Neuroaxonal dystrophy with neuromelanin deposition, neurofibrillary tangles, and neuronal loss. Light- and electron-microscopic changes in a 45-year-old woman with progressive psychomotor deterioration

Neurodegeneration with brain iron accumulation

Neurodegeneration with brain iron accumulation (NBIA) describes a heterogeneous group of inherited rare clinical and genetic entities. Clinical core symptoms comprise a combination of early-onset dystonia, pyramidal and extrapyramidal signs with ataxia, cognitive decline, behavioral abnormalities, and retinal and axonal neuropathy variably accompanying these core features. Increased nonphysiologic, nonaging-associated brain iron, most pronounced in the basal ganglia, is often termed the unifying characteristic of these clinically variable disorders, though occurrence and extent can be fluctuating or even absent. Neuropathologically, NBIA disorders usually are associated with widespread axonal spheroids and local iron accumulation in the basal ganglia. Postmortem, Lewy body, TDP-43, or tau pathology has been observed. Genetics have fostered ongoing progress in elucidating underlying pathophysiologic mechanisms of NBIA disorders. Ten associated genes have been established, with many more being suggested as new technologies and data emerge. Clinically, certain symptom combinations can suggest a specific genetic defect. Genetic tests, combined with postmortem neuropathology, usually make for the final disease confirmation. Despite these advances, treatment to date remains mainly symptomatic. This chapter reviews the established genetic defects leading to different NBIA subtypes, highlights phenotypic presentations to direct genetic testing, and briefly discusses the scarce available treatment options and upcoming challenges and future hopes of the field.

Pantothenate kinase-associated neurodegeneration is not a synucleinopathy

Aims: Mutations in the pantothenate kinase 2 gene (PANK2) are responsible for the most common type of neurodegeneration with brain iron accumulation (NBIA), known as pantothenate kinase-associated neurodegeneration (PKAN). Historically, NBIA is considered a synucleinopathy with numerous reports of NBIA cases with Lewy bodies and Lewy neurites and some cases reporting additional abnormal tau accumulation. However, clinicopathological correlations in genetically proven PKAN cases are rare. We describe the clinical, genetic and neuropathological features of three unrelated PKAN cases. Methods: All three cases were genetically screened for the PANK2 gene mutations using standard Sanger polymerase chain reaction sequencing. A detailed neuropathological assessment of the three cases was performed using histochemical and immunohistochemical preparations. Results: All cases had classical axonal swellings and Perls' positive iron deposition in the basal ganglia. In contrast to neuroaxonal dystrophies due to mutation of the phospholipase A2, group VI (PLA2G6) gene, in which Lewy body pathology is widespread, no α-synuclein accumulation was detected in any of our PKAN cases. In one case (20-year-old male) there was significant tau pathology comprising neurofibrillary tangles and neuropil threads, with very subtle tau pathology in another case. Conclusions: These findings indicate that PKAN is not a synucleinopathy and, hence the cellular pathways implicated in this disease are unlikely to be relevant for the pathomechanism of Lewy body disorders.

Tau-predominant-associated pathology in a sporadic late-onset Hallervorden-Spatz syndrome

Hallervorden-Spatz syndrome (HSS) is a heterogeneous clinicopathological disorder currently included within the broader title of neurodegeneration with brain iron accumulation (NBIA). The classic histological hallmarks of HSS are axonal spheroids and excessive iron-containing granules accompanied by neuronal loss and gliosis in the globus pallidus and substantia nigra reticulata. In the modern literature, attention has been drawn to the co-occurrence of two other histological markers: Lewy bodies mainly composed of abnormal alpha-synuclein, and neurofibrillary tangles due to hyperphosphorilated tau aggregation. Discrepancies exist regarding the importance of these molecular changes and its relevance for the nosology of HSS. Most authors have emphasized the importance of the Lewy body-like pathology, favoring the inclusion of HSS within the alpha-synucleinopathies. We report on a case of late-onset HSS, with the typical histological findings restricted to the basal ganglia and cerebellum in which tau pathology was exceedingly more abundant than alpha-synuclein pathology. This case contributes to the increasing evidence about the heterogeneity of HSS. We favor the view that the molecular changes and the protein misfolding underlying the Lewy body and tangle formation in HSS/NBIA are secondary to the main pathological process and should not be taken as the basis for its nosological classification.

Ovine neuroaxonal dystrophy in New Zealand

A condition of neuroaxonal dystrophy of Coopworth sheep is described. This was characterised clinically by progressive ataxia from weaning with collapse of hindquarters and ultimately death. One per cent to 10% of the lamb flock on three commerical farms were affected over several years. Histopathological features were bilateral spheroid formation in specific brain stem nuclei and in the dorsal horn (especially in and about Clarke's column) along the length of the spinal cord. The condition appears virtually identical to that recorded earlier in Californian Suffolk sheep and that seen previously in the Romney, Perendale and Coopworth breeds in New Zealand. The cause was undetermined but it is suggested there may be an inherited component, as has been postulated in the Suffolks.

