Characterization of the cystatin B gene promoter harboring the dodecamer repeat expanded in progressive myoclonus epilepsy, EPM1

The Roles of Cystatin B in the Brain and Pathophysiological Mechanisms of Progressive Myoclonic Epilepsy Type 1

Progressive myoclonic epilepsy type 1 (EPM1) is an autosomal recessive disorder, also known as Unverricht-Lundborg disease (ULD). EPM1 patients suffer from photo-sensitive seizures, stimulus-sensitive myoclonus, nocturnal myoclonic seizures, ataxia and dysarthria. In addition, cerebral ataxia and impaired GABAergic inhibition are typically present. EPM1 is caused by mutations in the Cystatin B gene (CSTB). The CSTB protein functions as an intracellular thiol protease inhibitor and inhibits Cathepsin function. It also plays a crucial role in brain development and regulates various functions in neurons beyond maintaining cellular proteostasis. These include controlling cell proliferation and differentiation, synaptic functions and protection against oxidative stress, likely through regulation of mitochondrial function. Depending on the differentiation stage and status of neurons, the protein localizes either to the cytoplasm, nucleus, lysosomes or mitochondria. Further, CSTB can also be secreted to the extracellular matrix for interneuron rearrangement and migration. In this review, we will review the various functions of CSTB in the brain and discuss the putative pathophysiological mechanism underlying EPM1.

Rodent Models of Audiogenic Epilepsy: Genetic Aspects, Advantages, Current Problems and Perspectives

Animal models of epilepsy are of great importance in epileptology. They are used to study the mechanisms of epileptogenesis, and search for new genes and regulatory pathways involved in the development of epilepsy as well as screening new antiepileptic drugs. Today, many methods of modeling epilepsy in animals are used, including electroconvulsive, pharmacological in intact animals, and genetic, with the predisposition for spontaneous or refractory epileptic seizures. Due to the simplicity of manipulation and universality, genetic models of audiogenic epilepsy in rodents stand out among this diversity. We tried to combine data on the genetics of audiogenic epilepsy in rodents, the relevance of various models of audiogenic epilepsy to certain epileptic syndromes in humans, and the advantages of using of rodent strains predisposed to audiogenic epilepsy in current epileptology.

Insights into the Genetic Profile of Two Siblings Affected by Unverricht-Lundborg Disease Using Patient-Derived hiPSCs

Unverricht-Lundborg disease (ULD), also known as progressive myoclonic epilepsy 1 (EPM1), is a rare autosomal recessive neurodegenerative disorder characterized by a complex symptomatology that includes action- and stimulus-sensitive myoclonus and tonic-clonic seizures. The main cause of the onset and development of ULD is a repeat expansion of a dodecamer sequence localized in the promoter region of the gene encoding cystatin B (CSTB), an inhibitor of lysosomal proteases. Although this is the predominant mutation found in most patients, the physio-pathological mechanisms underlying the disease complexity remain largely unknown. In this work, we used patient-specific iPSCs and their neuronal derivatives to gain insight into the molecular and genetic machinery responsible for the disease in two Italian siblings affected by different phenotypes of ULD. Specifically, fragment length analysis on amplified CSTB promoters found homozygous status for dodecamer expansion in both patients and showed that the number of dodecamer repeats is the same in both. Furthermore, the luciferase reporter assay showed that the CSTB promoter activity was similarly reduced in both lines compared to the control. This information allowed us to draw important conclusions: (1) the phenotypic differences of the patients do not seem to be strictly dependent on the genetic mutation around the CSTB gene, and (2) that some other molecular mechanisms, not yet clearly identified, might be taken into account. In line with the inhibitory role of cystatin B on cathepsins, molecular investigations performed on iPSCs-derived neurons showed an increased expression of lysosomal cathepsins (B, D, and L) and a reduced expression of CSTB protein. Intriguingly, the increase in cathepsin expression does not appear to be correlated with the residual amount of CSTB, suggesting that other mechanisms, in addition to the regulation of cathepsins, could be involved in the pathological complexity of the disease.

Length Polymorphism and Methylation Status of UPS29 Minisatellite of the ACAP3 Gene as Molecular Biomarker of Epilepsy. Sex Differences in Seizure Types and Symptoms

