The number and sizes of reconstructed peripheral autonomic, sensory and motor neurons in a case or dysautonomia

Hereditary Sensory and Autonomic Neuropathies: Adding More to the Classification

PURPOSE OF REVIEW

Hereditary sensory and autonomic neuropathies (HSANs) are a clinically heterogeneous group of inherited neuropathies featuring prominent sensory and autonomic involvement. Classification of HSAN is based on mode of inheritance, genetic mutation, and phenotype. In this review, we discuss the recent additions to this classification and the important updates on management with a special focus on the recently investigated disease-modifying agents.

RECENT FINDINGS

In this past decade, three more HSAN types were added to the classification creating even more diversity in the genotype-phenotype. Clinical trials are underway for disease-modifying and symptomatic therapeutics, targeting mainly HSAN type III. Obtaining genetic testing leads to accurate diagnosis and guides focused management in the setting of such a diverse and continuously growing phenotype. It also increases the wealth of knowledge on HSAN pathophysiologies which paves the way toward development of targeted genetic treatments in the era of precision medicine.

The familial dysautonomia disease gene IKBKAP is required in the developing and adult mouse central nervous system

Hereditary sensory and autonomic neuropathies (HSANs) are a genetically and clinically diverse group of disorders defined by peripheral nervous system (PNS) dysfunction. HSAN type III, known as familial dysautonomia (FD), results from a single base mutation in the gene IKBKAP that encodes a scaffolding unit (ELP1) for a multi-subunit complex known as Elongator. Since mutations in other Elongator subunits (ELP2 to ELP4) are associated with central nervous system (CNS) disorders, the goal of this study was to investigate a potential requirement for Ikbkap in the CNS of mice. The sensory and autonomic pathophysiology of FD is fatal, with the majority of patients dying by age 40. While signs and pathology of FD have been noted in the CNS, the clinical and research focus has been on the sensory and autonomic dysfunction, and no genetic model studies have investigated the requirement for Ikbkap in the CNS. Here, we report, using a novel mouse line in which Ikbkap is deleted solely in the nervous system, that not only is Ikbkap widely expressed in the embryonic and adult CNS, but its deletion perturbs both the development of cortical neurons and their survival in adulthood. Primary cilia in embryonic cortical apical progenitors and motile cilia in adult ependymal cells are reduced in number and disorganized. Furthermore, we report that, in the adult CNS, both autonomic and non-autonomic neuronal populations require Ikbkap for survival, including spinal motor and cortical neurons. In addition, the mice developed kyphoscoliosis, an FD hallmark, indicating its neuropathic etiology. Ultimately, these perturbations manifest in a developmental and progressive neurodegenerative condition that includes impairments in learning and memory. Collectively, these data reveal an essential function for Ikbkap that extends beyond the peripheral nervous system to CNS development and function. With the identification of discrete CNS cell types and structures that depend on Ikbkap, novel strategies to thwart the progressive demise of CNS neurons in FD can be developed.

Summary:Ikbkap is essential for normal CNS development, neuronal survival and behavior, adding to our understanding of the role of the Elongator complex in the mammalian CNS.

Familial dysautonomia: History, genotype, phenotype and translational research

Familial dysautonomia (FD) is a rare neurological disorder caused by a splice mutation in the IKBKAP gene. The mutation arose in the 1500s within the small Jewish founder population in Eastern Europe and became prevalent during the period of rapid population expansion within the Pale of Settlement. The carrier rate is 1:32 in Jews descending from this region. The mutation results in a tissue-specific deficiency in IKAP, a protein involved in the development and survival of neurons. Patients homozygous for the mutations are born with multiple lesions affecting mostly sensory (afferent) fibers, which leads to widespread organ dysfunction and increased mortality. Neurodegenerative features of the disease include progressive optic atrophy and worsening gait ataxia. Here we review the progress made in the last decade to better understand the genotype and phenotype. We also discuss the challenges of conducting controlled clinical trials in this rare medically fragile population. Meanwhile, the search for better treatments as well as a neuroprotective agent is ongoing.

