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

Onset features and time to diagnosis in Friedreich's Ataxia

Background

In rare disorders diagnosis may be delayed due to limited awareness and unspecific presenting symptoms. Herein, we address the issue of diagnostic delay in Friedreich’s Ataxia (FRDA), a genetic disorder usually caused by homozygous GAA-repeat expansions.

Methods

Six hundred eleven genetically confirmed FRDA patients were recruited within a multicentric natural history study conducted by the EFACTS (European FRDA Consortium for Translational Studies, ClinicalTrials.gov-Identifier NCT02069509). Age at first symptoms as well as age at first suspicion of FRDA by a physician were collected retrospectively at the baseline visit.

Results

In 554 of cases (90.7%), disease presented with gait or coordination disturbances. In the others (n = 57, 9.3%), non-neurological features such as scoliosis or cardiomyopathy predated ataxia. Before the discovery of the causal mutation in 1996, median time to diagnosis was 4(IQR = 2–9) years and it improved significantly after the introduction of genetic testing (2(IQR = 1–5) years, p < 0.001). Still, after 1996, time to diagnosis was longer in patients with a) non-neurological presentation (mean 6.7, 95%CI [5.5,7.9] vs 4.5, [4.2,5] years in those with neurological presentation, p = 0.001) as well as in b) patients with late-onset (3(IQR = 1–7) vs 2(IQR = 1–5) years compared to typical onset < 25 years of age, p = 0.03).

Age at onset significantly correlated with the length of the shorter GAA repeat (GAA1) in case of neurological onset (r = − 0,6; p < 0,0001), but not in patients with non-neurological presentation (r = − 0,1; p = 0,4). Across 54 siblings’ pairs, differences in age at onset did not correlate with differences in GAA-repeat length (r = − 0,14, p = 0,3).

Conclusions

In the genetic era, presentation with non-neurological features or in the adulthood still leads to a significant diagnostic delay in FRDA. Well-known correlations between GAA1 repeat length and disease milestones are not valid in case of atypical presentations or positive family history.

Mitochondrial dysfunction in neurons in Friedreich's ataxia

Friedreich's ataxia is a multisystemic genetic disorder within the family of mitochondrial diseases that is characterized by reduced levels of the essential mitochondrial protein frataxin. Based on clinical evidence, the peripheral nervous system is affected early, neuronal dysfunction progresses towards the central nervous system, and other organs (such as heart and pancreas) are affected later. However, little attention has been given to the specific aspects of mitochondria function altered by frataxin depletion in the nervous system. For years, commonly accepted views on mitochondria dysfunction in Friedreich's ataxia stemmed from studies using non-neuronal systems and may not apply to neurons, which have their own bioenergetic needs and present a unique, extensive neurite network. Moreover, the basis of the selective neuronal vulnerability, which primarily affects large sensory neurons in the dorsal root ganglia, large principal neurons in the dentate nuclei of the cerebellum, and pyramidal neurons in the cerebral cortex, remains elusive. In order to identify potential misbeliefs in the field and highlight controversies, we reviewed current knowledge on frataxin expression in different tissues, discussed the molecular function of frataxin, and the consequences of its deficiency for mitochondria structural and functional properties, with a focus on the nervous system.

Electrodiagnosis in neuromuscular disease

Electromyography (EMG) is an important diagnostic tool for the assessment of individuals with various neuromuscular diseases. It should be an extension of a thorough history and physical examination. Some prototypical characteristics and findings of EMG and nerve conduction studies are discussed; however, a more thorough discussion can be found in the textbooks and resources sited in the article. With an increase in molecular genetic diagnostics, EMG continues to play an important role in the diagnosis and management of patients with neuromuscular diseases and also provides a cost-effective diagnostic workup before ordering a battery of costly genetic tests.

[Diagnosis of a Friedreich's ataxia: contribution of electrophysical explorations]

The monitoring of scoliosis treatment can lead to discover its cause.

CASE REPORT

A 16-year-old patient was allowed in Center of Functional Rehabilitation for intensive orthopaedic treatment of a severe scoliosis. Electrophysiological explorations carried out within the framework of the monitoring of this treatment detected an axonal neuropathy with sensitive prevalence, whose association with clinical signs made it possible to diagnose Friedreich's disease, then confirmed by molecular biology.

