Infantile neuroaxonal dystrophy. Ultrastructural study of peripheral nerve

Spontaneous murine neuroaxonal dystrophy: a model of infantile neuroaxonal dystrophy

The neuroaxonal dystrophies (NADs) in human beings are fatal, inherited, neurodegenerative diseases with distinctive pathological features. This report describes a new mouse model of NAD that was identified as a spontaneous mutation in a BALB/c congenic mouse strain. The affected animals developed clinical signs of a sensory axonopathy consisting of hindlimb spasticity and ataxia as early as 3 weeks of age, with progression to paraparesis and severe morbidity by 6 months of age. Hallmark histological lesions consisted of spheroids (swollen axons), in the grey and white matter of the midbrain, brain stem, and all levels of the spinal cord. Ultrastructural analysis of the spheroids revealed accumulations of layered stacks of membranes and tubulovesicular elements, strongly resembling the ultrastructural changes seen in the axons of human patients with endogenous forms of NAD. Mouse NAD would therefore seem a potentially valuable model of human NADs.

Floppy infant syndrome

Floppiness/hypotonia is a common neurologic symptom in infancy. A variety of neuromuscular disorders and central nervous system (CNS) disorders cause floppy infant syndrome (FIS). CNS disorders are the much more common causes of the syndrome than neuromuscular disorders. On long-term follow up, cerebral palsy and mental retardation turn out to be the 2 most common causes of FIS. This review focuses on neuromuscular causes of FIS. With the advent of molecular diagnosis, a few conditions can be diagnosed by DNA analysis of the peripheral lymphocytes (myotonic dystrophy, spinal muscular atrophy); however, for the most part, electrodiagnostic studies and muscle biopsy remain as essential diagnostic tools for FIS. Immunohistochemical study of the biopsied muscle also improves diagnostic capability. Management for most conditions remains supportive.

A novel chronic childhood sensory predominant neuropathy

Chronic childhood neuropathies are predominantly hereditary in origin. Specific distinct clinical entities have been described, however, occasionally children with an unusual clinical phenotype are encountered in practice. We describe four children (3 males, 1 female) of Lebanese Moslem descent all sharing a common great-great-grandparent pairing with such a novel clinical spectrum. The three males were first cousins, each the product of a different parental consanguineous (i.e., parents second cousins) mating, whereas the female was a third cousin to each of the males whose parents were also second cousins. Each child presented early in life with developmental delay with associated hypotonia and areflexia. All had a sensorineural hearing loss documented and two of the patients were dysmorphic in facial appearance. Nerve conduction studies highlighted a sensory axonal neuropathy and sural nerve biopsy undertaken in two patients confirmed an axonal neuropathy. Detailed genetic and metabolic testing was negative. Followed into later childhood, each child continued to manifest motoric impairment, unsteadiness, areflexia, and cognitive disability. These children appear to provide evidence for a novel autosomal recessive inherited chronic predominantly sensory neuropathy that shares core clinical features with observed variability in associated symptoms.

Infantile neuroaxonal dystrophy: clinical spectrum and diagnostic criteria

OBJECTIVE

To present clinical, neurophysiologic, and neuroradiologic findings in 13 patients with infantile neuroaxonal dystrophy (INAD), focusing on aspects that assist early diagnosis.

BACKGROUND

Clinicopathologic diagnostic criteria for INAD were delineated by Aicardi and Castelein in 1979, but atypical cases are reported frequently and little is known of the diagnostic utility of MRI.

METHODS

The authors reviewed the clinical, neurophysiologic, and MRI findings of 13 patients who met the diagnostic criteria for INAD.

RESULTS

Symptoms onset was between 6 months and 2 years of age. In nine patients the clinical course was typical, with rapid motor and mental deterioration; in four patients progression was slower and the clinical picture was different. Electromyographic (EMG) signs of chronic denervation, fast rhythms on EEG and abnormal visual evoked potentials were observed in all patients during the disease course. Cerebellar atrophy with signal hyperintensity in the cerebellar cortex on T2-weighted images were the most characteristic MRI findings; hypointensity in the pallida and substantia nigra was also observed in two patients. alpha-N-acetyl-galactosaminidase activity on leukocytes was normal in the 10 patients tested.

