Gene/Protein Disease Symptom Drug Enzyme Compound
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Canavan disease (CD) is an inherited leukodystrophy, caused by aspartoacylase (ASPA) deficiency, and accumulation of N-acetylaspartic acid (NAA) in the brain. The gene for ASPA has been cloned and more than 40 mutations have been described, with two founder mutations among Ashkenazi Jewish patients. Screening of Ashkenazi Jews for these two common mutations revealed a high carrier frequency, approximately 1/40, so that programs for carrier testing are currently in practice. The enzyme deficiency in CD interferes with the normal hydrolysis of NAA, which results in disruption of myelin and spongy degeneration of the white matter of the brain. The clinical features of the disease are macrocephaly, head lag, progressive severe mental retardation, and hypotonia in early life, which later changes to spasticity. A knockout mouse for CD has been generated, and used to study the pathophysiological basis for CD. Findings from the knockout mouse indicate that this monogenic trait leads to a series of genomic interaction in the brain. Changes include low levels of glutamate and GABA. Microarray expression analysis showed low level of expression of GABA-A receptor (GABRA6) and glutamate transporter (EAAT4). The gene Spi2, a gene involved in apoptosis and cell death, showed high level of expression. Such complexity of gene interaction results in the phenotype, the proteome, with spongy degeneration of the brain and neurological impairment of the mouse, similar to the human counterpart. Aspartoacylase gene transfer trial in the mouse brain using adenoassociated virus (AAV) as a vector are encouraging showing improved myelination and decrease in spongy degeneration in the area of the injection and also beyond that site.
Mol Genet Metab
PMID:Canavan disease: a monogenic trait with complex genomic interaction. 1456 59

Currently, there are five phase I clinical trials of recombinant adeno-associated viral vectors for the treatment of neurological disorders that are approved or likely to be approved shortly. Two trials are testing different strategies to treat Parkinson's disease (PD), the third trial is aimed at treating Canavan's disease, a pediatric leukodystrophy, the fourth trial targets Alzheimer's disease (AD), and the fifth will attempt to target the lysosomal storage disorder, Batten's disease. All four clinical trials rely on the de novo expression of an enzyme or a trophic factor to correct neuropathology. Ironically, the theories used to choose enzymes for the two PD trials were widely divergent, whereas the enzymatic strategy used for one of the PD trials and the Canavan's trial have remarkable similarities. Other gene therapy treatment strategies for PD and other disorders, such as amyotrophic lateral sclerosis, are also on the horizon.
Curr Opin Mol Ther 2004 Oct
PMID:Clinical trials in neurological disorders using AAV vectors: promises and challenges. 1553 49

Canavan disease is an early onset leukodystrophy associated with psychomotor retardation, seizures, and premature death. This disorder is caused by mutations in the gene encoding the enzyme aspartoacylase (ASPA). Normally, ASPA is enriched in oligodendrocytes and ASPA deficiency results in elevated levels of its substrate molecule, N-acetylaspartate (NAA), brain edema, and dysmyelination. Using adeno-associated virus, we permanently expressed ASPA in CNS neurons of the tremor rat, a genetic model of Canavan disease, and examined the efficacy of the treatment by monitoring NAA metabolism, myelination, motor behavior, and seizures. Assessment of ASPA protein and enzyme activity in whole brain hemispheres showed restoration to normal levels as long as 6 months after treatment. This finding correlated with a reduction of NAA levels, along with a rescue of the seizure phenotype. However, gross brain pathology, such as dilated ventricles and spongiform vacuolization, was unchanged. Moreover, hypomyelination and motor deficits were not resolved by ASPA gene transfer. Our data suggest that NAA-mediated neuronal hyperexcitation but not oligodendrocyte dysfunction can be compensated for by neuronal ASPA expression.
Mol Ther 2005 May
PMID:Restoration of aspartoacylase activity in CNS neurons does not ameliorate motor deficits and demyelination in a model of Canavan disease. 1585 Oct 13