CONCLUSION

Electrophysiological examination is useful in a Rehabilitation Center within the framework of the monitoring of the treatment proposed, more especially as it can make it possible to direct a diagnosis.

Small fibers involvement in Friedreich's ataxia

Although the involvement of large myelinated sensory fibers in Friedreich's ataxia (FA) is well documented, an impairment of unmyelinated fibers has not been described. We demonstrate an involvement of cutaneous unmyelinated sensory and autonomic nerve fibers in FA patients. We performed a morphological and functional study of cutaneous nerve fibers in 14 FA patients and in a population of control subjects. We used immunohistochemical techniques and confocal microscopy applied to punch skin biopsies from thigh, distal leg, and fingertip, and compared the density of epidermal nerve fibers (ENFs) with the results of mechanical pain sensation and thermal and tactile thresholds performed on hand dorsum, thigh, distal leg, and foot dorsum. We observed in our patients a statistically significant loss of ENFs, a reduced innervation of sweat glands, arrector pilorum muscles and arterioles, and an impairment of thermal and tactile thresholds and mechanical pain detection.

Influence of GAA expansion size and disease duration on central nervous system impairment in Friedreich's ataxia: contribution to the understanding of the pathophysiology of the disease

OBJECTIVE

To verify if GAA expansion size could account for the severity of the central nervous system involvement in Friedreich's ataxia (FA).

METHODS

Retrospective study of 52 FA patients (mean age 26.9+/-12.1 years; mean disease duration 10.6+/-7.6 years) homozygous for GAA expansion. Median nerve somatosensory evoked potentials (SSEPs) were available in 36 FA patients, upper limb motor evoked potentials (MEPs) to transcranial magnetic stimulation in 32, brainstem auditory evoked potentials (BAEPs) in 24, and visual evoked potentials (VEPs) in 34. N20, P100, MEP amplitude, SSEP and MEP central conduction time (CCT and CMCT), P100 latency and I-III and I-V interpeak latency, and a BAEP abnormality score were correlated with disease duration and GAA expansion size on the shorter (GAA1) and larger (GAA2) allele in each pair.

RESULTS

The GAA1 size inversely correlated with the N20 amplitude (r = -0.49; P<0. 01). Disease duration directly correlated with CMCT (r = 0.57; P<0.01) and BAEP score (r = 0.61; P<0.01) and inversely with MEP (r = -0.40; P<0.05) and P100 amplitude (r = -0.39; P<0.05).

CONCLUSIONS

Our data suggest that central somatosensory pathway involvement in FA is mainly determined by GAA1 expansion size. Vice versa, degeneration of pyramidal tracts, auditory and visual pathways seems to be a continuing process during the life of FA patients.

Electrophysiology and nerve biopsy: comparative study in Friedreich's ataxia and Friedreich's ataxia phenotype with vitamin E deficiency

The authors report a comparative study of peripheral nerve conductions and nerve biopsy and somatosensory evoked potentials between 15 patients with Friedreich's ataxia and 15 patients with Friedreich's ataxia phenotype with selective vitamin E deficiency. The patients in the two groups are of similar age, age of onset, and clinical phenotype. Peripheral motor nerve action potential amplitude, and conduction velocities are within normal ranges in the two groups. In the Friedreich's ataxia group there is an early and severe peripheral sensory axonal neuronopathy, characterised by an important reduction of the amplitude of sensory action potential, and important loss of myelinated fibres with complete disappearance of large myelinated fibres without any regenerative process. In the Friedreich's ataxia phenotype with selective vitamin E deficiency group there is slight-to-moderate axonal sensory neuropathy with normal to moderate decrease of large myelinated fibre density and important regeneration in nerve biopsy. Somatosensory evoked potentials are markedly involved in the two groups asserting a severe involvement of somatosensory pathway in lumbar, thoracic and cervical spinal cord. These findings suggest that the pathological mechanism involved in the two diseases are different: central peripheral axonopathy in Friedreich's ataxia and central distal axonopathy in Friedreich's ataxia phenotype with selective vitamin E deficiency.

