O'Sullivan-McLeod syndrome: Unmasking a rare atypical motor neuron disease

A decade of whole-exome sequencing in Brazilian Neurology: from past insights to future perspectives

Over the last decade, whole-exome sequencing (WES) has become a standard diagnostic tool, significantly transforming the landscape of clinical genetics and playing a pivotal role in the diagnosis of neurogenetic diseases. This revolutionary shift has left a lasting impact on the field of neurology in Brazil. The current review article examines key developments and milestones achieved in Brazil through the application of WES in neurology and discusses forthcoming challenges and essential steps to advance molecular diagnosis. Several studies report the use of WES to diagnose genetic disorders with neurological manifestations in Brazil, underscoring the growing importance of molecular diagnosis in neurogenetics. These studies often provide detailed phenotypic analyses and clinical descriptions, offering valuable insights into the genetic underpinnings of several neurological conditions. Many reports highlight the use of WES in the investigation of complex neurological conditions in Brazil, such as neurodevelopmental disorders, hereditary spastic paraplegia, movement disorders, and ataxia. The discovery of new genes implicated in monogenic diseases with neurological manifestations through WES was a significant breakthrough. Despite these advances, the availability of large cohort studies on rare diseases in Brazil remains limited, hindering the ability to generalize findings and explore the full spectrum of genetic diversity. However, a few larger cohort studies have substantially contributed to our understanding of rare diseases and specific neurological disorders.While WES has limitations and may eventually be supplanted by more advanced diagnostic tools, it left a permanent mark on the neurology field in Brazil. The field of neurogenetics is set to become increasingly important in the future.

Sensory Dysfunction in ALS and Other Motor Neuron Diseases: Clinical Relevance, Histopathology, Neurophysiology, and Insights from Neuroimaging

Background: The clinical profiles of MNDs are dominated by inexorable motor decline, but subclinical proprioceptive, nociceptive and somatosensory deficits may also exacerbate mobility, dexterity, and bulbar function. While extra-motor pathology and frontotemporal involvement are widely recognised in motor neuron diseases (MNDs), reports of sensory involvement are conflicting. The potential contribution of sensory deficits to clinical disability is not firmly established and the spectrum of sensory manifestations is poorly characterised. Methods: A systematic review was conducted to examine the clinical, neuroimaging, electrophysiology and neuropathology evidence for sensory dysfunction in MND phenotypes. Results: In ALS, paraesthesia, pain, proprioceptive deficits and taste alterations are sporadically reported and there is also compelling electrophysiological, histological and imaging evidence of sensory network alterations. Gait impairment, impaired dexterity, and poor balance in ALS are likely to be multifactorial, with extrapyramidal, cerebellar, proprioceptive and vestibular deficits at play. Human imaging studies and animal models also confirm dorsal column-medial lemniscus pathway involvement as part of the disease process. Sensory symptoms are relatively common in spinal and bulbar muscular atrophy (SBMA) and Hereditary Spastic Paraplegia (HSP), but are inconsistently reported in primary lateral sclerosis (PLS) and in post-poliomyelitis syndrome (PPS). Conclusions: Establishing the prevalence and nature of sensory dysfunction across the spectrum of MNDs has a dual clinical and academic relevance. From a clinical perspective, subtle sensory deficits are likely to impact the disability profile and care needs of patients with MND. From an academic standpoint, sensory networks may be ideally suited to evaluate propagation patterns and the involvement of subcortical grey matter structures. Our review suggests that sensory dysfunction is an important albeit under-recognised facet of MND.

Cervical lower motor neuron syndromes: A diagnostic challenge

Cervical lower motor neuron (LMN) syndromes, also known as brachial paresis, are characterized by muscle atrophy, weakness, and decreased reflexes in the upper limbs, devoid of sensory symptoms. These syndromes can stem from various factors, including degenerative conditions, immune-mediated diseases, infections, toxic exposures, metabolic disorders, and vascular anomalies.1 Clinical presentations vary, with motor neuron involvement potentially limited to the cervical area or extending to other regions, affecting prognosis. Misdiagnosis is a significant issue, particularly in lower motor neuron presentations, with an error rate nearing 20 %.2 This review proposes a classification system based on magnetic resonance imaging (MRI) findings, the onset timing of symptoms (acute, subacute, or chronic), the symmetry and distribution of atrophy, and the etiology (sporadic or hereditary). Acute conditions may include spinal ischemia,3 whereas subacute or chronic forms can manifest as symmetric (e.g., cervical spondylogenic myelopathy)4 or asymmetric (e.g., Hirayama disease)5 presentations. Neurophysiological assessments and cervical MRI are crucial for accurate diagnosis, as they reveal patterns that provide lesion localization and additional clues to the underlying cause. A systematic diagnostic approach is essential for navigating the complexities of these syndromes.

Amyotrophic Lateral Sclerosis and Other Motor Neuron Diseases

OBJECTIVE

This article reviews the clinical spectrum of amyotrophic lateral sclerosis (ALS), its variant presentations, and the approach to diagnosis and management. This review includes a detailed discussion of current and emerging disease-modifying therapies and the management of respiratory and bulbar manifestations of disease. An updated review of ALS genetics and pathophysiology is also provided. This article also touches on several other important motor neuron diseases.

LATEST DEVELOPMENTS

A new set of simplified diagnostic criteria may help identify patients at earlier stages of the disease. A coformulation of sodium phenylbutyrate and tauroursodeoxycholic acid has been shown to have a significant benefit on disease progression and survival, leading to approval by regulatory authorities in the United States and Canada. An oral formulation of edaravone and an antisense oligonucleotide to a SOD1 gene variation (tofersen) have also recently been approved by the US Food and Drug Administration (FDA). Phase 3 trials of intrathecal mesenchymal stem cells failed to meet primary end points for efficacy. Updated American Academy of Neurology quality measures for the care of patients with ALS were published in 2023.

ESSENTIAL POINTS

There has been continued progress in ALS genetics, diagnosis, and disease-modifying therapies. However, we still lack a definitive biomarker or a treatment that can halt the progression or reverse the course of disease. The evolving understanding of the genetic and pathophysiologic underpinnings of disease offers promise for more effective and clinically meaningful treatments in the future.

Sterol auto-oxidation adversely affects human motor neuron viability and is a neuropathological feature of amyotrophic lateral sclerosis

Aberrant cholesterol homeostasis is implicated in the pathogenesis of amyotrophic lateral sclerosis (ALS), a fatal neuromuscular disease that is due to motor neuron (MN) death. Cellular toxicity from excess cholesterol is averted when it is enzymatically oxidized to oxysterols and bile acids (BAs) to promote its removal. In contrast, the auto oxidation of excess cholesterol is often detrimental to cellular survival. Although oxidized metabolites of cholesterol are altered in the blood and CSF of ALS patients, it is unknown if increased cholesterol oxidation occurs in the SC during ALS, and if exposure to oxidized cholesterol metabolites affects human MN viability. Here, we show that in the SOD1^G93A mouse model of ALS that several oxysterols, BAs and auto oxidized sterols are increased in the lumbar SC, plasma, and feces during disease. Similar changes in cholesterol oxidation were found in the cervical SC of sporadic ALS patients. Notably, auto-oxidized sterols, but not oxysterols and BAs, were toxic to iPSC derived human MNs. Thus, increased cholesterol oxidation is a manifestation of ALS and non-regulated sterol oxidation likely contributes to MN death. Developing therapeutic approaches to restore cholesterol homeostasis in the SC may lead to a treatment for ALS.