CONCLUSIONS

EMG and MRI abnormalities are the earliest and most suggestive signs of INAD, which has a clinical and radiologic spectrum that is broader than reported previously.

Mechanism of calcium entry during axon injury and degeneration

Axon degeneration is a hallmark consequence of chemical neurotoxicant exposure (e.g., acrylamide), mechanical trauma (e.g., nerve transection, spinal cord contusion), deficient perfusion (e.g., ischemia, hypoxia), and inherited neuropathies (e.g., infantile neuroaxonal dystrophy). Regardless of the initiating event, degeneration in the PNS and CNS progresses according to a characteristic sequence of morphological changes. These shared neuropathologic features suggest that subsequent degeneration, although induced by different injury modalities, might evolve via a common mechanism. Studies conducted over the past two decades indicate that Ca2+ accumulation in injured axons has significant neuropathic implications and is a potentially unifying mechanistic event. However, the route of Ca2+ entry and the involvement of other relevant ions (Na+, K+) have not been adequately defined. In this overview, we discuss evidence for reverse operation of the Na+-Ca2+ exchanger as a primary route of Ca2+ entry during axon injury. We propose that diverse injury processes (e.g., axotomy, ischemia, trauma) which culminate in axon degeneration cause an increase in intraaxonal Na+ in conjunction with a loss of K+ and axolemmal depolarization. These conditions favor reverse Na+-Ca2+ exchange operation which promotes damaging extraaxonal Ca2+ entry and subsequent Ca2+-mediated axon degeneration. Deciphering the route of axonal Ca2+ entry is a fundamental step in understanding the pathophysiologic processes induced by chemical neurotoxicants and other types of nerve damage. Moreover, the molecular mechanism of Ca2+ entry can be used as a target for the development of efficacious pharmacotherapies that might be useful in preventing or limiting irreversible axon injury.

Neuroaxonal dystrophy in infantile alpha-N-acetylgalactosaminidase deficiency

Morphologic alterations in biopsies of central and peripheral nervous tissue were investigated at the light-and electron-microscopic level in the first cases of lysosomal alpha-N-acetylgalactosaminidase deficiency. Widespread spheroid formation was observed in terminal and preterminal axons. Neocortical and peripheral autonomic axons contained tubulovesicular and lamelliform membranous arrays, prominent acicular clefts, and electron-dense axoplasmic matrix, the typical ultrastructural abnormalities corresponding to axonal spheroids in many inherited and acquired axonopathies. Central and peripheral membranous distal axonal spheroids were the only neuropathologic abnormality identified; other alterations resembling those in various neuronopathic lysosomal storage diseases were not observed. The morphologic findings and the distribution of the lesion in the present disorder are remarkably similar to those reported in the inherited infantile form of neuroaxonal dystrophy with normal alpha-N-acetylgalactosaminidase activity (Seitelberger disease).

MRI in infantile neuroaxonal dystrophy

A 6-year-old boy with the typical clinical features of infantile neuroaxonal dystrophy was examined with magnetic resonance imaging. The findings suggested increased metal deposition in the globus pallidus. Magnetic resonance imaging findings of Hallervorden-Spatz syndrome and infantile neuroaxonal dystrophy are similar, suggesting that these two disease entities overlap. Magnetic resonance imaging findings, as well as relevant clinical features, may be useful in the diagnosis and classification of infantile neuroaxonal dystrophy.

Myenteric plexus neuropathy in infantile hypertrophic pyloric stenosis

The myenteric plexus and intramuscular nerve bundles in the circular muscle layer of the pylorus from 37 children with infantile hypertrophic pyloric stenosis (IHPS) obtained at pyloromyotomy were studied by light and electron microscopy and compared to six control cases without clinical evidence of IHPS. In certain IHPS cases degenerative alterations of the axons predominated. The axonal changes consisted of (1) severely increased variability of diameters with evidence of degeneration and regeneration of some axons, (2) accumulation of electron-dense bodies, lysosomes and pleomorphic membranous cytoplasmic bodies, (3) increase in the number of maloriented neurofilaments, and (4) aggregation of glycogen granules. Degenerative changes or immaturity of perikarya of neurons and glial cells in the myenteric plexus were not a significant feature. While axonal changes predominated in some IHPS cases there were severe changes of smooth muscle cells in others suggesting that a primarily neurogenic type of IHPS can be distinguished from a predominantly myogenic type. Although the etiology of the axonal changes in IHPS is not clear, it is suggested that they play an important role in the pathogenesis of pyloric stenosis and hypertrophy.