Brainstem reflexes in patients with familial dysautonomia

OBJECTIVE

Several distinctive clinical features of patients with familial dysautonomia (FD) including dysarthria and dysphagia suggest a developmental defect in brainstem reflexes. Our aim was to characterize the neurophysiological profile of brainstem reflexes in these patients.

METHODS

We studied the function of sensory and motor trigeminal tracts in 28 patients with FD. All were homozygous for the common mutation in the IKAP gene. Each underwent a battery of electrophysiological tests including; blink reflexes, jaw jerk reflex, masseter silent periods and direct stimulation of the facial nerve. Responses were compared with 25 age-matched healthy controls.

RESULTS

All patients had significantly prolonged latencies and decreased amplitudes of all examined brainstem reflexes. Similar abnormalities were seen in the early and late components. In contrast, direct stimulation of the facial nerve revealed relative preservation of motor responses.

CONCLUSIONS

The brainstem reflex abnormalities in FD are best explained by impairment of the afferent and central pathways. A reduction in the number and/or excitability of trigeminal sensory axons is likely the main problem.

SIGNIFICANCE

These findings add further evidence to the concept that congenital mutations of the elongator-1 protein (or IKAP) affect the development of afferent neurons including those carrying information for the brainstem reflex pathways.

Disturbances in affective touch in hereditary sensory & autonomic neuropathy type III

Hereditary sensory and autonomic neuropathy type III (HSAN III, Riley–Day syndrome, Familial Dysautomia) is characterised by elevated thermal thresholds and an indifference to pain. Using microelectrode recordings we recently showed that these patients possess no functional stretch-sensitive mechanoreceptors in their muscles (muscle spindles), a feature that may explain their lack of stretch reflexes and ataxic gait, yet patients have apparently normal low-threshold cutaneous mechanoreceptors. The density of C-fibres in the skin is markedly reduced in patients with HSAN III, but it is not known whether the C-tactile afferents, a distinct type of low-threshold C fibre present in hairy skin that is sensitive to gentle stroking and has been implicated in the coding of pleasant touch are specifically affected in HSAN III patients. We addressed the relationship between C-tactile afferent function and pleasant touch perception in 15 patients with HSAN III and 15 age-matched control subjects. A soft make-up brush was used to apply stroking stimuli to the forearm and lateral aspect of the leg at five velocities: 0.3, 1, 3, 10 and 30 cm/s. As demonstrated previously, the control subjects rated the slowest and highest velocities as less pleasant than those applied at 1–10 cm/s, which fits with the optimal velocities for exciting C-tactile afferents. Conversely, for the patients, ratings of pleasantness did not fit the profile for C-tactile afferents. Patients either rated the higher velocities as more pleasant than the slow velocities, with the slowest velocities being rated unpleasant, or rated all velocities equally pleasant. We interpret this to reflect absent or reduced C-tactile afferent density in the skin of patients with HSAN III, who are likely using tactile cues (i.e. myelinated afferents) to rate pleasantness of stroking or are attributing pleasantness to this type of stimulus irrespective of velocity.

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C-tactile afferents in hairy skin are believed to mediate affective touch.

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They are sensitive to slow brushing stimuli, which are perceived as pleasant.

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It is not known whether C-tactile afferents are affected in HSAN III.

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Ratings of pleasantness were reduced in 15 HSAN III patients compared to controls.

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We suggest that the density of C-tactile afferents is reduced in HSAN III.

Familial dysautonomia (Riley-Day syndrome): when baroreceptor feedback fails

Familial dysautonomia (FD) is a rare hereditary disorder caused by mutations within the gene that encodes for I-κ-B kinase complex associated protein (IKAP). A deficiency of IKAP affects the development of primary sensory neurons including those carrying baroreflex afferent volleys, a feature that explains their characteristic sensory loss and labile blood pressure. This review describes the history, the genotype of FD and the unusual cardiovascular autonomic phenotype of these patients. We outline the main consequences of a failure to receive information from arterial baroreceptors, including the characteristic "autonomic storms" and severe end-organ target damage.

