern day mysteries of human disease? Remarkably, these seemingly simple cells possess most of the same basic cellular machinery as the neurons in the brain. We and others have been using the baker's yeast, Saccharomyces cerevisiae, as a model system to study the mechanisms of devastating neurodegenerative diseases such as Parkinson's, Huntington's, Alzheimer's and amyotrophic lateral sclerosis. While very different in their pathophysiology, they are collectively referred to as protein-misfolding disorders because of the presence of misfolded and aggregated forms of various proteins in the brains of affected individuals. Using yeast genetics and the latest high-throughput screening technologies, we have identified some of the potential causes underpinning these disorders and discovered conserved genes that have proven effective in preventing neuron loss in animal models. Thus, these genes represent new potential drug targets. In this review, I highlight recent work investigating mechanisms of cellular toxicity in a yeast Parkinson's disease model and discuss how similar approaches are being applied to additional neurodegenerative diseases.

Iron dysregulation in Friedreich ataxia

Friedreich ataxia is the most common hereditary ataxia. The signs and symptoms of the disorder derive from decreased expression of the protein frataxin, which is involved in iron metabolism. Frataxin chaperones iron for iron-sulfur cluster biogenesis and detoxifies iron in the mitochondrial matrix. Decreased expression of frataxin is associated with impairments of iron-sulfur cluster biogenesis and heme synthesis, as well as with mitochondrial dysfunction and oxidative stress. Compounds currently in clinical trials are directed toward improving mitochondrial function and lessening oxidative stress. Iron chelators and compounds that increase frataxin expression are under evaluation. Further elucidation of frataxin's function should lead to additional therapeutic approaches.

Movement disorders in Friedreich's ataxia

Since the discovery of the gene mutation causing Friedreich's ataxia (FA), the rich spectrum of clinical manifestations of this autosomal recessive disorder is being increasingly recognized. Movement disorders besides ataxia, however, have not been fully characterized in patients with FA. We describe here two young male patients who, in addition to progressive ataxia, kinetic tremor and other typical features of FA, also manifest axial and limb dystonia. The primary purpose of this report is to draw attention to the broad spectrum of hyperkinetic movement disorders that can present as or be associated with FA.

Effects of the novel cyclosporine derivative PSC833 on glucose metabolism in rat primary cultures of neuronal and glial cells

Cyclosporine A (CsA) and the cyclosporine degrees congener PSC833 are known to cause transient CNS symptoms at high dosages in animal and man. Since impaired glucose metabolism plays a fundamental role in many heriditary and drug-induced neurological disorders, it was the purpose of the present study to evaluate whether this mechanism of pathogenesis might apply to PSC833 and CsA, using neural cells from rats. PSC833 and CsA were investigated in primary cultures of rat neuronal and glial cells at the concentration of 0.1, 1, 10, and 20 microM for 24 and 48 hr. Lactate dehydrogenase was determined as a marker of cytotoxicity. Cell proliferation was determined in astrocytes. Cellular glucose metabolism was investigated by 13C-NMR using [1-13C]glucose as a substrate. Glucose and lactate concentrations in the cell culture supernatants were determined spectrophotometrically. PSC833 at 10 microM was not cytotoxic in neuronal or glial cells nor did it inhibit proliferation in astrocytes 24 hr after incubation. Under the same conditions, the determination of [1-13C]glucose and [3-13C]lactate revealed significantly increased glucose consumption and lactate production in both cell types, as well as decreased levels of Krebs cycle intermediates. In the cell culture medium of both cell types after treatment with 10 microM PSC833, the rates of glucose consumption and lactate formation increased in comparison to controls, between 60-83% and 54-78%, respectively. PSC833 (10 microM) and CsA (20 microM) resulted in nearly similar increased glucose consumption and lactate production. The major PSC833 metabolite in rats, M9, which was devoid of CNS effects, did not cause significant changes in glucose metabolism. The present data suggest that PSC833-impaired tricarboxylic acid cycle activity, resulting in decreased Krebs cycle metabolites, can cause energy depletion and acidosis, which might contribute to the transient neurological symptoms of PSC833 and CsA.