Globoid-cell leukodystrophy (GLD) is an autosomal recessive lysosomal storage disorder caused by mutations in the galactosylceramidase (GALC) gene. Infantile GLD has a lethal course with severe cerebral demyelination that progresses to death by 2 years of age. In the current study twitcher mice, an authentic murine model of infantile GLD, were given intracranial injections of either recombinant adeno-associated virus serotype 2 encoding the murine Galc cDNA (AAV2-GALC) or the same genome pseudotyped with AAV5 capsid proteins (AAV2/5-GALC) on day 3 of age. The group injected intracranially with AAV2/5-GALC had approximately 25-fold greater than normal Galc levels in the brain, while AAV2-GALC-injected animals had 28% normal levels. The average life expectancy of twitcher mice ( approximately 38 days) was significantly (P < 0.0001) increased to 48 and 52 days for the AAV2-GALC- and AAV2/5-GALC-treated groups, respectively. The AAV2/5-GALC group performed significantly better in a battery of behavioral tests compared to untreated, AAV2-GFP-treated, or AAV2-treated twitcher animals. This longitudinal study demonstrated that AAV2/5-GALC-mediated gene therapy resulted in higher levels of Galc expression and slowed the neurologic deterioration more completely than AAV2-GALC in the murine model of globoid-cell leukodystrophy. However, the clinical improvements, as assessed by behavioral tests and life span, were only modest.
Mol Ther 2005 Sep
PMID:AAV2/5 vector expressing galactocerebrosidase ameliorates CNS disease in the murine model of globoid-cell leukodystrophy more efficiently than AAV2. 1599 20

Globoid-cell leukodystrophy (GLD) is a rapidly progressing inherited neurodegenerative disorder caused by a deficiency in galactosylceramidase activity. Previous studies in the murine model of GLD (Twitcher mouse) have shown that both bone marrow transplantation (BMT) and central nervous system (CNS)-directed gene therapy can be moderately effective at ameliorating certain aspects of GLD. As BMT and CNS-directed gene therapy target fundamentally different tissues, we tested the hypothesis that combining these disparate therapies would be more efficacious than either therapy alone. Mice receiving myeloreductive conditioning at birth followed by syngeneic BMT had approximately 25-35% donor chimerism. Untreated Twitcher mice, Twitcher mice treated with BMT alone, AAV2/5 alone, or a combination of BMT and AAV2/5 had mean lifespans of 39, 44, 49, and 104 days, respectively. Twitcher mice treated with a combination of BMT and AAV2/5 also had significantly improved performance in several behavioral tests and greater reduction in demyelination, astrocytosis, and macrophage infiltration compared to untreated Twitcher mice or mice that received either therapy alone. These data suggest that CNS-directed gene therapy synergizes with BMT. The combination of these disparate therapeutic approaches may form the basis for more effective treatment of this inherited neurodegenerative disorder.
Mol Ther 2007 Jan
PMID:Central nervous system-directed AAV2/5-mediated gene therapy synergizes with bone marrow transplantation in the murine model of globoid-cell leukodystrophy. 1716 74

Peripheral demyelinating neuropathy, central dysmyelinating leukodystrophy, Waardenburg syndrome and Hirschsprung disease (PCWH) is a complex neurocristopathy caused by SOX10 mutations. Most PCWH-associated SOX10 mutations result in premature termination codons (PTCs), for which the molecular mechanism has recently been delineated. However, the first mutation reported to cause PCWH was a disruption of the native stop codon that by conceptual translation extends the protein into the 3' untranslated region (3'-UTR) for an additional 82 residues. In this study, we sought to determine the currently unknown molecular pathology for the SOX10 extension mutation using in vitro functional assays. Despite the wild-type SOX10 coding sequence remaining intact, the extension mutation led to severely diminished transcription and DNA-binding activities. Nevertheless, it showed no dominant-negative interference with wild-type SOX10 in vitro. Within the 82-amino acid tail, an 11-amino acid region (termed the WR domain) was responsible primarily for the deleterious properties of the extension. The WR domain, presumably forming an alpha-helix structure, inhibited SOX10 transcription activities if inserted in the carboxyl-terminal half of the protein. The WR domain can also affect other transcription factors with a graded effect when fused to the carboxyl termini, suggesting that it probably elicits a toxic functional activity. Together, molecular pathology for the SOX10 extension mutation is distinct from that of more common PTC mutations. Failure to properly terminate SOX10 translation causes the generation of a deleterious functional domain that occurs because of translation of the normal 3'-UTR; the mutant fusion protein causes a severe neurological disease.
Hum Mol Genet 2007 Dec 15
PMID:Translation of SOX10 3' untranslated region causes a complex severe neurocristopathy by generation of a deleterious functional domain. 1785 51