Cardiac-locked bursts of muscle sympathetic nerve activity are absent in familial dysautonomia

Familial dysautonomia (Riley-Day syndrome) is an hereditary sensory and autonomic neuropathy (HSAN type III), expressed at birth, that is associated with reduced pain and temperature sensibilities and absent baroreflexes, causing orthostatic hypotension as well as labile blood pressure that increases markedly during emotional excitement. Given the apparent absence of functional baroreceptor afferents, we tested the hypothesis that the normal cardiac-locked bursts of muscle sympathetic nerve activity (MSNA) are absent in patients with familial dysautonomia. Tungsten microelectrodes were inserted percutaneously into muscle or cutaneous fascicles of the common peroneal nerve in 12 patients with familial dysautonomia. Spontaneous bursts of MSNA were absent in all patients, but in five patients we found evidence of tonically firing sympathetic neurones, with no cardiac rhythmicity, that increased their spontaneous discharge during emotional arousal but not during a manoeuvre that unloads the baroreceptors. Conversely, skin sympathetic nerve activity (SSNA), recorded in four patients, appeared normal. We conclude that the loss of phasic bursts of MSNA and the loss of baroreflex modulation of muscle vasoconstrictor drive contributes to the poor control of blood pressure in familial dysautonomia, and that the increase in tonic firing of muscle vasoconstrictor neurones contributes to the increase in blood pressure during emotional excitement.

Can loss of muscle spindle afferents explain the ataxic gait in Riley-Day syndrome?

The Riley-Day syndrome is the most common of the hereditary sensory and autonomic neuropathies (Type III). Among the well-recognized clinical features are reduced pain and temperature sensation, absent deep tendon reflexes and a progressively ataxic gait. To explain the latter we tested the hypothesis that muscle spindles, or their afferents, are absent in hereditary sensory and autonomic neuropathy III by attempting to record from muscle spindle afferents from a nerve supplying the leg in 10 patients. For comparison we also recorded muscle spindles from 15 healthy subjects and from two patients with hereditary sensory and autonomic neuropathy IV, who have profound sensory disturbances but no ataxia. Tungsten microelectrodes were inserted percutaneously into fascicles of the common peroneal nerve at the fibular head. Intraneural stimulation within muscle fascicles evoked twitches at normal stimulus currents (10-30 µA), and deep pain (which often referred) at high intensities (1 mA). Microneurographic recordings from muscle fascicles revealed a complete absence of spontaneously active muscle spindles in patients with hereditary sensory and autonomic neuropathy III; moreover, responses to passive muscle stretch could not be observed. Conversely, muscle spindles appeared normal in patients with hereditary sensory and autonomic neuropathy IV, with mean firing rates of spontaneously active endings being similar to those recorded from healthy controls. Intraneural stimulation within cutaneous fascicles evoked paraesthesiae in the fascicular innervation territory at normal stimulus intensities, but cutaneous pain was never reported during high-intensity stimulation in any of the patients. Microneurographic recordings from cutaneous fascicles revealed the presence of normal large-diameter cutaneous mechanoreceptors in hereditary sensory and autonomic neuropathy III. Our results suggest that the complete absence of functional muscle spindles in these patients explains their loss of deep tendon reflexes. Moreover, we suggest that their ataxic gait is sensory in origin, due to the loss of functional muscle spindles and hence a compromised sensorimotor control of locomotion.

Afferent baroreflex failure in familial dysautonomia

BACKGROUND

Familial dysautonomia (FD) is due to a genetic deficiency of the protein IKAP, which affects development of peripheral neurons. Patients with FD display complex abnormalities of the baroreflex of unknown cause.

METHODS

To test the hypothesis that the autonomic phenotype of FD is due to selective impairment of afferent baroreceptor input, we examined the autonomic and neuroendocrine responses triggered by stimuli that either engage (postural changes) or bypass (cognitive/emotional) afferent baroreflex pathways in 50 patients with FD and compared them to those of normal subjects and to those of patients with pure autonomic failure (PAF), a disorder with selective impairment of efferent autonomic neurons.