Correlation of peripheral nerve fiber loss and trinucleotide repeats in Machado-Joseph disease

BACKGROUND

Machado-Joseph disease (MJD) is a dominantly inherited cerebellar ataxia associated with spasticity, ophthalmoplegia and dystonia. There has been no report of electrophysiological or histological alterations of the peripheral nervous system in patients with MJD.

METHODS

Four patients with MJD were identified by polymerase chain reaction. The peripheral nerves of these patients were subjected to electrophysiological testing and histological study. Correlation analyses were made between various clinical parameters and the electrophysiological and histological changes.

RESULTS

Electrophysiological studies demonstrated a marked reduction of sensory action potential, acute denervation changes on needle EMG, as well as mild decrease in the compound motor action potential. Light microscopy of the sural nerves revealed clear loss of myelinated fibers, and morphometry studies showed a loss of large myelinated fibers. Moreover, the severity of these pathological changes was found to be related to the CAG repeat length in the MJD gene.

CONCLUSION

Our findings indicated that the peripheral nervous system was frequently affected in patients with MJD. These findings were similar to those seen in Friedreich's ataxia, suggesting a loss of sensory and motor fibers probably following a lesion of the dorsal root ganglion and the anterior horns in the spinal cord. Furthermore, the number of CAG repeats seems to have an inverse relationship to the extent of pathological changes of the peripheral nerves.

Autosomal dominant cerebellar ataxia type I: multimodal electrophysiological study and comparison between SCA1 and SCA2 patients

A multimodal electrophysiological study was performed on 41 patients from 24 families with autosomal dominant cerebellar ataxia type I (ADCA I). Upper- and lower-limb motor evoked potentials (MEPs) to transcranial magnetic stimulation, median and tibial nerve somatosensory evoked potentials (Mn and Tn-SSEPs), orthodromic sensory (SCV) and motor conduction (MCV) velocity along median and tibial nerve, brainstem auditory evoked potentials (BAEPs), and visual evoked potentials (VEPs) were examined. Molecular analysis showed 2 SCA1 families and 2 families linked to the SCA2 locus. A sural nerve biopsy was performed in 5 patients. Brainstem damage of the auditory pathway was observed in 79% of patients examined. VEP abnormalities possibly of central origin were found in 52% of patients. MEP and SSEP abnormalities were differently distributed along the pathways examined: the longer the pathway, the higher the occurrence and severity of impairment. Peripheral dying-back neuropathy (confirmed by nerve bioptic data) was a frequent finding (56%). A progressive degenerative process involving first the longest tracts of the central motor and central and peripheral branches of somatosensory pathways is hypothesized in ADCA I. MEP abnormalities were more frequent in SCA1, and the sensory-motor neuropathy was more severe in SCA2.

Clinical aspects of hereditary ataxias

The hereditary ataxias are a group of complex genetic disorders the understanding of which is undergoing a revolution because of advances in molecular genetics. Within the last few years, at least seven different gene loci have been found to be responsible for these syndromes, and the search is on for additional loci that undoubtedly exist. This review summarizes the clinical features of the various hereditary ataxias with known gene loci, as well as others that are now defined on a clinical basis. It also deals with some of the imaging and neuropharmacologic advances that have been made in this group of disorders.

Clinicopathological study of the peripheral nervous system in Machado-Joseph disease

Three cases of histologically-proven Machado-Joseph disease (MJD) (clinically, types II and III) are described with special reference to the peripheral nervous system. We systematically and quantitatively analyzed the myelinated fiber densities in various nerves of three MJD patients and compared the results with the patients' clinical features and the pathological findings for the central nervous system (CNS). The results obtained were (1) motor system: The number of intermediate gammamotoneuron fibers was decreased prominently in all three MJD patients. In the type III MJD cases, the number of large alpha-motoneuron fibers also were decreased. (2) Sensory system: it generally was less involved than the motor system at the root level; but the large fibers of the distal portion were vulnerable. (3) Oculomotor system: the number of large oculomotor fibers was decreased markedly in all three cases, but there was relative preservation of parasympathetic fibers. (4) Autonomic system: the preganglionic sympathetic fibers from the intermediate lateral nucleus generally were preserved. These results suggest that in MJD the vulnerability of the peripheral nerves reflects the degree of loss of their original neuronal cells and varies according to the clinical phenotype. The characteristic peripheral neuropathy of MJD may be the result of axonal degeneration due to perikaryal neuronal damage in the central nervous system.