Widespread expression of alpha-synuclein and tau immunoreactivity in Hallervorden-Spatz syndrome with protracted clinical course

Hallervorden-Spatz syndrome (HSS) is a rare autosomal recessive disorder clinically characterized by extrapyramidal signs and progressive dementia. In a typical case, the clinical symptoms become apparent during late childhood, and usually the course is protracted over a decade or more. We recently had an opportunity to study the brains of two cases of HSS with a clinical course of over 30 years. Case 1 was a 44-year-old female and case 2 was a 37-year-old male. Grossly, the brains showed severe fronto-temporal lobar atrophy with abundant spheroids and mild iron deposits in the globus pallidus, associated with features of motor neuron disease. In addition, there was diffuse sponginess in the atrophic cortex as well as widespread Alzheimer's neurofibrillary tangles (NFTs) and Lewy bodies (LBs) in the cortical and subcortical regions, including the spinal cord. Ultrastructurally, NFTs were composed of paired helical filaments, and LBs of central dense cores with radiating fibrils. Discrete immunostaining was demonstrated in NFTs and neuropil threads with various antibodies against phosphorylated tau, and in LBs with antibody against alpha-synuclein. In addition, diffuse, overlapping immunoreactivity of alpha-synuclein and phosphorylated tau was seen within the cytoplasm of many neurons. However, when LBs and NFTs coexisted within the same neurons, they were clearly segregated. The findings of our present cases as well as those reported in the literature may indicate that simultaneous and extensive occurrence of abnormal phosphorylation of tau and accumulation of alpha-synuclein may constitute cardinal pathological features of HSS with protracted clinical course.

The nosology of Hallervorden-spatz disease

The development of magnetic resonance imaging has increased the number of clinical and pathological reports of Hallervorden-Spatz disease and Hallervorden-Spatz syndrome. The case-to-case variability is considerable. However, if gene loci and basic pathogenetic mechanisms are to be appreciated, it is imperative that like cases be compared and studied. The designation Hallervorden-Spatz disease should be reserved for the pediatric neurodegenerative disorder, recognizing that it occurs either as a familial or a sporadic disorder. The diagnosis of Hallervorden-Spatz syndrome is non-specific and encompasses a number of distinctive disorders, each having the pallidal triad of iron deposition, axonal spheroids, and gliosis. Clinically or pathologically distinct groups include (a) female patients with dementia, quadriparesis, and neurofibrillary tangles; (b) cases with Lewy bodies; and (c) cases with or without lipid abnormalities which have acanthocytosis and pigmentary retinal degeneration. Adult-onset cases are quite variable, both clinically and pathologically. Iron deposition in the globus pallidus separates these disorders from others in which axonal spheroids occur. Undoubtedly, the pallidal changes are related, some being primary and other possibly epiphenomena. Pathogenetic insights can only be achieved by investigating and comparing like cases.

Diagnosis of juvenile-adult form of neuroaxonal dystrophy by electron microscopy of rectum and skin biopsy

Images

Cerebellar abiotrophy and segmental axonopathy: two syndromes of progressive ataxia of Merino sheep

Findings of a study of 39 sheep with progressive ataxia from 14 farms in the Yass district of New South Wales are described. Microscopic lesions in 25 sheep, 3.5 to 6 years of age, diagnosed as having clinical cerebellar disease, consisted of an apparent primary loss of cerebellar Purkinje neurons, and glial cell accumulation. It is suggested that this previously unreported disorder may be an hereditary cerebellar abiotrophy of Merino sheep. A further 14 sheep, 1 to 4 years of age, had distinguishable clinical signs referable to a spinal cord lesion with widespread segmental axonal ballooning, or "spheroids", in the white matter of the brain and spinal cord. It is suggested that these sheep have a unique form of neuroaxonal dystrophy, described here as segmental axonopathy, and that this is likely to be the same condition described previously as Murrurindi disease (Hartley and Loomis 1981).

Communicating hydrocephalus in rodents treated with beta,beta'-iminodipropionitrile (IDPN)

Beta,beta'-Iminodipropionitrile (IDPN), a neurotoxic compound known to induce swellings in the proximal internodes of sensory and motor axons in several parts of the central nervous system (CNS), was also found to cause hydrocephalus in rats and guinea pigs. In both species, ventricular dilatation was observed within 1 week following a single i.p. injection of IDPN. While in rats the severity of hydrocephalus correlated with dose and duration of IDPN exposure, in guinea pigs studies with high doses yielded inconclusive results, and no significant temporal correlation was noted. Parallel investigations with another neurotoxic agent, acrylamide, in rats, and with IDPN in cats failed to demonstrate any change in size and shape of the cerebrospinal fluid (CSF) pathways. No signs of spontaneously occurring hydrocephalus were found in control animals. In both rats and guinea pigs intoxicated with IDPN, macroscopic and microscopic findings were consistent with the diagnosis of communicating hydrocephalus. Treatment of hydrocephalic rats with acetazolamide (500 mg/kg) markedly attenuated ventricular distention, suggesting that an overproduction of CSF by the choroid plexus is responsible for the communicating hydrocephalus following IDPN intoxication.