Kinga Szigeti

Mutation of FIG4 causes neurodegeneration in the pale tremor mouse and patients with CMT4J

Membrane-bound phosphoinositides are signalling molecules that have a key role in vesicle trafficking in eukaryotic cells. Proteins that bind specific phosphoinositides mediate interactions between membrane-bounded compartments whose identity is partially encoded by cytoplasmic phospholipid tags. Little is known about the localization and regulation of mammalian phosphatidylinositol-3,5-bisphosphate (PtdIns(3,5)P2), a phospholipid present in small quantities that regulates membrane trafficking in the endosome–lysosome axis in yeast. Here we describe a multi-organ disorder with neuronal degeneration in the central nervous system, peripheral neuronopathy and diluted pigmentation in the ‘pale tremor’ mouse. Positional cloning identified insertion of ETn2β (early transposon 2β) into intron 18 of Fig4 (A530089I17Rik), the homologue of a yeast SAC (suppressor of actin) domain PtdIns(3,5)P2 5-phosphatase located in the vacuolar membrane. The abnormal concentration of PtdIns(3,5)P2 in cultured fibroblasts from pale tremor mice demonstrates the conserved biochemical function of mammalian Fig4. The cytoplasm of fibroblasts from pale tremor mice is filled with large vacuoles that are immunoreactive for LAMP-2 (lysosomal-associated membrane protein 2), consistent with dysfunction of the late endosome–lysosome axis. Neonatal neurodegeneration in sensory and autonomic ganglia is followed by loss of neurons from layers four and five of the cortex, deep cerebellar nuclei and other localized brain regions. The sciatic nerve exhibits reduced numbers of large-diameter myelinated axons, slowed nerve conduction velocity and reduced amplitude of compound muscle action potentials. We identified pathogenic mutations of human FIG4 (KIAA0274) on chromosome 6q21 in four unrelated patients with hereditary motor and sensory neuropathy. This novel form of autosomal recessive Charcot–Marie–Tooth disorder is designated CMT4J.

Practice Parameter: Evaluation of distal symmetric polyneuropathy: Role of autonomic testing, nerve biopsy, and skin biopsy (an evidence-based review) Report of the American Academy of Neurology, American Association of Neuromuscular and Electrodiagnostic Medicine, and American Academy of Physical Medicine and Rehabilitation

Background: Distal symmetric polyneuropathy (DSP) is the most common variety of neuropathy. Since the evaluation of this disorder is not standardized, the available literature was reviewed to provide evidence-based guidelines regarding the role of autonomic testing, nerve biopsy, and skin biopsy for the assessment of polyneuropathy. Methods: A literature review using MEDLINE, EMBASE, and Current Contents was performed to identify the best evidence regarding the evaluation of polyneuropathy published between 1980 and March 2007. Articles were classified according to a four-tiered level of evidence scheme and recommendations were based upon the level of evidence. Results and Recommendations: 1) Autonomic testing should be considered in the evaluation of patients with polyneuropathy to document autonomic nervous system dysfunction (Level B). Such testing should be considered especially for the evaluation of suspected autonomic neuropathy (Level B) and distal small fiber sensory polyneuropathy (SFSN) (Level C). A battery of validated tests is recommended to achieve the highest diagnostic accuracy (Level B). 2) Nerve biopsy is generally accepted as useful in the evaluation of certain neuropathies as in patients with suspected amyloid neuropathy, mononeuropathy multiplex due to vasculitis, or with atypical forms of chronic inflammatory demyelinating polyneuropathy (CIDP). However, the literature is insufficient to provide a recommendation regarding when a nerve biopsy may be useful in the evaluation of DSP (Level U). 3) Skin biopsy is a validated technique for determining intraepidermal nerve fiber density and may be considered for the diagnosis of DSP, particularly SFSN (Level C). There is a need for additional prospective studies to define more exact guidelines for the evaluation of polyneuropathy. AAN = American Academy of Neurology; AANEM = American Academy of Neuromuscular and Electrodiagnostic Medicine; AAPM&R = American Academy of Physical Medicine and Rehabilitation; ART = autonomic reflex testing; BRSI = baroreflex sensitivity index; CASS = composite autonomic scoring scale; CIDP = chronic inflammatory demyelinating polyneuropathy; DSFN = distal small fiber neuropathy; DSP = distal symmetric polyneuropathy; EDx = electrodiagnosis; EFNS = European Federation of Neurological Societies; HRV = heart rate variability; IAN = idiopathic autonomic neuropathy; IENF = intraepidermal nerve fibers; MSNA = muscle sympathetic nerve activity; NCSs = nerve conduction studies; PGP 9.5 = protein-gene-product 9.5; PN = peripheral neuropathy; PRT = blood pressure recovery time; QAE = quantitative autonomic examination; QSART = quantitative sudomotor axon reflex test; QSS = Quality Standards Subcommittee; QST = quantitative sensory testing; SFSN = small fiber sensory polyneuropathy; TST = thermoregulatory sweat testing.