Epilepsy is a neurological disease with different clinical forms and inter-individuals heterogeneity, which may be associated with genetic and/or epigenetic polymorphisms of tandem-repeated noncoding DNA. These polymorphisms may serve as predictive biomarkers of various forms of epilepsy. ACAP3 is the protein regulating morphogenesis of neurons and neuronal migration and is an integral component of important signaling pathways. This study aimed to carry out an association analysis of the length polymorphism and DNA methylation of the UPS29 minisatellite of the ACAP3 gene in patients with epilepsy. We revealed an association of short UPS29 alleles with increased risk of development of symptomatic and cryptogenic epilepsy in women, and also with cerebrovascular pathologies, structural changes in the brain, neurological status, and the clinical pattern of seizures in both women and men. The increase of frequency of hypomethylated UPS29 alleles in men with symptomatic epilepsy, and in women with both symptomatic and cryptogenic epilepsy was observed. For patients with hypomethylated UPS29 alleles, we also observed structural changes in the brain, neurological status, and the clinical pattern of seizures. These associations had sex-specific nature similar to a genetic association. In contrast with length polymorphism epigenetic changes affected predominantly the long UPS29 allele. We suppose that genetic and epigenetic alterations UPS29 can modify ACAP3 expression and thereby affect the development and clinical course of epilepsy.

DNA Hypermethylation and Unstable Repeat Diseases: A Paradigm of Transcriptional Silencing to Decipher the Basis of Pathogenic Mechanisms

Unstable repeat disorders comprise a variable group of incurable human neurological and neuromuscular diseases caused by an increase in the copy number of tandem repeats located in various regions of their resident genes. It has become clear that dense DNA methylation in hyperexpanded non-coding repeats induces transcriptional silencing and, subsequently, insufficient protein synthesis. However, the ramifications of this paradigm reveal a far more profound role in disease pathogenesis. This review will summarize the significant progress made in a subset of non-coding repeat diseases demonstrating the role of dense landscapes of 5-methylcytosine (5mC) as a common disease modifier. However, the emerging findings suggest context-dependent models of 5mC-mediated silencing with distinct effects of excessive DNA methylation. An in-depth understanding of the molecular mechanisms underlying this peculiar group of human diseases constitutes a prerequisite that could help to discover novel pathogenic repeat loci, as well as to determine potential therapeutic targets. In this regard, we report on a brief description of advanced strategies in DNA methylation profiling for the identification of unstable Guanine-Cytosine (GC)-rich regions and on promising examples of molecular targeted therapies for Fragile X disease (FXS) and Friedrich ataxia (FRDA) that could pave the way for the application of this technique in other hypermethylated expansion disorders.

Neuropathology and Cellular Pathogenesis of Spinocerebellar Ataxia Type 12

OBJECTIVE

SCA12 is a progressive autosomal-dominant disorder, caused by a CAG/CTG repeat expansion in PPP2R2B on chromosome 5q32, and characterized by tremor, gait ataxia, hyperreflexia, dysmetria, abnormal eye movements, anxiety, depression, and sometimes cognitive impairment. Neuroimaging has demonstrated cerebellar and cortical atrophy. We now present the neuropathology of the first autopsied SCA12 brain and utilize cell models to characterize potential mechanisms of SCA12 neurodegeneration.

METHODS

A fixed SCA12 brain was examined using gross, microscopic, and immunohistochemical methods. The effect of the repeat expansion on PPP2R2B Bβ1 expression was examined in multiple cell types by transient transfection of constructs containing the PPP2R2B Bβ1 promoter region attached to a luciferase reporter. The neurotoxic effect of PPP2R2B overexpression was examined in transfected rat primary neurons.

RESULTS

Neuropathological investigation revealed enlarged ventricles, marked cerebral cortical atrophy and Purkinje cell loss, less-prominent cerebellar and pontine atrophy, and neuronal intranuclear ubiquitin-positive inclusions, consistent with Marinesco bodies, which did not stain for long polyglutamine tracts, alpha-synuclein, tau, or transactive response DNA-binding protein 43. Reporter assays demonstrated that the region of PPP2R2B containing the repeat functions as a promoter, and that promoter activity increases with longer repeat length and is dependent on cell type, repeat sequence, and sequence flanking the repeat. Overexpression of PPP2R2B in primary cortical neurons disrupted normal morphology.

CONCLUSIONS

SCA12 involves extensive, but selective, neurodegeneration distinct from Alzheimer's disease, synucleinopathies, tauopathies, and glutamine expansion diseases. SCA12 neuropathology may arise from the neurotoxic effect of repeat-expansion-induced overexpression of PPP2R2B.

Cystatin B and SOD1: protein–protein interaction and possible relation to neurodegeneration

Cystatin B (CSTB), an inhibitor of the cysteine proteases, belongs to the cathepsin family and it is known to interact with a number of proteins involved in cytoskeletal organization. CSTB has an intrinsic tendency to form aggregates depending on the redox environment. The gene encoding for CSTB is frequently mutated in association with the rare neurodegenerative condition progressive myoclonus epilepsy. Increased levels of CSTB have been observed in the spinal cord of transgenic mice modeling SOD1-linked familial amyotrophic lateral sclerosis, a fatal neurodegenerative disease affecting motoneurons. In the present study, we have investigated the relationship occurring between the expression of SOD1 and CSTB either wild-type or double-cysteine substitution mutant (Cys 3 and Cys 64). Whether or not there is a physical interaction between the two proteins was also investigated in overexpression experiments using a human neuroblastoma cell line and mouse-immortalized motoneurons. Here we report evidences for a reciprocal influence of CSTB and SOD1 at the gene expression level and for a direct interaction of the two proteins.