Late onset Friedreich's disease: clinical features and mapping of mutation to the FRDA locus

Twenty two patients from 17 families with Friedreich's disease phenotype but with onset ranging from the ages of 21 to 36 are described. Comparison with "typical" Friedreich's disease with onset before 20 years of age showed only a lower occurrence of skeletal deformities. The peripheral and central neurophysiological findings, sural nerve biopsy, and the neuroradiological picture did not allow the differentiation between "late onset" and "typical" Friedreich's disease. Duration of disease from onset to becoming confined to a wheelchair was five years longer in late onset patients. Sixteen patients and 25 healthy members from eight families were typed with the chromosome 9 markers MLS1, MS, and GS4 tightly linked to the FRDA locus. All families showed positive lod scores with a combined value of 5.17 at a recombination fraction of theta = 0.00. It is concluded that "late onset" Friedreich's disease is milder than the "typical" form and that it maps to the same locus on chromosome 9.

Sensory conduction study in chronic sensory ataxic neuropathy

Sensory conduction was studied in six patients with chronic sensory ataxic neuropathy of an idiopathic type and associated with Sjögren's syndrome. Motor nerve conduction velocities were normal in most cases, but sensory nerve potentials could not be evoked in a routine peripheral nerve conduction study. Cortical and cervical somatosensory evoked potentials (SEPs) and evoked potentials from Erb's point were barely recorded by median nerve stimulation at the wrist. When the median nerve was stimulated at more proximal points, clear potentials were recorded from Erb's point, but cortical SEPs were still hardly elicited. Thus the sensory nerves are centrally and peripherally involved in this condition, and the involvement is more prominent in the distal portion in the peripheral nerve. These findings suggest that central-peripheral distal axonopathy is a process involved in this illness and that the dorsal root ganglia may be primarily involved, in accord with previous pathological studies.

Sensory neuropathy in infantile onset spinocerebellar ataxia (IOSCA)

Infantile onset spinocerebellar ataxia with sensory neuropathy is a new, inherited multisystem disorder discovered in 19 Finnish patients. In order to define the neuropathy of the disease, we measured sensory nerve action potentials and nerve conduction velocities in 18 patients, and recorded somatosensory evoked potentials (SEP) in 10 patients and performed a sural nerve biopsy in 13 patients. The fixed and teased nerve fascicles were examined by light and electron microscopy, and the whole transverse section of a nerve fascicle was photographed and enlarged for morphometric measurements. Our investigation revealed an early onset, rapidly progressive axonal neuropathy: the sensory action potentials were decreased after the age of 2 and a severe loss of mainly large myelinated fibers was found.

Evoked potentials in inherited ataxias: a multimodal electrophysiological study

A multimodal electrophysiological study, including median nerve somatosensory evoked potentials (SSEPs), motor cortical stimulation (CS) and brainstem evoked potentials (BAEPs), was performed on 34 patients with hereditary ataxias (HAs): 15 with Friedreich's disease (FD), 10 with early onset cerebellar ataxia (EOCA), and 9 with autosomal dominant cerebellar ataxia (ADCA). A higher incidence of abnormal central motor conduction was observed in FD than in EOCA patients, but was never observed in ADCA. A relationship between central motor conduction abnormalities and disease duration and clinical impairment was found only in FD patients. All FD patients showed severe impairment of the SSEPs that was not related to disease duration. In EOCA patients, less frequent and more variable SSEP abnormalities were observed. The lowest incidence of central SSEP abnormalities was observed in ADCA. The BAEP findings in all 3 groups of patients (but particularly those with EOCA) suggest prevalent brainstem damage.