Metal ion transport in eukaryotic microorganisms: insights from Saccharomyces cerevisiae

Metal ions such as iron, copper, manganese, and zinc are essential nutrients for all eukaryotic microorganisms. Therefore, these organisms possess efficient uptake mechanisms to obtain these nutrients from their extracellular environment. Metal ions must also be transported into intracellular organelles where they function as catalytic and structural cofactors for compartmentalized enzymes. Thus, intracellular transport mechanisms are also present. When present in high levels, metal ions can also be toxic, so their uptake and intracellular transport is tightly regulated at both transcriptional and post-transcriptional levels to limit metal ion overaccumulation and facilitate storage and sequestration. Remarkable molecular insight into these processes has come from recent studies of the yeast Saccharomyces cerevisiae. This organism, which is the primary subject of this chapter, serves as a useful paradigm to understand metal ion metabolism in other eukaryotic microbes.

Echocardiographic features of genetic diseases: part 1. Cardiomyopathy

Introduction To The Series Genetic disorders have characteristic cardiovascular manifestations. These cardiovascular abnormalities often are a major determinant of the morbidity and mortality in this patient population. Some characteristics are unique and can be detected with echocardiography. Drs Alizad and Seward have compiled in this series a review of genetic disorders that have recognizable morphologic and/or functional cardiovascular abnormalities. The following topics will be explored, with examples from the database of the Mayo Clinic Echocardiography Laboratory:Cardiomyopathy Storage disease Shunts Connective tissue Tumors Complex cardiovascular defects Complex genetic disorders Organ system

The molecular biology of metal ion transport in Saccharomyces cerevisiae

Transition metals such as iron, copper, manganese, and zinc are essential nutrients. The yeast Saccharomyces cerevisiae is an ideal organism for deciphering the mechanism and regulation of metal ion transport. Recent studies of yeast have shown that accumulation of any single metal ion is mediated by two or more substrate-specific transport systems. High-affinity systems are active in metal-limited cells, whereas low-affinity systems play the predominant roles when the substrate is more abundant. Metal ion uptake systems of cells are tightly controlled, and both transcriptional and posttranscriptional regulatory mechanisms have been identified. Most importantly, studies of S. cerevisiae have identified a large number of genes that function in metal ion transport and have illuminated the existence of importance of gene families that play related roles in these processes in mammals.

Normal serum iron and ferritin concentrations in patients with Friedreich's ataxia

Friedreich's ataxia (FRDA) is caused by point mutations or trinucleotide repeat expansions in both alleles of the gene encoding frataxin. Studies of frataxin homologues in lower eukaryotes suggest that mitochondrial iron accumulation may underlie the pathophysiology of FRDA. To evaluate the possible role of iron-chelation therapy for FRDA, we measured serum iron and ferritin concentrations in 10 FRDA patients. The measurements were within normal limits, suggesting that iron-chelation therapy for FRDA may be problematic.

Respiratory deficiency due to loss of mitochondrial DNA in yeast lacking the frataxin homologue

Friedreich's ataxia (FRDA) is an autosomal recessive degenerative disorder that primarily affects the nervous system and heart. Patients with FRDA have point mutations or trinucleotide repeat expansions in both alleles of FRDA, which encodes a protein termed frataxin. We show that the yeast frataxin homologue, which we have named YFH1, localizes to mitochondria and is required to maintain mitochondrial DNA. The YFH1-homologous domain of frataxin functions in yeast and a disease-associated missense mutation of this domain, or the corresponding domain in YFH1, reduces function. Our data suggest that mitochondrial dysfunction contributes to FRDA pathophysiology.

Regulation of mitochondrial iron accumulation by Yfh1p, a putative homolog of frataxin

The gene responsible for Friedreich's ataxia, a disease characterized by neurodegeneration and cardiomyopathy, has recently been cloned and its product designated frataxin. A gene in Saccharomyces cerevisiae was characterized whose predicted protein product has high sequence similarity to the human frataxin protein. The yeast gene (yeast frataxin homolog, YFH1) encodes a mitochondrial protein involved in iron homeostasis and respiratory function. Human frataxin also was shown to be a mitochondrial protein. Characterizing the mechanism by which YFH1 regulates iron homeostasis in yeast may help to define the pathologic process leading to cell damage in Friedreich's ataxia.

