Animal models of leukodystrophy: a new perspective for the development of therapies.

The leukodystrophies are a family of heritable disorders characterised by white matter degeneration, accompanied by variable clinical symptoms including loss of motor function and cognitive decline. Now thought to include over 50 distinct disorders, there are a vast array of mechanisms underlying the pathology of these monogenic conditions and, accordingly, a range of animal models relating to each disorder. While both murine and zebrafish models continue to aid in the development of potential therapies, many of these models fail to truly recapitulate the human condition - thus leaving substantial weaknesses in our understanding of leukodystrophy pathogenesis. Additionally, the heterogeneity in leukodystrophy presentation - both in patients and in vivo models - often results in a narrow focus on single disorders in isolation across much of the literature. Thus, this review aims to synthesise prominent research regarding the most common leukodystrophies in order to provide an overview of key animal models and their utility in developing novel treatments. We begin by discussing the ongoing revolution across the leukodystrophy field following the rise of next generation sequencing, before focusing more extensively on existing animal models from the mouse and zebrafish fields. Finally, we explore how these preclinical models have shaped the development of therapeutic strategies currently in development. We propose future directions for the field and suggest a more critical view of the dogma which has underpinned leukodystrophy research for decades.

Respiratory difficulty with palatal, laryngeal and respiratory muscle tremor in adult-onset Alexander's disease.

Sleep apnoea and respiratory difficulties are reported in adult-onset Alexander's disease (AOAD), an autosomal-dominant leukodystrophy that presents mainly with progressive ataxia. We demonstrate for the first time that the respiratory symptoms can result from association of palatal tremor with a similar tremor of laryngeal and respiratory muscles that interrupts normal inspiration and expiration.A 60-year-old woman presented with progressive ataxia, palatal tremor and breathlessness. MRI revealed medullary atrophy, bilateral T2 hyperintensities in the dentate nuclei and hypertrophic olivary degeneration (HOD). AOAD was confirmed genetically with a positive glial fibrillary acidic protein (GFAP) mutation. Electrophysiological study revealed 1.5 Hz rhythmic laryngeal and respiratory muscle activity. Her respiratory symptoms were significantly improved at night with variable positive pressure ventilation.This case illustrates that palatal tremor in AOAD, and potentially in other conditions, may be associated with treatable breathlessness due to a similar tremor of respiratory muscles.

Astrocyte Dysfunction in Developmental Neurometabolic Diseases.

Astrocytes play crucial roles in maintaining brain homeostasis and in orchestrating neural development, all through tightly coordinated steps that cooperate to maintain the balance needed for normal development. Here, we review the alterations in astrocyte functions that contribute to a variety of developmental neurometabolic disorders and provide additional data on the predominant role of astrocyte dysfunction in the neurometabolic neurodegenerative disease glutaric acidemia type I. Finally, we describe some of the therapeutical approaches directed to neurometabolic diseases and discuss if astrocytes can be possible therapeutic targets for treating these disorders.

Alexander's disease: reassessment of a neonatal form.

INTRODUCTION: Alexander disease is a disorder caused by a mutation and accumulation of the glial fibrillary acidic protein. Currently, three subtypes are acknowledged: an infantile, a juvenile, and an adult form. However, onset early in infancy or in the prenatal period has been shown to present with a uniform pattern of symptoms-suggesting the presence of a distinct neonatal form of the disease. RESULTS AND DISCUSSION: Though the neonatal form of Alexander disease is not well acknowledged, a uniform and distinct presentation of the disease in neonates has been observed, suggesting the need for a different course of identification and treatment. Clinical presentation of the neonatal form is distinguished by leukodystrophy and generalized, frequent, and intractable seizures. While the infantile form presents with ataxia, hyperreflexia, and other upper motor neuron symptoms, none of these has been observed in the neonatal form. In the diagnosis of neonatal Alexander disease, it is essential to rule out other causes of leukodystrophy and the presence of neoplasms.

Strategies for treatment in Alexander disease.

Alexander disease is a rare and generally fatal disorder of the CNS, originally classified among the leukodystrophies because of the prominent myelin deficits found in young patients. The most common form of this disease affects infants, who often have profound mental retardation and a variety of developmental delays, but later onset forms also occur, sometimes with little or no white matter pathology at all. The pathological hallmark of Alexander disease is the inclusion body, known as Rosenthal fiber, within the cell bodies and processes of astrocytes. Recent genetic studies identified heterozygous missense mutations in glial fibrillary acidic protein (GFAP), the major intermediate filament protein in astrocytes, as the cause of nearly all cases of Alexander disease. These studies have transformed our view of this disorder and opened new directions for investigation and clinical practice, particularly with respect to diagnosis. Mechanisms by which expression of mutant forms of glial fibrillary acidic protein (GFAP) lead to the pleiotropic manifestations of disease (afflicting cell types beyond the ones expressing the mutant gene) are slowly coming into focus. Ideas are beginning to emerge that suggest several compelling therapeutic targets for interventions that might slow or arrest the evolution of the disease. This review will outline the rationale for pursuing these strategies, and highlight some of the critical issues that must be addressed in the planning of future clinical trials.