Degeneration of olivospinal tract in the upper cervical spinal cord of multiple system atrophy patients: Reappraisal of Helweg's triangular tract

Multiple system atrophy (MSA) is an adult-onset neurodegenerative disorder that presents with variable combinations of autonomic dysfunction, cerebellar ataxia, parkinsonism, and pyramidal signs. The inferior olivary nucleus is targeted in MSA, with a phenotype of olivopontocerebellar atrophy in particular, and involvement of the olivocerebellar tract is well known. However, degeneration of the olivospinal tract has not been studied in MSA. We examined 97 spinal cords from consecutively autopsied patients with MSA. Myelin staining revealed that 22 cords (22.7%) had small, bilateral, triangular-shaped tract degeneration in the boundary of the anterior and lateral funiculi, which appeared continuously from C1 to C5. The anatomical pathway of the degenerated tract was consistent with the description of the olivospinal tract provided by Helweg in 1888. The MSA patients showing degeneration of this tract were younger at disease onset (average: 56.4 ± 8.7 years, range: 42-74), and had longer disease duration (average: 10.1 ± 4.8 years, range: 2-25) and more severe olivopontocerebellar changes compared to other MSA patients. Quantitative analyses revealed that patients with olivospinal tract degeneration had a lower neuronal density in the inferior olivary nucleus compared to other patients. Microglial density in this tract was negatively correlated with the neuronal density in the inferior olivary nucleus. The densities of glial cytoplasmic inclusions in the inferior olivary nucleus and in the olivospinal tract were strongly correlated with each other. Neurologically healthy controls (n = 22) and disease controls with Lewy body disease (n = 30), amyotrophic lateral sclerosis (n = 30), and progressive supranuclear palsy (n = 30) did not present the olivospinal tract degeneration. Our results indicate an impairment of the neural connection between the inferior olivary nucleus and the spinal cord in MSA patients, which may develop in a descending manner.

Clinical and genetic analysis of infants with pontocerebellar hypoplasia type 6 caused by RARS2 variations

OBJECTIVE

Defects in RARS2 cause cerebellopontine hypoplasia type 6 (pontocerebellar hypoplasia type 6, PCH6, OMIM: #611523), a rare autosomal recessive inherited mitochondrial disease. Here, we report two male patients and their respective family histories.

METHODS

We describe the clinical presentation and magnetic resonance imaging (MRI) findings of these patients. Whole-exome sequencing was used to identify the genetic mutations.

RESULTS

One patient showed hypoglycemia, high lactic acid levels (fluctuating from 6.7 to 14.1 mmol/L), and frequent seizures after birth, with progressive atrophy of the cerebrum, cerebellum, and pons. The other patient presented with early infantile developmental and epileptic encephalopathies (EIDEEs) with an initial developmental delay followed by infantile epileptic spasm syndrome (IESS) at 5 months old, with no imaging changes. Whole-exome sequencing identified compound heterozygous RARS2 variants c.25A>G (p.I9V) with c.1261C>T (p.Q421*) and c.1A>G (p.M1V) with c.122A>G (p.D41G) in these two patients. Of these loci, c.1261C>T and c.122A>G have not been previously reported.

SIGNIFICANCE

Our findings have expanded the RARS2 gene variant spectrum and present EIDEEs and IESS as phenotypes which deepened the association between PCH6 and RARS2.

PLAIN LANGUAGE SUMMARY

Defects in RARS2 cause cerebellopontine hypoplasia type 6, a rare autosomal recessive inherited mitochondrial disease. Two patients with RARS2 variants were reported in this article. One patient showed hypoglycemia, high lactic acid levels, and frequent seizures after birth, with progressive atrophy of the cerebrum, cerebellum, and Page 3 of 21 Epilepsia OpenFor Review Only pons. The other patient presented with an initial developmental delay followed by refractory epilepsy at 5 months old, with no imaging changes. Our findings deepened the association between PCH6 and RARS2.

Widespread alternative splicing dysregulation occurs presymptomatically in CAG expansion spinocerebellar ataxias

The spinocerebellar ataxias (SCAs) are a group of dominantly inherited neurodegenerative diseases, several of which are caused by CAG expansion mutations (SCAs 1, 2, 3, 6, 7 and 12) and more broadly belong to the large family of over 40 microsatellite expansion diseases. While dysregulation of alternative splicing is a well defined driver of disease pathogenesis across several microsatellite diseases, the contribution of alternative splicing in CAG expansion SCAs is poorly understood. Furthermore, despite extensive studies on differential gene expression, there remains a gap in our understanding of presymptomatic transcriptomic drivers of disease. We sought to address these knowledge gaps through a comprehensive study of 29 publicly available RNA-sequencing datasets. We identified that dysregulation of alternative splicing is widespread across CAG expansion mouse models of SCAs 1, 3 and 7. These changes were detected presymptomatically, persisted throughout disease progression, were repeat length-dependent, and were present in brain regions implicated in SCA pathogenesis including the cerebellum, pons and medulla. Across disease progression, changes in alternative splicing occurred in genes that function in pathways and processes known to be impaired in SCAs, such as ion channels, synaptic signalling, transcriptional regulation and the cytoskeleton. We validated several key alternative splicing events with known functional consequences, including Trpc3 exon 9 and Kcnma1 exon 23b, in the Atxn1154Q/2Q mouse model. Finally, we demonstrated that alternative splicing dysregulation is responsive to therapeutic intervention in CAG expansion SCAs with Atxn1 targeting antisense oligonucleotide rescuing key splicing events. Taken together, these data demonstrate that widespread presymptomatic dysregulation of alternative splicing in CAG expansion SCAs may contribute to disease onset, early neuronal dysfunction and may represent novel biomarkers across this devastating group of neurodegenerative disorders.