Glucose intolerance in first-degree relatives of patients with Friedreich's ataxia is associated with insulin resistance: evidence for a closely linked inherited trait

Multiple and different genetic defects may be associated with the development of diabetes mellitus. Friedreich's ataxia (FA) is an autosomal recessively inherited neurologic disease associated with a high prevalence of diabetes. We previously demonstrated that patients with FA have insulin resistance prior to the development of overt diabetes mellitus. To determine if insulin resistance is an inherited characteristic in this group, we performed oral glucose tolerance tests (OGTT) on first-degree relatives, 21 parents and 17 siblings, of patients with FA. While fasting concentrations were normal, both glucose and insulin concentrations in response to oral glucose were significantly elevated compared with controls. Corrected insulin responses, CIR = I x 100/G (G-70) (I = insulin, G = glucose), were not different from controls, whereas peripheral insulin activities, A = 10(4)/Ip Gp (p = values of I and G at peak glucose concentration), were significantly decreased (FA, 0.66 +/- 0.11, P less than .001; parents, 0.63 +/- 0.06, P less than .001; siblings, 0.72 +/- 0.09, P less than .01; v controls, 1.52 +/- 0.19), indicating the presence of insulin resistance in patients and first-degree relatives. Multiple discriminant analysis was used to separate patients with FA from controls. The combination of GLUT (sum of glucose values 0 to 3 hours of the OGTT) and CIR achieved significant separation (P less than .0004). Subsequent assignment of the relatives showed that 17 of 18 parents and 11 of 16 siblings (69%) fell in the range of FA, rather than with controls. These data suggest that insulin resistance is an inherited trait in this group.(ABSTRACT TRUNCATED AT 250 WORDS)

Friedreich's ataxia: electrophysiologic and histologic findings in patients and relatives

Peripheral nerve conduction velocity and cortical evoked potentials were investigated in 48 patients with Friedreich's disease and in 35 relatives. There were 14 patients and 2 relatives who underwent sural nerve biopsy. In the patients sensory conduction velocity was moderately slowed, whereas sensory responses were markedly reduced. Nerve biopsy showed a severe loss of large myelinated fibers and no demyelination. On teased nerve fiber preparations, most fibers presented uniformly short internodes. No correlation was seen between sensory conduction findings or histologic abnormalities and clinical disability. In patients SSEP changes, which were constant, and VEPs, which were frequently involved, were unrelated to the severity or duration of clinical disability. There were 14 relatives who showed clinical signs of Friedreich's disease. Slightly decreased distal conduction velocity along sensory fibers was observed in more than half of the relatives. Nerve biopsy was noncontributory. In conclusion, we could not determine whether the abnormalities observed in the siblings were an expression of a heterozygotic condition, or whether they were early signs of the disease.

Coronary disease, cardioneuropathy, and conduction system abnormalities in the cardiomyopathy of Friedreich's ataxia

Abnormalities of the heart are a frequent and possibly ubiquitous problem in patients with Friedreich's ataxia, but their pathogenesis is unclear. Postmortem findings are reported from the hearts of three patients with Friedreich's ataxia who died of congestive heart failure and atrial arrhythmias. Particular attention was paid to the following: the large and small coronary arteries, the nerves and ganglia, the conduction system, and the histological and cellular features of the cardiomyopathy. There were pleomorphic nuclei and focal fibrosis and degeneration throughout each heart including the conduction system. There were distinctive abnormalities of both large and small coronary arteries, and focal degeneration of nerves and ganglia. These observations suggest a mosaic concept for the pathogenesis for the cardiomyopathy of Friedreich's ataxia that involves the interplay of molecular faults, cardiomyopathy, cardioneuropathy, and coronary disease.