Practice parameter: the evaluation of distal symmetric polyneuropathy: the role of autonomic testing, nerve biopsy, and skin biopsy (an evidence-based review). Report of the American Academy of Neurology, the American Association of Neuromuscular and Electrodiagnostic Medicine, and the American Academy of Physical Medicine and Rehabilitation.

Distal symmetric polyneuropathy (DSP) is the most common variety of neuropathy. Since the evaluation of this disorder is not standardized, the available literature was reviewed to provide evidence‐based guidelines regarding the role of autonomic testing, nerve biopsy and skin biopsy for the assessment of polyneuropathy.

Down-Regulation of p27 Is Associated with Development of Colorectal Adenocarcinoma Metastases

The cyclin-dependent kinase inhibitor p27 is a negative regulator of the cell cycle and a potential tumor suppressor gene. Because we had previously demonstrated that loss of p27 protein is associated with aggressive behavior in colorectal adenocarcinomas, we used immunohistochemistry and in situ hybridization to evaluate the potential role of alterations in p27 expression in primary and metastatic colorectal adenocarcinomas. Parallel immunostaining was performed for Ki-67 and p53. We evaluated 13 cases of metachronous and 23 cases of synchronous primary and metastatic colorectal tumor pairs. In the synchronous subgroup (Stage IV tumors), 57% of the primary tumor and metastases pairs did not express p27 protein and the remainder were low expressors. In the metachronous subgroup, 54% of the primary tumors were low expressors and the remainder high expressors of p27 protein. There was a significant reduction in the expression of p27 in the metachronous metastases (mean positive cells: 14.5%) when compared to the corresponding primary tumors (mean positive cells: 41.8%), P = 0.0023. All the primary and metastatic tumors in the metachronous subgroup showed high levels of p27 mRNA expression. There was no association between loss of p27 and either Ki-67 count or p53 expression. Because p27 is known to be up-regulated when epithelial cells are grown in suspension, the down-regulation of p27 in circulating tumor cells may confer the ability to grow in an environment of altered extracellular matrix or intercellular adhesion properties, two situations which may facilitate metastases.

Practice Parameter: Evaluation of distal symmetric polyneuropathy: Role of laboratory and genetic testing (an evidence-based review) Report of the American Academy of Neurology, American Association of Neuromuscular and Electrodiagnostic Medicine, and American Academy of Physical Medicine and Rehabilitation

Background: Distal symmetric polyneuropathy (DSP) is the most common variety of neuropathy. Since the evaluation of this disorder is not standardized, the available literature was reviewed to provide evidence-based guidelines regarding the role of laboratory and genetic tests for the assessment of DSP. Methods: A literature review using MEDLINE, EMBASE, and Current Contents was performed to identify the best evidence regarding the evaluation of polyneuropathy published between 1980 and March 2007. Articles were classified according to a four-tiered level of evidence scheme and recommendations were based upon the level of evidence. Results and Recommendations: 1) Screening laboratory tests may be considered for all patients with polyneuropathy (Level C). Those tests that provide the highest yield of abnormality are blood glucose, serum B12 with metabolites (methylmalonic acid with or without homocysteine), and serum protein immunofixation electrophoresis (Level C). If there is no definite evidence of diabetes mellitus by routine testing of blood glucose, testing for impaired glucose tolerance may be considered in distal symmetric sensory polyneuropathy (Level C). 2) Genetic testing should be conducted for the accurate diagnosis and classification of hereditary neuropathies (Level A). Genetic testing may be considered in patients with cryptogenic polyneuropathy who exhibit a hereditary neuropathy phenotype (Level C). Initial genetic testing should be guided by the clinical phenotype, inheritance pattern, and electrodiagnostic features and should focus on the most common abnormalities which are CMT1A duplication/HNPP deletion, Cx32 (GJB1), and MFN2 mutation screening. There is insufficient evidence to determine the usefulness of routine genetic testing in patients with cryptogenic polyneuropathy who do not exhibit a hereditary neuropathy phenotype (Level U). AAN = American Academy of Neurology; AANEM = American Academy of Neuromuscular and Electrodiagnostic Medicine; AAPM&R = American Academy of Physical Medicine and Rehabilitation; CMT = Charcot-Marie-Tooth; DSP = distal symmetric polyneuropathy; EDX = electrodiagnostic; GTT = glucose tolerance testing; IFE = immunofixation electrophoresis; QSS = Quality Standards Subcommittee; SPEP = serum protein electrophoresis.