Axonal pathology of the skin in infantile neuroaxonal dystrophy

Ultrastructural studies on the skin of two patients affected by infantile neuroaxonal dystrophy (INAD) were performed to evaluate its diagnostic value and to discuss the etiology of INAD. While the majority of terminal axons around intradermal glands were dystophic consisting of tubulomembranous and tubulovesicular profiles sometimes accompanied by synaptic vesicles, there were only few dystophic axons inside intradermal nerve bundles. These observations suggest that the primary lesion of INAD is located in terminal and presynaptic axons. Therefore, terminal axons have to be investigated when a diagnostic skin biopsy is performed in INAD.

Pathology of skeletal muscle and intramuscular nerves in infantile neuroaxonal dystrophy

Biopsies of the biceps muscle and sural nerve were taken from a girl aged 2 years with infantile neuroaxonal dystrophy (INAD). In addition to the typical axonal spheroid bodies in a number of the i.m. nerve fibers, the neuromuscular junctions (NMJs) and motor nerve endings also contained axonal swellings. The sural nerve, except for three dystrophic fibers, was almost completely normal. A teased nerve preparation showed four additional abnormal fibers with focal axonal enlargement similar to those in giant axonal neuropathy (GAN). These results suggest that a biceps muscle biopsy may be more useful than a sural nerve biopsy for the diagnosis of INAD, because the muscle contains abnormal peripheral nerves and NMJs in high frequency.

'Acrylamide-induced' neuropathy and impairment of axonal transport of proteins. II. Abnormal accumulations of smooth endoplasmic reticulum as sites of focal retention of fast transported proteins. Electron microscope radioautographic study

The distribution of fast axonally transported proteins was studied by electron microscope radioautography in ciliary ganglia of chickens treated or not treated with acrylamide. At 3 h after the intracerebral injection of [3H]lysine, the preganglionic axons of the untreated chickens displayed few silver grains, mainly associated with smooth endoplasmic reticulum (SER) profiles. In most axons of acrylamide-treated chickens, a similar pattern was observed, except in axons which exhibited focal and intense labeling underneath the axolemma: clusters of silver grains indeed overlayed peripheral accumulations of tubulovesicular profiles of SER, dense core vesicles and mitochondria. After impregnation with heavy metals, electron microscope observation of 1 micrometer thick sections showed a locally disorganized SER forming a complex network of tubules intermingled with vesicles and mitochondria. Such a local disorganization of the peripheral SER in the distal part of the axons, could be responsible for the focal stasis of fast transported proteins; it seems to be one of the earliest changes detectable in axons damaged by acrylamide treatment.

Axoplasmic transport in zinc pyridinethione neuropathy: evidence for an abnormality in distal turn-around

Axoplasmic transport studies were done in rats with a zinc pyridinethione-induced dying-back neuropathy characterized by the accumulation of branched interconnected tubulovesicular profiles in the motor nerve terminals. Fast anterograde transport studies in sensory and motor systems were significantly reduced compared to controls but there was a wide variation in results and a lack of correlation with clinical involvement. Retrograde transport studies showed a delay in the time of onset and a reduction in the amount of retrograde transported materials. Analysis of the integrals of retrograde transport indicated that the defect was related to a failure in the turn-around process in the distal axon as opposed to a decreased rate of retrograde transport. Similar changes were not present in the proximal morphologically normal portion of the axon where retrograde transport was provoked with a crush injury.

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.

Skin and conjunctival biopsies in infantile neuroaxonal dystrophy

The diagnosis of infantile neuro-axonal dystrophy (INAD) in a 5-year-old patient was confirmed by the ultrastructural study of neuromuscular, skin and conjunctival biopsy specimens. Abnormal networks of smooth membranous, lamellar and tubular profiles were found in presynaptic terminals and in conjunctival and dermal axons. INAD is the first neurological disease outside the group of storage disorders in which skin and conjunctival biopsies contribute significiantly to the diagnosis.