Spectrum of cardiac involvement in Friedreich's ataxia: clinical, electrocardiographic and echocardiographic observations

Combined 2-dimensional and M-mode echocardiography was used to assess the cardiac status of 22 patients with Friedreich's ataxia, and the findings were correlated with the clinical and electrocardiographic (ECG) data. Mean age at onset of Friedreich's ataxia was 8 years (range 3 to 18); mean age at echocardiography was 18 years (range 8 to 39). Echocardiographic findings were abnormal in 19 patients (86%). The 3 patients with normal echocardiographic findings did not have cardiac symptoms, but 1 had ECG repolarization abnormalities. Concentric left ventricular (LV) thickening, the most common echocardiographic finding, was found in 15 patients (68%) and in all 15 the papillary muscles were thickened. These 15 patients had ECG repolarization abnormalities and 5 had left-axis deviation; however, only 3 satisfied ECG criteria for LV or right ventricular hypertrophy. Two of the 15 patients (9%) had symptoms of heart failure. Two patients had asymmetric septal thickening without clinical evidence of LV outflow tract obstruction; neither had cardiac symptoms, but both had ECG repolarization abnormalities. Two patients showed a dilated cardiomyopathy pattern; both had heart failure and atrial flutter. One of these patients died, and necropsy revealed 4-chamber cardiac dilatation, biventricular hypertrophy and histologic findings of diffuse interstitial fibrosis, myocellular hypertrophy and necrosis. This study revealed a wide spectrum of cardiac abnormalities in patients with Friedreich's ataxia.

Sensory and motor peripheral neuropathy in olivopontocerebellar atrophy

We report the findings of an electrophysiological study in 9 patients affected by olivopontocerebellar atrophy, 4 with a dominant form and 5 with a sporadic form. Superficial peroneal nerve biopsy was obtained from 2 patients. The electrophysiological alterations were signs of collateral reinnervation and loss of motor units, decrease in sensory potential amplitude and increase in distal motor latency. Only a slight reduction in motor and sensory conduction velocity was observed in some cases. Nerve biopsy showed slight reduction of the number of myelinated fibres. In the first case, fibre diameter distribution was unimodal, due to reduction of myelinated fibres of large diameter, in the second case there was no significant alteration of the fibre distribution. In both cases short internodes were present with no signs of segmental demyelination, remyelination or axonal degeneration. The alterations observed in the peripheral nervous system are probably secondary to a lesion of the posterior root ganglion and the anterior horn cell in the spinal cord.

The inherited ataxias

Clinical, biochemical, and genetic studies have brought clarity to many issues concerning the inherited ataxias. The classification, diagnosis, and therapy of hereditary ataxias are now better understood although many questions remain. Basic defects are identified in some disorders.

Friedreich's ataxia: clinical involvement and evoked potentials

In 15 patients definitely affected by Friedreich's ataxia, precocious SEP abnormalities were constantly recorded independent of the duration of symptoms and the severity of clinical involvement; VEPs were frequently involved, but neither VEP abnormalities, nor visual impairment could be correlated with the severity or duration of Friedreich's ataxia clinical involvement; BAEPs were, to different extents, abnormal. These were completely dissociated from hearing disorders and significantly correlated (P less than 0.001) with Friedreich's ataxia clinical disability. Our observation of increased latency of the VEP P100 component and the early disappearance of BAEP Wave V with persistence of Wave I is in contrast with the hypothesis that changes are related to primary axonal degeneration. For practical purposes SEPs could help in the early diagnosis of Friedreich's ataxia, and BAEPs could be used for the electrophysiological monitoring of its clinical progression.

Cardiac malic enzyme in Friedreich's disease

We measured the activity of cytosolic and of mitochondrial malic enzyme in the hearts from 4 patients with Friedreich's disease and from two non-ataxic control subjects. There was a wide variability in the results and the slight overall decreases in both enzyme activities were not considered to be statistically significant. From these and other results, we conclude that deficient mitochondrial malic enzyme activity is not a constant or primary feature of Friedreich's disease.

The cardiomyopathy in Friedreich's ataxia: isotopic ventriculography and myocardial imaging with thallium-201

Myocardial scanning after the intravenous administration of Thallium 201 was used to evaluate regional myocardial perfusion in 14 patients with Friedreich's ataxia. Isotopic ventriculography was also used to assess left ventricular contractility. Myocardial images in patients with Friedreich's ataxia were found to be precociously abnormal irrespective of the degree of neurological impairment or of the severity of myocardial hypertrophy.