Is early onset cerebellar ataxia with retained tendon reflexes identifiable by electrophysiologic and histologic profile? A comparison with Friedreich's ataxia

An electrophysiologic and histologic study was performed on 18 patients affected by early onset cerebellar ataxia with retained tendon reflexes (EOCA). Sensory and motor conduction velocity (SCV, MCV) was measured along peripheral nerves in all patients, somatosensory (SSEP) and brainstem auditory evoked potentials (BAEP) were recorded in 13; cortical stimulation (CS) in 12, and sural nerve biopsy in 4 patients were also performed. The results as a whole allow a division of EOCA patients into 2 groups: with (7 patients) and without (11 patients) peripheral neuropathy. Among EOCA patients with neuropathy a differential diagnosis with Friedreich's disease patients was not possible according to BAEPs and CS, while SSEPs could differentiate 2 out 5 patients in whom they were performed.

Brain-stem auditory evoked potentials and blink reflex in Friedreich's ataxia

The brain-stem involvement in Friedreich's ataxia (FA) was studied by using brain-stem auditory evoked potentials (BAEPs) and the blink reflex. Ten out of 18 patients had abnormal BAEPs, the main abnormality being complete absence of responses and disappearance of wave V. Combined degeneration of the peripheral and central acoustic pathways probably accounts for these findings. The blink reflex was abnormal in 50% of the cases. The outstanding abnormality was bilateral delay of late responses with normal early response, which could be correlated with the known pallor of the descending trigeminal tracts. In contrast with BAEP findings, blink reflex abnormalities did not correlate with either the age of patients or the severity and duration of the disease. These data suggest a difference in susceptibility to degeneration between the auditory system and neuronal system subserving the blink reflex. We conclude that systematic BAEP and blink reflex recording is useful in the electrophysiological evaluation of FA patients.

Intrafamilial phenotype variation in Friedreich's disease: possible exceptions to diagnostic criteria

Three families are described which include members with "typical" Friedreich's disease (FD) and others who are ataxic but do not satisfy all the diagnostic criteria for that disease. In family A two patients have an early-onset, rapidly progressive FD, while two others have a late-onset, more benign form. In families B and C one member has "typical" FD, and another has a similar ataxic syndrome, except for preservation of knee jerks. Laboratory evaluation is consistent with the diagnosis of FD in all cases. FD diagnosis appears justified in secondary cases with late onset or preserved tendon reflexes, provided that the index case fulfils all diagnostic criteria. Whether the diagnosis of FD is tenable in sporadic "atypical" cases remains to be seen. Echocardiographic and neurophysiological examination may be valuable in classifying such cases.

AAEM minimonograph #34: polyneuropathy: classification by nerve conduction studies and electromyography

Electrodiagnostic evaluation of patients with suspected polyneuropathy is useful for detecting and documenting peripheral abnormalities, identifying the predominant pathophysiology, and determining the prognosis for certain disorders. The electrodiagnostic classification of polyneuropathy is associated with morphologic correlates and is based upon determining involvement of sensory and motor fibers and distinguishing between predominantly axon loss and demyelinating lesions. Accurate electrodiagnostic classification leads to a more focused and expedient identification of the etiology of polyneuropathy in clinical situations.

Genetic data and natural history of Friedreich's disease: a study of 80 Italian patients

The clinical and genetic features of 80 patients with Friedreich's disease from 64 families are described. Diagnostic criteria were: no evidence of dominant inheritance, onset by the age of 20 years, progressive unremitting ataxia of limbs and gait, and absence of knee and ankle jerks. Furthermore, at least one of the following accessory signs was present: dysarthria, extensor plantar response and echocardiographic evidence of hypertrophic cardiomyopathy. Two peaks of onset age were evident at 6-9 and 12-15 years. Analysis of intra-family variation of onset age and absence of clustering of cardiomyopathy and diabetes did not suggest genetic heterogeneity. Peripheral nerve impairment was an early finding and showed slight further progression, whereas involvement of the cerebellar and corticospinal pathways appeared later and mainly accounted for the progressive worsening of the disease.