Morphological investigations on axonal swellings and spheroids in various human diseases

Axonal swellings and spheroids in various human diseases were studied by light and electron microscopy. 4 cases of infantile neuroaxonal dystrophy, 2 of degenerative diseases, 2 brain tumors and 3 of cerebrovascular disease were examined. Ultrastructurally most spheroids in infantile neuroaxonal dystrophy consisted of interconnected tubules, stacked membranotubular profiles, alternating layered membranes and accumulations of neurofilaments. Combinations of these four constituents were seen only in infantile neuroaxonal dystrophy. "Torpedos" (fusiform swelling of the axon of a Purkinje cell) consisted exclusively of neurofilaments. Spheroids in case 6 (mental retardation) and 7 (atypical teratoma) consisted of interwoven skeins of neurofilaments and grouped mitochondria. Spheroids in case 8 (demyelination) and 9 (cerebrovascular disease) consisted of packed complex bodies and mitochondria. Spheroids in cases 10 and 11 (cerebrovascular disease) consisted of degenerating organelles only. The morphological differences between cases 9, 10 and 11 probably depends on the severity and timing of the cerebral injury. Most spheroids show similar histological and histochemical properties, but ultrastructural study may give some clue to the origin of the bodies.

Diagnosis of infantile neuroaxonal dystrophy by conjunctival biopsy

Conjunctival biopsy and ultrastructural examination of conjunctival nerves, showing the presence of spheroids within axons, led to the confirmation of the diagnosis of infantile neuroaxonal dystrophy in two children with progressive mental deterioration. Conjunctival biopsy, which is simple to perform, even in young children, and does not require general anaesthesia or admission to hospital, is presented as a reliable and very convenient technique for the diagnosis of infantile neuroaxonal dystrophy.

Brain biopsies for neurodegenerative disease in children

Brain biopsies for neurodegenerative disease performed at The Hospital for Sick Children, Toronto, over a 12-year period (1964 to 1976) were reviewed. Of 64 biopsies, major histologic abnormalities with diagnostic or prognostic significance comprised 39% of the total cases, minor abnormalities represented 13%, and 48% appeared normal. The procedure failed to provide prognostic assistance in 41%. With the advent for newer diagnostic techniques (enzyme assays and muscle, skin, peripheral nerve, rectal, and appendix biopsies) for neurodegenerative disease in childhood, a much lower yield is noted (15 to 20%). Only two progressive degenerative childhood conditions remain in which cerebral tissue is necessary for diagnosis--Alexander disease and Canavan spongy degeneration.

Infantile neuroaxonal dystrophy. Schwann cell inclusion in the peripheral nerve

Abnormal Schwann cell inclusion is reported in biopsied peripheral nerve in a case of infantile neuroaxonal dystrophy. In addition to non-specific dystrophic changes of the axons, the Schwann cells contained several distinct bodies which were composed of stacks of irregularly disposed membranes; in some instances, transformed Schwann cell cytoplasm was distined with similar bodies. This change has not been reported on this condition and its significance is briefly discussed.

Generalized giant axonal neuropathy: a filament-forming disease of neuronal, endothelial, glial, and schwann cells in a patient without kinky hair

The process of Giant Axonal Neuropathy (GAN) is not restricted to the peripheral nerves, but also involves the central nervous system. In a 25 year old man with normal hair, abundant axon swellings and spheroids were observed in the spinal cord, brain system, and cerebral cortex. The findings in the sural nerve have already been published by Boltshauser et al. (1977). Accumulations of filaments in the axons and in the perineural cells were accompanied by Rosenthal fibres. The ultrastructural pattern of GAN differs clearly from that of Neuroaxonal Dystrophies.

Spastic paraplegia with neurogenic amyotrophy manifesting ballooned axons in sural nerve

A 21-year-old man had progressive symmetric, distal muscle atrophy and weakness, as well as spasticity of the limbs. Histologic examination of the sural nerve disclosed swollen axons containing membranous tubular profiles, ring tubules, large mitochondria with abnormal cristae, and glycogen like granules. Peripheral sensory nerve fibers also were affected. The pathologic features of the peripheral nerves were similar to those of infantile neuroaxonal dystrophy. Sural nerve biopsy may be useful in the study of pathologic processes in spastic paraplegia.