Tandem repeat sequence variation as causative cis-eQTLs for protein-coding gene expression variation: the case of CSTB

Association studies have revealed expression quantitative trait loci (eQTLs) for a large number of genes. However, the causative variants that regulate gene expression levels are generally unknown. We hypothesized that copy-number variation of sequence repeats contribute to the expression variation of some genes. Our laboratory has previously identified that the rare expansion of a repeat c.-174CGGGGCGGGGCG in the promoter region of the CSTB gene causes a silencing of the gene, resulting in progressive myoclonus epilepsy. Here, we genotyped the repeat length and quantified CSTB expression by quantitative real-time polymerase chain reaction in 173 lymphoblastoid cell lines (LCLs) and fibroblast samples from the GenCord collection. The majority of alleles contain either two or three copies of this repeat. Independent analysis revealed that the c.-174CGGGGCGGGGCG repeat length is strongly associated with CSTB expression (P = 3.14 × 10(-11)) in LCLs only. Examination of both genotyped and imputed single-nucleotide polymorphisms (SNPs) within 2 Mb of CSTB revealed that the dodecamer repeat represents the strongest cis-eQTL for CSTB in LCLs. We conclude that the common two or three copy variation is likely the causative cis-eQTL for CSTB expression variation. More broadly, we propose that polymorphic tandem repeats may represent the causative variation of a fraction of cis-eQTLs in the genome.

A natural antisense transcript at the Huntington's disease repeat locus regulates HTT expression

Huntington's disease (HD) is a progressive neurodegenerative disorder caused by a CAG repeat expansion in exon 1 of huntingtin (HTT). Relatively little attention has been directed to the genomic features of the antisense strand at the HD locus, though the presence of a transcript from this strand has been suggested by a survey of the entire transcriptome and the existence of several EST tags. In this study, we identified huntingtin antisense (HTTAS), a natural antisense transcript at the HD repeat locus that contain the repeat tract. HTTAS is 5' capped, poly (A) tailed and contains three exons, alternatively spliced into HTTAS_v1 (exons 1 and 3) and HTTAS_v2 (exons 2 and 3). Exon 1 includes the repeat. HTTAS_v1 has a weak promoter, and is expressed at low levels in multiple tissue types and throughout the brain. Reporter assays indicate that while efficient promoter activity requires a short repeat, repeat expansion reduces promoter efficiency. Consistent with the reporter assays, levels of HTTAS_v1 are reduced in human HD frontal cortex. In cell systems, overexpression of HTTAS_v1 specifically reduces endogenous HTT transcript levels, while siRNA knockdown of HTTAS_v1 increases HTT transcript levels. Minigene constructs of the HD locus confirm the regulatory effect of HTTAS_v1 on HTT, and demonstrate that the effect is dependent on repeat length and is at least partially Dicer dependent. Together, these findings provide strong evidence for the existence of a gene antisense to HTT, with properties that include regulation of HTT expression.

Mutations in prickle orthologs cause seizures in flies, mice, and humans

Epilepsy is heritable, yet few causative gene mutations have been identified, and thus far no human epilepsy gene mutations have been found to produce seizures in invertebrates. Here we show that mutations in prickle genes are associated with seizures in humans, mice, and flies. We identified human epilepsy patients with heterozygous mutations in either PRICKLE1 or PRICKLE2. In overexpression assays in zebrafish, prickle mutations resulted in aberrant prickle function. A seizure phenotype was present in the Prickle1-null mutant mouse, two Prickle1 point mutant (missense and nonsense) mice, and a Prickle2-null mutant mouse. Drosophila with prickle mutations displayed seizures that were responsive to anti-epileptic medication, and homozygous mutant embryos showed neuronal defects. These results suggest that prickle mutations have caused seizures throughout evolution.