Clinical and genetic heterogeneity in early onset cerebellar ataxia with retained tendon reflexes

A clinical and genetic study was performed on 20 patients affected by early onset cerebellar ataxia with retained tendon reflexes (EOCA). Mean age at onset was 8.8 (SD 6.0) years. The frequency distribution of age of onset significantly differed from the normal distribution. Consanguinity rate was 16.7% and segregation ratio 0.164. As well as ataxia, which was a constant feature, there were signs of involvement of the cortico-spinal tracts and/or peripheral nerves in most patients. Results of neurophysiological studies were not homogeneous, nor were morphological findings of the sural nerve biopsy. The data suggest that EOCA may be genetically and clinically heterogeneous.

Electrophysiological and histological follow-up study in 15 Friedreich's ataxia patients

A clinical and electrophysiological follow-up was carried out for 3 to 7 years on 15 patients with Friedreich's ataxia (FA). Sural nerve biopsy was performed once in all patients, and a second time 6-7 years later in three of them. Clinical worsening and progression of disturbance were evaluated according to IAP and IACR scales. Sensory orthodromic conduction along median and tibial nerves was typical of FA and did not change between first and last examinations, nor were there morphological changes between the first and the second sural nerve biopsies. Peripheral nerve involvement is thought to be a result of defective development of the largest neurons and to remain stable from a very early stage of the disease; the clinical worsening may then be due to a progressive involvement of the pyramidal tracts and the cerebellar pathways.

The neurophysiological profile of vitamin B12 deficiency

Reports of the incidence and severity of physiological abnormalities of vitamin B12 deficiency sharply differ. To resolve these controversies we performed evoked response and nerve conduction studies in 10 males with vitamin B12 deficiency. The minimum criteria for this diagnosis were diminished position and vibration sensation and vitamin B12 levels less than 220 pg/ml. We found normal BAERs in 9/10 patients. The central interpeak latencies of the median and peroneal SERs were abnormal in 4/10 and 8/8 patients, respectively. The VERs were abnormal in 7/10 patients. We found absent or diminished amplitudes of sural sensory and peroneal motor action potentials in 8/10 patients. Abnormal peroneal F response chronodispersion was present in 7/10 patients. Nerve conduction velocities (NCV) were normal in 9/10 patients. EMG demonstrated abnormalities consistent with denervation in lower extremity muscles in 8/10 patients. These studies present a profile of vitamin B12 deficiency: essentially normal BAERs, mildly abnormal VERs and median SERs, and markedly abnormal peroneal SERs. NCV studies are consistent with sensory-motor axonopathy.

Utility of short-latency evoked potentials in the classification of progressive, early onset cerebellar ataxias

In recent years, several authors have proposed new classifications of inherited ataxias, some of them being based on systematic clinical studies of large groups of patients. This methodic approach has led to the identification of new types of ataxias and helped the development of molecular biology research in these diseases. Up to now, nerve conduction velocity and evoked potential studies have not been considered in the classification of hereditary ataxias. We have studied the results of short latency evoked potentials in 102 patients affected by a early onset, progressive cerebellar ataxia. Based on the results of this study and a review of the literature on this subject, we will evaluate the utility of nerve conduction velocity and evoked potential recordings in the classification of this group of diseases.

Late onset recessive ataxia with Friedreich's disease phenotype

The Quebec Cooperative Study on Friedreich's ataxia required an onset before age 20 as an obligatory criterion of Friedreich's disease (FD). Harding included patients with onset before 25 years. We studied nine patients with FD phenotype but with onset ranging from 21 to 29 years (mean 24.4). Statistical analysis of the distribution and intrafamilial variation of onset age suggests that late onset Friedreich's disease (LOFD) is a distinct genetic entity or results from modifying genes in some families. Scoliosis was less common in LOFD than FD patients but otherwise the clinical picture was similar.

Central motor conduction in degenerative ataxic disorders: a magnetic stimulation study

Central motor conduction to small hand muscles was measured using magnetic stimulation of the motor cortex and electrical stimulation of proximal motor roots in 11 patients with Friedreich's ataxia, 10 patients with early onset cerebellar ataxia with retained tendon reflexes (EOCA) and 13 patients with late onset degenerative cerebellar disease (LOCD). Central motor conduction was abnormal in 91% with Friedreich's ataxia, 70% with EOCA and 38% with LOCD. Central motor conduction abnormalities were not specific to individual disorders but were more severe and were related to disease duration in Friedreich's ataxia and EOCA.