RESULTS

During upright tilt, in patients with FD and in patients with PAF blood pressure fell markedly but the heart rate increased in PAF and decreased in FD. Plasma norepinephrine levels failed to increase in both groups. Vasopressin levels increased appropriately in patients with PAF but failed to increase in patients with FD. Head-down tilt increased blood pressure in both groups but increased heart rate only in patients with FD. Mental stress evoked a marked increase in blood pressure and heart rate in patients with FD but little change in those with PAF.

CONCLUSION

The failure to modulate sympathetic activity and to release vasopressin by baroreflex-mediated stimuli together with marked sympathetic activation during cognitive tasks indicate selective failure of baroreceptor afference. These findings indicate that IKAP is critical for the development of afferent baroreflex pathways and has therapeutic implications in the management of these patients.

The R3 component of the electrically elicited blink reflex is present in patients with congenital insensitivity to pain

To clarify whether the R3 component of the electrically elicited blink reflex is a nociceptive response we studied two patients with congenital insensitivity to pain due to the impaired development of Adelta and C nerve fibers (hereditary sensory and autonomic neuropathy types III and IV). We postulated that if the R3 component is a nociceptive reflex, it should be absent in these patients. The R3 responses were elicited in both sides in both the patients at all intensities, strongly suggesting that the R3 component of the blink reflex is not a nociceptive response.

A world without pain or tears

The world of the child with familial dysautonomia (FD), a genetic disorder affecting development of the sensory and autonomic nervous system, is not idyllic. However, over the last 35 years advances in supportive treatments have improved morbidity and mortality. Recent genetic breakthroughs have further expanded thinking about this disorder and suggested innovative approaches to modifying genetic expression. This article reviews the current supportive treatment modalities and their rationale, as well as the suggested new treatments that may alter the function and prognosis of an individual affected with FD.

Familial dysautonomia

Familial dysautonomia (FD) is a neurodevelopmental genetic disorder within the larger classification of hereditary sensory and autonomic neuropathies, each caused by a different genetic error. The FD gene has been identified as IKBKAP. Mutations result in tissue-specific expression of mutant IkappaB kinase-associated protein (IKAP). The genetic error probably affects development, as well as maintenance, of neurons because there is neuropathological and clinical progression. Pathological alterations consist of decreased unmyelinated and small-fiber neurons. Clinical features reflect widespread involvement of sensory and autonomic neurons. Sensory loss includes impaired pain and temperature appreciation. Autonomic features include dysphagia, vomiting crises, blood pressure lability, and sudomotor dysfunction. Central dysfunction includes emotional lability and ataxia. With supportive treatment, prognosis has improved greatly. About 40% of patients are over age 20 years. The cause of death is usually pulmonary failure, unexplained sudden deaths, or renal failure. With the discovery of the genetic defect, definitive treatments are anticipated.

Primary sensory neurons in X-linked recessive bulbospinal neuropathy: histopathology and androgen receptor gene expression

Pathology of the primary sensory neurons was examined in 7 autopsied patients and 6 biopsied sural nerves from the patients with X-linked recessive bulbospinal neuronopathy (SBMA). Large myelinated fibers in the central rami (L-4 posterior root, L-4, T-7, and C-6 segment of the fasciculus gracilis), and in the peripheral rami (sural nerve) were diminished in a distally accentuated manner, while small myelinated and unmyelinate fibers were well preserved in number. Demylinating process and axonal atrophy was ubiquitous. The diameter frequency histograms of the dorsal root ganglion (DRG) neurons showed a decrease in the number of large diameter neurons and an increase in the number of small diameter neurons without substantial loss of whole number of neurons, which suggested that neuronal size was atrophied. These data suggested central and peripheral distal axonopathy with neuronal atrophy was the process of sensory neuron involvement. Expression of mutant androgen receptor mRNA with elongated CAG repeat in the DRG and sural nerve supported the view that sensory nerve involvement is the primary process in SBMA.