Friedreich's ataxia: electrophysiological and histological findings

Electromyography was performed, and motor and sensory nerve conduction velocities were measured in 19 patients definitely affected by Friedreich's ataxia. Biopsy of the sural nerve was also performed in 9 patients. Most patients presented a moderate to severe loss of motor units, a significant increase in mean duration of motor unit potentials, and in the incidence of polyphasic potentials. Short-lasting spontaneous activity was rarely seen. Conduction velocity along the motor and sensory fibres of the median and tibial nerves was moderately slowed, while distal conduction time to muscle was significantly increased and the sensory orthodromically-evoked response markedly reduced. Intraoperative electrophysiological recordings obtained during biopsy of the sural nerve in 4 patients were consistent with the changes conventionally observed in the median, tibial and sural (6 patients) nerves. Quantitative histology revealed a reduced number of total myelinated fibres with a severe loss of large fibres, and a moderate loss of fibres of less than 7 microns in diameter. In teased nerve fibre preparations, the most evident abnormality consisted of fibres with uniformly short internodal length, while signs of remyelination were less prominent. Signs of active axonal degeneration were rarely observed in electron microscopy. Electrophysiological and histological findings were uniformly distributed, and the changes were neither related to the duration nor to the severity of the clinical condition.

Evoked potential abnormalities in the various inherited ataxias

Visual (VEP), brainstem auditory (BAEP), and somatosensory (SEP) evoked potential tests were performed in 45 patients representing ten types of inherited disorders in which ataxia was the most prominent symptom. Comparable VEP abnormalities were present among all types of patients. Normal BAEP tests were recorded in most patients except those with olivopontocerebellar atrophy. SEP results were often more severely abnormal in patients with Friedreich's ataxia. The observations emphasize the similarity in expression of different metabolic-degenerative disorders. When these tests are used clinically, certain features of evoked potentials (especially left-right symmetry) are typical of the inherited ataxias as a group. Few distinguishing features differentiate the individual disorders.

Pyruvate dehydrogenase activity in the liver, brain and adipose-tissue of lipid-deprived developing rats. Effect of minute amounts of polyunsaturated fatty acids

The present experiment was carried out using the following diets: FF, fat-free, and LP in same diet with 0.7% sunflower oil - given to the progeny of females kept on the FF diet since the mating. after 10 mM Mg2+ activation of the PDH phosphatase, and rate of [1-14C[ pyruvate decarboxylation into acetyl-CoA ester units was determined in the liver, brain and adipose-tissue of the pair-fed developing rats.

RESULTS

In the male progeny, pyruvate dehydrogenase (PDH) activity was higher (61%) in the LP group livers than in the FF group livers, at the end of the 13 week experiment. Such a difference was not observed in the two group brains up to the 91 days postweaning, but was even larger (94%) between adipose-tissues of the LP and FF groups. In the female progeny kept 12 weeks on the diets, PDH activity in the LP group tissues was also higher than in the FF group tissues: 63% in the liver, 43% in adipose-tissues, and less than 10% in the brain. Therefore, a minute amount of lipids high in linoleic acid appeared to increase PDH activity, and especially in the liver and adipose-tissues of animals kept on a strictly fat-free diet. This stimulation of the PDH activity seems closely related to the phospholipid rehabilitation in the tissues (decrease in the trienoic, tetraenoic acid ratio values).

Quantitative metabolic profiling of alpha-keto acids in Friedreich's ataxia

The plasma distribution of alpha-keto acids was measured in 26 subjects including 8 patients with Friedreich's ataxia, 8 with the recessive spastic ataxia of Charlevoix-Sageunay and 10 healthy volunteers. The groups were matched with regards to age, sex, weight and the study was conducted under standardized dietary intake. The result indicate significant differences in the alpha-keto acids distribution between the groups.