Compound Heterozygosity for Loss-of-Function Lysyl-tRNA Synthetase Mutations in a Patient with Peripheral Neuropathy

Charcot-Marie-Tooth (CMT) disease comprises a genetically and clinically heterogeneous group of peripheral nerve disorders characterized by impaired distal motor and sensory function. Mutations in three genes encoding aminoacyl-tRNA synthetases (ARSs) have been implicated in CMT disease primarily associated with an axonal pathology. ARSs are ubiquitously expressed, essential enzymes responsible for charging tRNA molecules with their cognate amino acids. To further explore the role of ARSs in CMT disease, we performed a large-scale mutation screen of the 37 human ARS genes in a cohort of 355 patients with a phenotype consistent with CMT. Here we describe three variants (p.Leu133His, p.Tyr173SerfsX7, and p.Ile302Met) in the lysyl-tRNA synthetase (KARS) gene in two patients from this cohort. Functional analyses revealed that two of these mutations (p.Leu133His and p.Tyr173SerfsX7) severely affect enzyme activity. Interestingly, both functional variants were found in a single patient with CMT disease and additional neurological and non-neurological sequelae. Based on these data, KARS becomes the fourth ARS gene associated with CMT disease, indicating that this family of enzymes is specifically critical for axon function.

Practice Parameter: The Evaluation of Distal Symmetric Polyneuropathy: The Role ofLaboratory and Genetic Testing (An Evidence-Based Review): Report of the American Academy of Neurology, the American Association of Neuromuscular and Electrodiagnostic Medicine, and the American Academy of Physical Medicine and Rehabilitation

Distal symmetric polyneuropathy (DSP) is the most common variety of neuropathy. Since the evaluation of this disorder is not standardized, the available literature was reviewed to provide evidence‐based guidelines regarding the role of laboratory and genetic tests for the assessment of DSP.

Charcot–Marie–Tooth disease

Charcot-Marie-Tooth (CMT) disease is a heterogeneous group of genetic disorders presenting with the phenotype of a chronic progressive neuropathy affecting both the motor and sensory nerves. During the last decade over two dozen genes have been identified in which mutations cause CMT. The disease illustrates a multitude of genetic principles, including diverse mutational mechanisms from point mutations to copy number variation (CNV), allelic heterogeneity, age-dependent penetrance and variable expressivity. Population based studies have determined the contributions of the various genes to disease burden enabling evidence-based approaches to genetic testing.

Evaluation of distal symmetric polyneuropathy: the role of autonomic testing, nerve biopsy, and skin biopsy (an evidence-based review).

Distal symmetric polyneuropathy (DSP) is the most common variety of neuropathy. Since the evaluation of this disorder is not standardized, the available literature was reviewed to provide evidence‐based guidelines regarding the role of autonomic testing, nerve biopsy, and skin biopsy for the assessment of polyneuropathy. A literature review using MEDLINE, EMBASE, Science Citation Index, and Current Contents was performed to identify the best evidence regarding the evaluation of polyneuropathy published between 1980 and March 2007. Articles were classified according to a four‐tiered level of evidence scheme and recommendations were based on the level of evidence. (1) Autonomic testing may be considered in the evaluation of patients with polyneuropathy to document autonomic nervous system dysfunction (Level B). Such testing should be considered especially for the evaluation of suspected autonomic neuropathy (Level B) and distal small fiber sensory polyneuropathy (SFSN) (Level C). A battery of validated tests is recommended to achieve the highest diagnostic accuracy (Level B). (2) Nerve biopsy is generally accepted as useful in the evaluation of certain neuropathies as in patients with suspected amyloid neuropathy, mononeuropathy multiplex due to vasculitis, or with atypical forms of chronic inflammatory demyelinating polyneuropathy (CIDP). However, the literature is insufficient to provide a recommendation regarding when a nerve biopsy may be useful in the evaluation of DSP (Level U). (3) Skin biopsy is a validated technique for determining intraepidermal nerve fiber (IENF) density and may be considered for the diagnosis of DSP, particularly SFSN (Level C). There is a need for additional prospective studies to define more exact guidelines for the evaluation of polyneuropathy. Muscle Nerve 39: 106–115, 2009

Molecular mechanisms, diagnosis, and rational approaches to management of and therapy for Charcot-Marie-Tooth disease and related peripheral neuropathies

During the last decade, 18 genes and 11 additional loci harboring candidate genes have been associated with Charcot-Marie-Tooth disease (CMT) and related peripheral neuropathies. Ten of these 18 genes have been identified in the last 2 years. This phenomenal pace of CMT gene discovery has fomented an unprecedented explosion of information regarding peripheral nerve biology and its pathologic manifestations in CMT. This review integrates molecular genetics with the clinical phenotypes and provides a flowchart for molecular-based diagnostics. In addition, we discuss rational approaches to molecular therapeutics, including novel biologic molecules (eg, small interfering ribonucleic acid [siRNA], antisense RNA, and ribozymes) that potentially could be used as drugs in the future. These may be applicable in attempts to normalize gene expression in cases of CMT type 1 A, wherein a 1.5 Mb genomic duplication causes an increase in gene dosage that is associated with the majority of CMT cases. Aggresome formation by the PMP22 gene product, the disease-associated gene in the duplication cases, could thus be avoided. We also discuss alternative therapeutics, in light of other neurodegenerative disorders, to disrupt such aggresomes. Finally, we review rational therapeutic approaches, including the use of antioxidants such as vitamin E, coenzyme Q10, or lipoic acid to relax potential oxidative stress in peripheral nerves, for CMT management.