Classification, diagnosis and potential mechanisms in Pontocerebellar Hypoplasia

Pontocerebellar Hypoplasia (PCH) is group of very rare, inherited progressive neurodegenerative disorders with prenatal onset. Up to now seven different subtypes have been reported (PCH1-7). The incidence of each subtype is unknown. All subtypes share common characteristics, including hypoplasia/atrophy of cerebellum and pons, progressive microcephaly, and variable cerebral involvement. Patients have severe cognitive and motor handicaps and seizures are often reported. Treatment is only symptomatic and prognosis is poor, as most patients die during infancy or childhood. The genetic basis of different subtypes has been elucidated, which makes prenatal testing possible in families with mutations. Mutations in three tRNA splicing endonuclease subunit genes were found to be responsible for PCH2, PCH4 and PCH5. Mutations in the nuclear encoded mitochondrial arginyl- tRNA synthetase gene underlie PCH6. The tRNA splicing endonuclease, the mitochondrial arginyl- tRNA synthetase and the vaccinia related kinase1 are mutated in the minority of PCH1 cases. These genes are involved in essential processes in protein synthesis in general and tRNA processing in particular. In this review we describe the neuroradiological, neuropathological, clinical and genetic features of the different PCH subtypes and we report on in vitro and in vivo studies on the tRNA splicing endonuclease and mitochondrial arginyl-tRNA synthetase and discuss their relation to pontocerebellar hypoplasia

Clinical diagnosis, biochemical findings and MRI spectrum of peroxisomal disorders

Peroxisomal disorders are an important group of neurometabolic diseases. The clinical presentation is varied in terms of age of onset severity, and different neurological symptoms. The clinical course spans from death in infancy, rapid functional decline, slow decline on long-term followup, to apparent stable course. Leukoencephalopathy and developmental anomalies are characteristic findings on cerebral MR imaging. From a diagnostic point of view the disorders can be clinically subdivided into four broad categories: (1) the Zellweger spectrum disorders and the peroxisomal beta-oxidation disorders, (2) the rhizomelic chondrodysplasia punctata spectrum disorders, (3) the X-linked adrenoleukodystrophy/adrenomyeloneuropathy complex and (4) the remaining disorders. This article discusses the role of MRI findings in the clinical approach of peroxisomal disorders with neurological disease. This article is part of a Special Issue entitled: Metabolic Functions and Biogenesis of peroxisomes in Health and Disease. (C) 2012 Elsevier B.V. All rights reserve

Peroxisomal Leukoencephalopathy

Peroxisomal leukoencephalopathies include diseases belonging to the Zellweger spectrum and the rhizomelic chondrodysplasia punctata spectrum, as well as some single enzyme defects of peroxisomal beta-oxidation. The authors present information on the clinical and diagnostic approach, and the characteristics of brain magnetic resonance imaging (MRI) in these diseases. MRIs of patients belonging to the Zellweger spectrum may show developmental anomalies and regressive changes consisting of abnormal cerebral white matter. Involvement of the central white matter of the cerebellar hemispheres is frequently seen. The leukoencephalopathy is progressive, with or without peripheral nerve involvement, in patients with a prolonged course of the disease. MRI characteristics in the severe phenotype of rhizomelic chondrodysplasia punctata include supratentorial white matter abnormalities, with a parietooccipital predominance. Demyelinative lesions are the hallmark of the cerebral form of X-linked adrenoleukodystrophy and may appear in a similar way in patients with adrenomyeloneuropathy progressing to a cerebral form. The diagnosis of a peroxisomal disorder can be determined by a battery of biochemical assays in blood and/or urine, and should be confirmed in cultured fibroblasts and DNA analysis. Treatment of the peroxisomal leukoencephalopathies is largely symptomatic, except for boys affected by the cerebral form of X-linked adrenoleukodystrophy in whom a bone marrow/hematopoietic stem cell transplant can be lifesaving, at least in the early stages of the diseas

"Role of peroxisomes in human lipid metabolism and its importance for neurological development"

Peroxisomes play a crucial role in normal neurological development as exemplified by the devastating neurological consequences of a defect in the biogenesis of peroxisomes as in Zellweger syndrome. The underlying basis for the important role of peroxisomes in neurological development resides in the fact that peroxisomes catalyze a number of physiological functions, notably involving the metabolism of different lipids. Indeed, peroxisomes catalyse the beta-oxidative breakdown of certain fatty acids including: (1.) the very long-chain fatty acids C22:0, C24:0, and C26:0; (2.) pristanic acid and (3.) the bile acid intermediates di- and trihydroxycholestanoic acid which cannot be oxidized in mitochondria. Furthermore, peroxisomes catalyze the synthesis of a particular type of lipids, i.e. ether-linked phospholipids, which are highly abundant in brain, especially in myelin. The current state of knowledge with respect to the metabolic role of peroxisomes will be described in this paper with particular emphasis on the role of peroxisomes in brai

X-linked adrenoleukodystrophy: pathogenesis and treatment

X-linked adrenoleukodystrophy (X-ALD) is a puzzling inborn error of metabolism with a strikingly heterogeneous clinical spectrum. All patients have mutations in the ABCD1 gene and accumulate very long chain fatty acids in all tissues. Virtually all male X-ALD patients develop adrenocortical insufficiency in childhood and progressive myelopathy and peripheral neuropathy in adulthood. A subset of male patients, however, develops a fatal cerebral demyelinating disease, cerebral adrenoleukodystrophy. Female patients also develop progressive myelopathy and peripheral neuropathy, but generally at a later age than males. They only very rarely develop adrenocortical insufficiency or cerebral adrenoleukodystrophy. This review proposes to simplify the classification of the clinical spectrum of X-ALD and reviews the largely unresolved pathophysiological mechanisms and the current treatment option