Hereditary sensory neuropathies

Hereditary sensory neuropathies have not shared in the major advances that have taken place in the molecular genetics of the hereditary demyelinating motor and sensory neuropathies. Thus far, classification depends upon their mode of inheritance and clinical features. The delineation of the various clinical syndromes is still not complete. This is a necessary preliminary to establishing the genetic basis of these neuropathies. The hereditary sensory neuropathies can be accordingly grouped into those with predominantly sensory and some associated autonomic features and those in which a sensory neuropathy is part of a spinocerebellar degeneration or other multisystem degeneration.

Somatic motor efferents in multiple system atrophy with autonomic failure: a clinico-pathological study

The myelinated fibers in the corticospinal tracts, ventral spinal roots, and the neurons in the ventral spinal horns were quantitatively examined in 8 autopsied cases of multiple system atrophy associated with autonomic failure. In these structures consisting of the somatic motor efferents, the main pathological feature was the size dependent-involvement of predominantly small-sized fibers and neurons. The small myelinated fibers were significantly depopulated, while the large myelinated fibers were well populated in the corticospinal tract. Neurons in the ventral horns were also involved, but those with a small diameter and located in the intermediate zone (Rexed's lamina VII, VIII) were markedly diminished. In the ventral spinal roots, in the fourth lumbar segments containing essentially no autonomic efferents, small myelinated fibers were also preferentially involved. These pathological changes in the small-sized fiber and neuron loss were examined in relation to the somatic and autonomic motor symptoms, particularly of pyramidal signs.

Invited review: autonomic dysfunction in peripheral nerve disease

The autonomic nervous system is affected in most peripheral neuropathies, but only in a small number of conditions, such as diabetes, amyloidosis, Guillain-Barré syndrome, porphyria, and familiar dysautonomia, is autonomic dysfunction of clinical importance. The pathological changes in the peripheral autonomic nervous system are similar to those in the peripheral somatic nerves. Autonomic disturbances are most likely to occur when there is acute demyelination or damage to small myelinated and unmyelinated fibers. Autonomic investigations should include tests of both sympathetic and parasympathetic function. Treatment consists of management of the underlying cause of peripheral neuropathy, physical and pharmacological measures.

Calcineurin and synaptophysin in the human spinal cord of normal individuals and patients with familial dysautonomia

This report concerns the immunohistochemical demonstration of two neuronal Ca2(+)-binding proteins, calcineurin and synaptophysin, in the spinal cord of normal controls and from patients with familial dysautonomia. In controls, calcineurin immunoreactivity was highly concentrated in small nerve cells and fibers of the substantia gelatinosa. Synaptophysin immunoreactivity was normally distributed throughout the spinal cord gray matter, being highly concentrated in the substantia gelatinosa, the dorsal nucleus of Clarke and the anterior horn. In patients with familial dysautonomia, no apparent changes in calcineurin immunoreactivity were found in the substantia gelatinosa. By contrast, there was a significant depletion of synaptophysin-positive axon terminals in the substantia gelatinosa and in the dorsal nucleus of Clarke of patients with familial dysautonomia.

Optic nerve dysfunction in familial dysautonomia

We examined 12 patients with familial dysautonomia who had clear corneas to determine if there was any optic nerve involvement. The patients ranged in age from 6 to 34 years. Visual acuity ranged from 20/20 to 20/100. Nineteen eyes of 12 patients (79%) had abnormal (mean +/- 3 S.D.) pattern reversal visual-evoked potentials as compared to 50 control eyes (P100 = 98.8 msec; S.D., +/- 4.5 msec). P100 latency appeared to worsen with age. Exodeviation was present in seven patients (58%) and correlated with visual acuity and P100 latency. Ophthalmoscopic examination showed some degree of optic nerve pallor in all eyes.