CLC genes are expressed in species from bacteria to human and encode Cl(-)-channels or Cl(-)/H(+)-exchangers. CLC proteins assemble to dimers, with each monomer containing an ion translocation pathway. Some mammalian isoforms need essential beta -subunits (barttin and Ostm1). Crystal structures of bacterial CLC Cl(-)/H(+)-exchangers, combined with transport analysis of mammalian and bacterial CLCs, yielded surprising insights into their structure and function. The large cytosolic carboxy-termini of eukaryotic CLCs contain CBS domains, which may modulate transport activity. Some of these have been crystallized. Mammals express nine CLC isoforms that differ in tissue distribution and subcellular localization. Some of these are plasma membrane Cl(-) channels, which play important roles in transepithelial transport and in dampening muscle excitability. Other CLC proteins localize mainly to the endosomal-lysosomal system where they may facilitate luminal acidification or regulate luminal chloride concentration. All vesicular CLCs may be Cl(-)/H(+)-exchangers, as shown for the endosomal ClC-4 and -5 proteins. Human diseases and knockout mouse models have yielded important insights into their physiology and pathology. Phenotypes and diseases include myotonia, renal salt wasting, kidney stones, deafness, blindness, male infertility, leukodystrophy, osteopetrosis, lysosomal storage disease and defective endocytosis, demonstrating the broad physiological role of CLC-mediated anion transport.
Crit Rev Biochem Mol Biol
PMID:CLC chloride channels and transporters: from genes to protein structure, pathology and physiology. 1963 40

It has recently been reported that mutations in MPV17 gene may be causative of mtDNA depletion syndrome (MDS). Patients with this alteration presented with severe liver failure, hypoglycemia, growth retardation and neurological symptoms during the first year of life. We report on the clinical, biochemical and molecular findings of a patient presenting with lethal hepatopathy, polyneuropathy, neurological regression and leukodystrophy associated with mutations in MPV17. Mitochondrial respiratory chain activities were low in liver and within reference values in muscle. However, levels of mtDNA were markedly reduced both in muscle and liver. A novel homozygous mutation in MPV17, c.70+5G>A (IVS1+5G>A), was identified. This intronic change causes the full-length cDNA loss, probably due to loss of strength of the splice donor site of exon 1. Western blot analysis, performed in liver homogenates, further corroborates these results as the amount of patient's protein was highly reduced, or almost absent, compared with that of controls. We also identified an additional alternative spliced form in controls and in the patient, due to exon 2 skipping, that has not previously been reported.
Mol Genet Metab 2008 Jun
PMID:Lethal hepatopathy and leukodystrophy caused by a novel mutation in MPV17 gene: description of an alternative MPV17 spliced form. 1832 34

Megalencephalic leukoencephalopathy with subcortical cysts (MLC) is a rare type of leukodystrophy, most often caused by mutations in the MLC1 gene. MLC1 is an oligomeric plasma membrane (PM) protein of unknown function expressed mainly in glial cells and neurons. Most disease-causing missense mutations dramatically reduced the total and PM MLC1 expression levels in Xenopus oocytes and mammalian cells. The impaired expression of the mutants was verified in primary cultures of rat astrocytes, as well as human monocytes, cell types that endogenously express MLC1, demonstrating the relevance of the tissue culture models. Using a combination of biochemical, pharmacological and imaging methods, we also demonstrated that increased endoplasmatic reticulum-associated degradation and endo-lysosomal-associated degradation can contribute to the cell surface expression defect of the mutants. Based on these results, we suggest that MLC1 mutations reduce protein levels in vivo. Since the expression defect of the mutants could be rescued by exposing the mutant-protein expressing cells to low temperature and glycerol, a chemical chaperone, we propose that MLC belongs to the class of conformational diseases. Therefore, we suggest the use of pharmacological strategies that improve MLC1 expression to treat MLC patients.
Hum Mol Genet 2008 Dec 01
PMID:Molecular pathogenesis of megalencephalic leukoencephalopathy with subcortical cysts: mutations in MLC1 cause folding defects. 1875 78

Hurler syndrome, metachromatic leukodystrophy, globoid-cell leukodystrophy (Krabbe's disease) and X-linked adrenoleukodystrophy are inherited diseases of the CNS that can be cured or arrested by allogeneic hematopoietic stem-cell transplantation (HSCT). Despite significant progress in medical procedures and the availability of banked umbilical cord blood, HSCT is still associated with significant risks of graft failure or GVHD that can lead to death. Transplantation of autologous hematopoietic stem cells genetically modified to express the missing protein may circumvent the majority of the problems associated with allogeneic HSCT. Promising in concept, these strategies are now at a stage to be tested in phase I/II clinical trials to assess safety and potential efficacy.
Curr Opin Mol Ther 2008 Oct
PMID:Hematopoietic stem cell gene therapy in Hurler syndrome, globoid cell leukodystrophy, metachromatic leukodystrophy and X-adrenoleukodystrophy. 1883 Sep 23


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