Pathology of skeletal muscle and intramuscular nerves in infantile neuroaxonal dystrophy

Disorders of metal metabolism

Trace elements are chemical elements needed in minute amounts for normal physiology. Some of the physiologically relevant trace elements include iodine, copper, iron, manganese, zinc, selenium, cobalt and molybdenum. Of these, some are metals, and in particular, transition metals. The different electron shells of an atom carry different energy levels, with those closest to the nucleus being lowest in energy. The number of electrons in the outermost shell determines the reactivity of such an atom. The electron shells are divided in sub-shells, and in particular the third shell has s, p and d sub-shells. Transition metals are strictly defined as elements whose atom has an incomplete d sub-shell. This incomplete d sub-shell makes them prone to chemical reactions, particularly redox reactions. Transition metals of biologic importance include copper, iron, manganese, cobalt and molybdenum. Zinc is not a transition metal, since it has a complete d sub-shell. Selenium, on the other hand, is strictly speaking a nonmetal, although given its chemical properties between those of metals and nonmetals, it is sometimes considered a metalloid. In this review, we summarize the current knowledge on the inborn errors of metal and metalloid metabolism.

Inherited Paediatric Motor Neuron Disorders: Beyond Spinal Muscular Atrophy

Paediatric motor neuron diseases encompass a group of neurodegenerative diseases characterised by the onset of muscle weakness and atrophy before the age of 18 years, attributable to motor neuron loss across various neuronal networks in the brain and spinal cord. While the genetic underpinnings are diverse, advances in next generation sequencing have transformed diagnostic paradigms. This has reinforced the clinical phenotyping and molecular genetic expertise required to navigate the complexities of such diagnoses. In turn, improved genetic technology and subsequent gene identification have enabled further insights into the mechanisms of motor neuron degeneration and how these diseases form part of a neurodegenerative disorder spectrum. Common pathophysiologies include abnormalities in axonal architecture and function, RNA processing, and protein quality control. This review incorporates an overview of the clinical manifestations, genetics, and pathophysiology of inherited paediatric motor neuron disorders beyond classic SMN1-related spinal muscular atrophy and describes recent advances in next generation sequencing and its clinical application. Specific disease-modifying treatment is becoming a clinical reality in some disorders of the motor neuron highlighting the importance of a timely and specific diagnosis.

A case of infantile neuroaxonal dystrophy: connatal Seitelberger disease

We present a male stillbirth with infantile neuroaxonal dystrophy (connatal Seitelberger disease). Following the development of polyhydramnios with an ultrasound scan showing severe distal arthrogryposis, the mother was induced at 38 weeks. A moderately macerated severely intrauterine growth restricted male stillbirth was delivered. External microcephaly, sloping forehead, simplified palmar skin creases, fixed flexion deformities of the knees, severe talipes equinovarus, spinal scoliosis, and empty scrotum were present. The brain was microcephalic with normal gyration, having a hypoplastic corpus callosum, thinned insular cortex, and enlarged lateral ventricles. There was a progressive increase in axonal spheroids going in a rostrocaudal direction in the central nervous system with the preferential distal denervation of muscles, with their motor nerves showing axonal spheroids. The presence of axonal spheroids in both the central and peripheral nervous systems and electron microscopic appearances were diagnostic of infantile neuroaxonal dystrophy occurring in utero.

[Infantile neuroaxonal dystrophy: report of 2 cases]

We describe two cases of infantile neuroaxonal dystrophy, which is a rare, neurodegenerative disease, with autosomal recessive inheritance. The first case was an 8 year old boy, with arrested motor and mental development, ataxia and muscle weakness. On physical examination there was horizontal and vertical nystagmus, optic disc atrophy, hypotonia; deep tendon reflexes were absent. The second case was a 1.6 year old boy with arrested motor and mental development, and seizures. On physical examination there was optic atrophy, hypertonia and hyperreflexia. Both patients had on sural nerve biopsy neuronal enlargement, consistent with neuroaxonal dystrophy. Diagnosis without pathological confirmation with neuroaxonal spheroids is very difficult, because the clinical picture is variable and the neurophysiological findings are non specific.

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.

[Peripheral neuropathies in childhood: a neuropathological approach]

Peripheral neuropathies affect children more often than the young and middle age adults, but less frequently than the elderly. They differ from those in the adults because of the high incidence of hereditary neuropathies, including those associated with metabolic and degenerative disorders of the central nervous system; the low incidence of toxic neuropathies and those associated with systemic disorders; and a lower incidence of chronic acquire polineuropathies. Nerve biopsies are indicated if the diagnosis has not been made with clinical and electrophysiologic studies and other methods, and should only be performed in laboratories with appropriated techniques for the study of the nerve. It is important to know the normal development of the nerve, the thickness of the myelin sheath and the distribution of small and large fibers, according to the age. The main morphological aspects of the most frequent neuropathies in children--acquired (inflammatory, demyelinating) and hereditary (sensory-motor, sensory-autonomic, ataxic, and those associated with metabolic and degenerative disorders), are reviewed.

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).

Ultrastructural muscle pathology in infantile neuroaxonal dystrophy

Ultrastructural examination of muscle in infantile neuroaxonal dystrophy (INAD) revealed intramuscular cytoplasmic bodies, fibrous bodies and concentric laminated bodies. Although these intramuscular inclusions have been reported in various conditions and thus are considered to be non-specific changes, this is the first report of observing them in INAD.

Intramuscular nerves in motor neurone disease. A quantitative ultrastructural study

The ultrastructure of human intramuscular nerves at biopsy has been compared in motor neurone disease with that in other neuromuscular disease including muscular dystrophy and in controls. Myelinated axons appeared to be lost in control patients aged over 50 years, but this varied both between and within nerve fascicles. Even in two boys aged 3 1/2 and 9 years, but with Duchenne's dystrophy, examples were found of nerve fascicles with few or no axons. In motor neurone disease additional nerve fibres were lost, but there was little change in the size distributions of axons and myelin sheaths within the muscle. In both preterminal and terminal fascicles there was an increase of Schwann cell cytoplasm in association with unmyelinated axons, which was compatible with nerve sprouting. It is concluded that intramuscular nerves are likely to be lost with age as well as motor neurone disease. The results are discussed in relation to the stage of the disease process at biopsy.

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.