Disorders of the autonomic nervous system: Part 1. Pathophysiology and clinical features

Autonomic dysfunction may result from diseases that affect primarily either the central nervous system or the peripheral autonomic nervous system. The most common pathogenesis of disturbed autonomic function in central nervous system diseases is degeneration of the intermediolateral cell columns (progressive autonomic failure) or disease or damage to descending pathways that synapse on the intermediolateral column cells (spinal cord lesions, cerebrovascular disease, brainstem tumors, multiple sclerosis). The peripheral autonomic nervous system may be damaged in isolation in the acute and subacute autonomic neuropathies or in association with a generalized peripheral neuropathy. The peripheral neuropathies most likely to cause severe autonomic disturbance are those in which small myelinated and unmyelinated fibers are damaged in the baroreflex afferents, the vagal efferents to the heart, and the sympathetic efferent pathways to the mesenteric vascular bed. Acute demyelination of the sympathetic and parasympathetic nerves in the Guillain-Barré syndrome may also cause acute autonomic dysfunction. Although autonomic disturbances may occur in other types of peripheral neuropathy, they are rarely clinically important.

Preferential loss of large lumbar primary sensory neurons in carcinomatous sensory neuropathy

Morphometric studies at autopsy of a patient with sensory neuropathy associated with small-cell lung carcinoma showed preferential loss of large-diameter sensory nerve cell bodies (fifth lumbar dorsal root ganglion), marked decrease of large myelinated fibers in the dorsal root and sural nerve, and almost total loss of myelinated fibers in the fasciculus gracilis.

The spatial distribution of fiber loss in diabetic polyneuropathy suggests ischemia

Characterization and quantitation of the spatial distribution of pathological abnormalities along the length of nerves may be helpful in understanding the underlying mechanisms of diabetic polyneuropathy. To this end, by examining transverse sections of nerve roots and proximal-to-distal levels of lower limb nerves in 9 controls and 15 diabetic patients with polyneuropathy, we have determined the myelinated fiber (MF) number, size distribution, median diameter, and variability of density (MFs/mm2) among frames and among fascicles. Even in cases with mild polyneuropathy, fiber loss, a decrease in the median diameter, and an increase in the variability of density among frames and among fascicles began in proximal nerve and extended to distal levels. Multifocal fiber loss along the length of nerves and sprouting provide the best explanation for these findings. The pattern is dissimilar from that observed in diffuse metabolic disease of Schwann cells, neuronal degeneration, and dying-back neuropathy, but like that found in experimental ischemic neuropathy induced by embolization of nerve capillaries.

Familial dysautonomia in a non-Jewish girl, with histological evidence of progression in the sural nerve

A case of typical familial dysautonomia (HSN, type III) in a non-Jewish girl is reported. The number of unmyelinated fibres was found to be reduced and sural nerve biopsy showed evidence of past axonal degeneration. There was also marked endoneurial fibrosis and a lack of the largest myelinated fibres. Signs of histological progression not yet described in the sural nerve and other clinical and morphological features could be explained by different penetrance degrees of the disease.

Reduced neuronotrophic activity of fibroblasts from individuals with dysautonomia in cultures of newborn mouse sensory ganglion cells

The neuronotrophic activity of human skin fibroblast cell lines from two normal individuals and 3 individuals with Familial Dysautonomia (FD) was compared in terms of their ability to support neuron survival and neurite regeneration in cultures of newborn mouse sensory neurons. Neuronotrophic activity was assayed by culturing dissociated sensory neurons from newborn mice: (1) on fibroblast 'cell beds' consisting of monolayer cultures of living fibroblasts, (2) with medium that had been conditioned by monolayer fibroblast cultures and (3) with extracts of the cultured fibroblasts. Neurite regeneration was compared by determining the percentage of neurons that had regenerated neurites after 24 or 48 h in culture. Neuron survival was determined by counts at 48 h, 7 days and 14 days after culture initiation. Neurite regeneration and neuron survival was found to be significantly less on FD cell beds or with FD-conditioned medium than in replicate cultures with normal fibroblasts or their conditioned medium. The reduced neuronotrophic activity of FD fibroblasts or conditioned medium was still observed in the presence of antibody sufficient to block the neuronotrophic effects of purified nerve growth factor (NGF). Thus, fibroblasts from individuals with FD exhibit reduced neuronotrophic activity for newborn mouse sensory neurons that appears to be due to factor(s) other than NGF.