Leukocyte valine dehydrogenase activity in Friedreich's ataxia

We studied the activity of valine dehydrogenase (VDH) in leukocytes of 14 Friedreich's ataxia patients and of 14 normal control subjects. There was a significant 26% mean decrease in enzyme activity in the patients, a finding which could be responsible for the chronic accumulation of some alpha-keto acids with toxic metabolic consequences in that disease. However the deficiency was not present in all patients with the typical symptoms, nor was its magnitude sufficient to be considered the primary genetic defect in Friedreich's Ataxia.

Oral lecithin and linoleic acid in Friedreich's ataxia: III. Biochemical results

Lecithin and safflower oil brought about the same changes in serum LAD activity and kinetics in patients with Friedreich's Ataxia as in controls when results of this double-blind crossover study were analyzed according to group assignation. According to functional stages, pretrial LAD activity decreased with advancing severity while Km for lipoamide increased. Lecithin and safflower oil supplements corrected the elevated Km for lipoamide but produced a further reduction in LAD activity. These changes may have been due to the increased intake of linoleic acid, a precursor of lipoic acid, which is present in high percentage in both lecithin and safflower oil. Results of the biochemical study thus agreed with the clinical data gathered during the course of the one-year trial in suggesting that linoleic acid may well have been the active factor through which biochemical and clinical improvement was previously observed in patients with Friedreich's Ataxia supplemented with lecithin.

Friedreich's disease 1982: etiologic hypotheses a personal analysis

The author reviews the arguments for and against the four etiologic hypotheses in Friedreich's disease that have been proposed since 1974: the "pyruvate hypothesis", the "lipid-membrane hypothesis", the "energy-defect hypothesis" and finally the "taurine hypothesis". While none of these hypotheses are mutually exclusive, the author shows that all of these mechanisms play some role in the pathophysiology of the symptoms, but that only the "taurine hypothesis" appears to be compatible with all the known facts and the biochemical abnormalities reported. The author proposed that the taurine retention defect (possibly due to a block in the high affinity-low capacity transport of taurine - The TH System) is a primary event in Friedreich's disease. Whether it is the primary genetic event still has to be determined.

Reduced formation of hippuric acid after oral benzoic acid in Friedreich's ataxia

We have observed a markedly decreased formation of hippuric acid after benzoic acid load in patients with typical Friedreich's Ataxia compared to normal control subjects. Since there is evidence for normal or even enhanced tauro-conjugation in the bile of patients with this disease, with a decreased G/T ratio, it is unlikely that co-factor or enzyme concentrations are the cause of this defect. We postulate decreased availability of the enzyme for glycine conjugation either to bile acids in the usual situation or to benzoic acid in the artefactual test condition. This could be due to the enzyme's preference for an increased amount of taurine substrate in the liver. The relationship of this observation to the other biochemical changes observed in Friedreich's Ataxia must still be established.

Oral lecithin and linoleic acid in Friedreich's ataxia: II. Clinical results

Twenty-two patients with Friedreich's Ataxia and ten normal controls were followed for one year and assessed as to their clinical performance after two successive six-month periods of lecithin or safflower oil. Results demonstrated no significant difference in performance scores according to group assignation, neither in patients nor in controls. According to stages, two patients in stage I and to a lesser degree, one patient in stage IV showed better scores for muscle strength and some motor accuracy and coordination tests with lecithin. Controls as groups maintained positive scores in all tests. Patients as groups showed negative mean values in nine out of eleven tests. Again as groups, patients receiving safflower oil demonstrated a mean 8% less deterioration than patients receiving lecithin. This study demonstrates that objective clinical tests and the participation of normal controls are a must in a therapeutic trial implicating patients with a progressive disorder such as Friedreich's Ataxia. The possible role of linoleic acid as the active factor from which clinical improvement proceeded in some specific patients and with early functional stages of the disease, has to be considered and reevaluated in the near future.

Biochemical and clinical studies of Friedreich's ataxia

A series of biochemical tests aimed at elucidating the fundamental cause has been applied to 20 patients with Friedreich's ataxia. Special emphasis was placed upon pyruvate metabolism. The results demonstrate no precisely identifiable defect in the metabolism of pyruvate but indicate an abnormality in glucose uptake and metabolism.