PolyQ Database-an integrated database on polyglutamine diseases

Polyglutamine (polyQ) diseases are neurodegenerative disorders caused by abnormally expanded Cytosine, Adenine, Guanine (CAG) triplet repeat sequences in the coding region of otherwise unrelated genes. Until now, nine different polyQ diseases have been described: Huntington's disease, dentatorubral-pallidoluysian atrophy, spinal and bulbar muscular atrophy and six types of spinocerebellar ataxias-1, 2, 3, 6, 7 and 17. The pathogenic expansion translates into an aberrant tract of glutamines in the encoded proteins, compromising several cellular functions and biological processes. There is currently no cure available for the progressive neurodegenerative disorders caused by the ensuing cytotoxic alterations. Although each disease is considered rare, polyQ diseases constitute the largest group of monogenic neurodegenerative disorders. Information about these disorders is scattered among several books, articles and general databases, hindering exploration by students and researchers, but also by patients and their families. Therefore, we aimed to develop a free online database to fill this gap, by centralizing relevant available information. The PolyQ Database is a platform that focuses on all nine polyQ diseases and offers information about topics that are pertinent for scientists, clinicians and the general public, including epidemiology, the characteristics of the causative genes and the codified proteins, the pathophysiology of the diseases and the main clinical manifestations. The database is available at https://polyq.pt/, and it is the first of its kind, focusing exclusively on this group of rare diseases. The database was conceived to be continuously updated and allow incorporation and dissemination of the latest information on polyQ diseases.

Common Variants Near ZIC1 and ZIC4 in Autopsy-Confirmed Multiple System Atrophy

BACKGROUND

Multiple System Atrophy is a rare neurodegenerative disease with alpha-synuclein aggregation in glial cytoplasmic inclusions and either predominant olivopontocerebellar atrophy or striatonigral degeneration, leading to dysautonomia, parkinsonism, and cerebellar ataxia. One prior genome-wide association study in mainly clinically diagnosed patients with Multiple System Atrophy failed to identify genetic variants predisposing for the disease.

OBJECTIVE

Since the clinical diagnosis of Multiple System Atrophy yields a high rate of misdiagnosis when compared to the neuropathological gold standard, we studied only autopsy-confirmed cases.

METHODS

We studied common genetic variations in Multiple System Atrophy cases (N = 731) and controls (N = 2898).

RESULTS

The most strongly disease-associated markers were rs16859966 on chromosome 3, rs7013955 on chromosome 8, and rs116607983 on chromosome 4 with P-values below 5 × 10-6 , all of which were supported by at least one additional genotyped and several imputed single nucleotide polymorphisms. The genes closest to the chromosome 3 locus are ZIC1 and ZIC4 encoding the zinc finger proteins of cerebellum 1 and 4 (ZIC1 and ZIC4).

INTERPRETATION

Since mutations of ZIC1 and ZIC4 and paraneoplastic autoantibodies directed against ZIC4 are associated with severe cerebellar dysfunction, we conducted immunohistochemical analyses in brain tissue of the frontal cortex and the cerebellum from 24 Multiple System Atrophy patients. Strong immunohistochemical expression of ZIC4 was detected in a subset of neurons of the dentate nucleus in all healthy controls and in patients with striatonigral degeneration, whereas ZIC4-immunoreactive neurons were significantly reduced inpatients with olivopontocerebellar atrophy. These findings point to a potential ZIC4-mediated vulnerability of neurons in Multiple System Atrophy. © 2022 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Loss of Piccolo Function in Rats Induces Cerebellar Network Dysfunction and Pontocerebellar Hypoplasia Type 3-like Phenotypes