The measurement of motor cell volumes in rats

The volumes of cell bodies and nuclei of rat motoneurons were calculated from reconstruction in araldite embedded spinal cord. The results were compared with those obtained by applying formulae to two-dimensional measurements. The results show that the volumes of reconstructed cells have comparable values when derived from transverse and longitudinal sections. These values differ quite remarkably from those obtained by applying the formulae of the sphere and of a non-rotational ellipsoid. The difference is thought to reflect shape and orientation of the cells in the spinal cord. Nuclei were found to have a spheroidal shape, with the major diameter parallel to the axis of the spinal cord. There is also a linear relationship between cells and nuclear volume (with values varying between 5 and 15). The results of this study suggest that once reconstruction studies have shown the basic parameters of the cells, a graphical method for cell volumes from equatorial area measurements gives more satisfactory results than other proposed methods.

Spinal and cranial motor nerve roots in amyotrophic lateral sclerosis and X-linked recessive bulbospinal muscular atrophy: morphometric and teased-fiber study

Amyotrophic lateral sclerosis (ALS) and adult onset X-linked recessive bulbospinal muscular atrophy (SPMA), constituting the category of adult onset form of motor neuron disease, were analyzed on motor nerve roots. The results of morphometric analysis on ventral spinal roots (VSR) of all spinal segments from ALS and SPMA revealed the following three findings: (1) the large-myelinated alpha-motoneuron fibers were markedly decreased in number throughout all segments; (2) thin-myelinated autonomic preganglionic fibers were almost completely preserved; (3) small-intermediate-myelinated fibers which are considered to correspond to gamma-motoneuron fibers were generally well preserved in ALS, but decreased by one-half to one-third in SPMA. However, all the components of the nerve roots of the oculomotor, trochlear, and abducent nerves were completely preserved in both ALS and SPMA. Moreover, the teased-fiber study showed that the regenerating-sprouting process rarely occurred in the VSR of ALS and SPMA. The present study suggested that the site of the primary lesion seems to be in the alpha-motoneuron fibers in motor neuron diseases, such as ALS or SPMA. However, the marked discrepancy in the pathologic change in the alpha-motoneuron fibers in the VSR and the nerve roots innervating the external ocular muscles was noteworthy.

Morphometric evaluation of primary sensory neurons in experimental p-bromophenylacetylurea intoxication

To evaluate the three-dimensional pathology of lumbar primary sensory neurons in p-bromophenylacetylurea intoxication, the number and size distribution of neurons and of myelinated fibers were evaluated at the L-6 spinal ganglion level and at proximal and distal levels of sural nerve and thoracic (proximal) and cervical (distal) levels of Goll's tract, respectively, 2 and 6 weeks after the intoxication in rats. The number and size distribution of ganglion neuron cell bodies were not significantly different between intoxicated and control rats. The distal level of sural nerve had significantly fewer large myelinated fibers than did control, and a significantly higher frequency of fibers undergoing degeneration. Proximal levels of sural nerve showed similar, but less severe changes. Similarly, the myelinated fibers of Goll's tract were significantly more affected at cervical than at thoracic level. Therefore, by morphometric criteria both centrally and peripherally directed myelinated fibers are most affected distally and less affected proximally while neuron cell bodies are not affected at all. These three-dimensional morphological changes must be taken into consideration in formulating possible mechanisms for the development of this neuropathy.

Renal disease in familial dysautonomia

A study of renal disease in familial dysautonomia identified excess glomerulosclerosis in 10 or 13 autopsied and biopsied patients. Sympathetic nerve terminals could not be found on renal vessels in biopsied tissue; they were invariably demonstrable in controls. Altered renovascular responsivity to systemic hypotension in familial dysautonomia may lead to ischemia and subsequent sclerosis of glomeruli. Review of 79 living outpatients showed that clinically overt renal disease was rare in familial dysautonomia. Nevertheless, frequent observations of elevations of serum creatinine concentrations (32% of patients) and blood urea concentrations (76% of patients) indicated a high prevalence of abnormality. An association was found between hypotension and renal dysfunction.