Piccolo, a presynaptic active zone protein, is best known for its role in the regulated assembly and function of vertebrate synapses. Genetic studies suggest a further link to several psychiatric disorders as well as Pontocerebellar Hypoplasia type 3 (PCH3). We have characterized recently generated Piccolo KO (Pclogt/gt ) rats. Analysis of rats of both sexes revealed a dramatic reduction in brain size compared with WT (Pclowt/wt ) animals, attributed to a decrease in the size of the cerebral cortical, cerebellar, and pontine regions. Analysis of the cerebellum and brainstem revealed a reduced granule cell layer and a reduction in size of pontine nuclei. Moreover, the maturation of mossy fiber afferents from pontine neurons and the expression of the α6 GABAA receptor subunit at the mossy fiber-granule cell synapse are perturbed, as well as the innervation of Purkinje cells by cerebellar climbing fibers. Ultrastructural and functional studies revealed a reduced size of mossy fiber boutons, with fewer synaptic vesicles and altered synaptic transmission. These data imply that Piccolo is required for the normal development, maturation, and function of neuronal networks formed between the brainstem and cerebellum. Consistently, behavioral studies demonstrated that adult Pclogt/gt rats display impaired motor coordination, despite adequate performance in tasks that reflect muscle strength and locomotion. Together, these data suggest that loss of Piccolo function in patients with PCH3 could be involved in many of the observed anatomical and behavioral symptoms, and that the further analysis of these animals could provide fundamental mechanistic insights into this devastating disorder.SIGNIFICANCE STATEMENT Pontocerebellar Hypoplasia Type 3 is a devastating developmental disorder associated with severe developmental delay, progressive microcephaly with brachycephaly, optic atrophy, seizures, and hypertonia with hyperreflexia. Recent genetic studies have identified non-sense mutations in the coding region of the PCLO gene, suggesting a functional link between this disorder and the presynaptic active zone. Our analysis of Piccolo KO rats supports this hypothesis, formally demonstrating that anatomical and behavioral phenotypes seen in patients with Pontocerebellar Hypoplasia Type 3 are also exhibited by these Piccolo deficient animals.

Changes in proliferation activity and relative distributions of lymphoid cell subpopulations in congenitally athymic nu/nu mice and Lurcher mice with spontaneous olivopontocerebellar degeneration

Changes observed in mice with congenital damage of some part of the CNS-neuroendocrine-immune regulatory system are described. nu/nu mice with congenital absence of thymus and Lurcher mice with spontaneous olivopontocerebellar degeneration displayed changes in the histoarchitecture of adrenal gland, immune organs (thymus, spleen, axillar lymph nodes) and intestine. Changes were also observed in IgM+, IgG+, CD4+ and CD8+ lymphoid cell subpopulations in the main lymphoid organs--the spleen and axillar lymph nodes and in the proliferative ability of whole lymphoid cell populations. The extreme decrease of lymphoid T-cell subpopulations in athymic nu/nu mice is the consequence of the absence of thymus, the organ of their maturation. On the other hand, a relative increase of B-cell subpopulations was found in this mouse strain. A relative decrease of CD4+ lymphocytes and a different influence of immunization on B-cell subpopulations were found in the spleen in neurodeficient Lurcher mice. The high percentage of apoptotic cells, cells in the S-phase of cell cycle and increased proliferation index in nu/nu mice suggest that the turnover and renewal of lymphoid cells in the spleen in nu/nu mice is more rapid than in control immunocompetent BALB/c mice.

An adult case of adrenoleukodystrophy with features of olivo-ponto-cerebellar atrophy: II. Lipid biochemical studies

Different portions with or without demyelination or degeneration of formalin-fixed brain tissues of a patient with adrenoleukodystrophy and a control subject were applied to analyses of lipids, particularly sphingolipids and cholesteryl ester. Demyelinated area of the white matter in the occipital lobe showed marked decrease in cerebroside and sulfatide except for sphingomyelin and, conversely an accumulation of cholesteryl ester, whereas un-demyelinated white matter in the frontal lobe showed no abnormalities in lipids. Abnormalities of lipids in degenerated lateral nuclei of the thalamus were not so remarkable as the demyelinated white matter, whereas apparently normal dorsomedial nuclei of the thalamus showed no abnormalities in lipids. With regard to the fatty acid composition of abnormal lipids in the demyelinated white matter, all sphingolipids of cerebroside, sulfatide, and sphingomyelin showed remarkable reduction of their longer chain fatty acids and, conversely a significant increment of shorter chain fatty acids. However, these fatty acids in the degenerated lateral nuclei of the thalamus were not so different from those in the undemyelinated and apparently normal areas as well as in control brain. The fatty acids of cholesteryl ester contained mainly C18:1 and C16 acids, and very long chain fatty acids, namely fatty acids with chain length more than 22 carbons, by about 22% of the total fatty acids. In view of the analytical results of the fatty acid composition of brain lipids, it was inconceivable that this ALD patient brain showed especially the accumulation of very long chain fatty acids, and that the biochemical defect in this disease was related to the abnormal oxidation of very long chain fatty acids in peroxisomes. However, the neuropathological findings of demyelination, reactive astrocytosis, and massive infiltration of foam cells well correlated with the abnormalities in myelin lipids and the accumulation of cholesteryl ester. Also, the lower values of urinary 17-ketosteroid and 17-hydroxycorticosteroid suggested that the failure of ACTH to stimulate corticoid secretion seemed to indicate the relationship between the adrenocortical insufficiency and the affected areas of the central nervous system.