Cystatin B deficiency sensitizes neurons to oxidative stress in progressive myoclonus epilepsy, EPM1

The progressive myoclonus epilepsies, featuring the triad of myoclonus, seizures, and ataxia, comprise a large group of inherited neurodegenerative diseases that remain poorly understood and refractory to treatment. The Cystatin B gene is mutated in one of the most common forms of progressive myoclonus epilepsy, Unverricht-Lundborg disease (EPM1). Cystatin B knockout in a mouse model of EPM1 triggers progressive degeneration of cerebellar granule neurons. Here, we report impaired redox homeostasis as a key mechanism by which Cystatin B deficiency triggers neurodegeneration. Oxidative stress induces the expression of Cystatin B in cerebellar granule neurons, and EPM1 patient-linked mutation of the Cystatin B gene promoter impairs oxidative stress induction of Cystatin B transcription. Importantly, Cystatin B knockout or knockdown sensitizes cerebellar granule neurons to oxidative stress-induced cell death. The Cystatin B deficiency-induced predisposition to oxidative stress in neurons is mediated by the lysosomal protease Cathepsin B. We uncover evidence of oxidative damage, reflected by depletion of antioxidants and increased lipid peroxidation, in the cerebellum of Cystatin B knock-out mice in vivo. Collectively, our findings define a pathophysiological mechanism in EPM1, whereby Cystatin B deficiency couples oxidative stress to neuronal death and degeneration, and may thus provide the basis for novel treatment approaches for the progressive myoclonus epilepsies.

The biological effects of simple tandem repeats: lessons from the repeat expansion diseases

Tandem repeats are common features of both prokaryote and eukaryote genomes, where they can be found not only in intergenic regions but also in both the noncoding and coding regions of a variety of different genes. The repeat expansion diseases are a group of human genetic disorders caused by long and highly polymorphic tandem repeats. These disorders provide many examples of the effects that such repeats can have on many biological processes. While repeats in the coding sequence can result in the generation of toxic or malfunctioning proteins, noncoding repeats can also have significant effects including the generation of chromosome fragility, the silencing of the genes in which they are located, the modulation of transcription and translation, and the sequestering of proteins involved in processes such as splicing and cell architecture.

Molecular background of EPM1-Unverricht-Lundborg disease

Unverricht-Lundborg disease (EPM1) is an autosomal recessively inherited neurodegenerative disorder and the most common single cause of progressive myoclonus epilepsy worldwide. Mutations in the gene encoding cystatin B (CSTB), a cysteine protease inhibitor, are responsible for the primary defect underlying EPM1. Here, progress toward understanding the molecular mechanisms in EPM1 is reviewed. We summarize the current knowledge about the CSTB gene and mutations as well as the cellular biology of the CSTB protein with emphasis on data emerging from analysis of EPM1 patients. We shed light on the disease mechanisms of EPM1 based on characterization of the CSTB-deficient mouse model.

Cystatin B: mutation detection, alternative splicing and expression in progressive myclonus epilepsy of Unverricht-Lundborg type (EPM1) patients

Progressive myoclonus epilepsy of Unverricht-Lundborg type (EPM1) is an autosomal recessive neurodegenerative disorder caused by mutations in the cystatin B gene (CSTB) that encodes an inhibitor of several lysosomal cathepsins. An unstable expansion of a dodecamer repeat in the CSTB promoter accounts for the majority of EPM1 disease alleles worldwide. We here describe a novel PCR protocol for detection of the dodecamer repeat expansion. We describe two novel EPM1-associated mutations, c.149G > A leading to the p.G50E missense change and an intronic 18-bp deletion (c.168+1_18del), which affects splicing of CSTB. The p.G50E mutation that affects the conserved QVVAG amino acid sequence critical for cathepsin binding fails to associate with lysosomes. This further supports the previously implicated physiological importance of the CSTB-lysosome association. Expression of CSTB mRNA and protein was markedly reduced in lymphoblastoid cells of the patients irrespective of the mutation type. Patients homozygous for the dodecamer expansion mutation showed 5-10% expression compared to controls. By combining database searches with RT-PCR we identified several alternatively spliced CSTB isoforms. One of these, CSTB2, was also present in mouse and was analyzed in more detail. In real-time PCR quantification, CSTB2 expression was less than 5% of total CSTB expression in all human adult and fetal tissues analyzed. In patients homozygous for the minisatellite mutation, the level of CSTB2 was reduced similarly to that of CSTB implicating regulation from the same promoter. The physiological significance of CSTB2 remains to be determined.

Assessing radiation-associated mutational risk to the germline: repetitive DNA sequences as mutational targets and biomarkers

This review assesses recent data on mutational risk to the germline after radiation exposure obtained by molecular analysis of tandemly repeated DNA loci (TRDLs): minisatellites in humans and expanded simple tandem repeats in mice. Some studies, particularly those including exposure to internal emitters, indicate that TRDL mutation can be used as a marker of human radiation exposure; most human studies, however, are negative. Although mouse studies have suggested that TRDL mutation analysis may be more widely applicable in biomonitoring, there are important differences between the structure of mouse and human TRDLs. Mutational mechanisms probably differ between the two species, and so care should be taken in predicting effects in humans from mouse data. In mice and humans, TRDL mutations are largely untargeted with only limited evidence of dose dependence. Transgenerational mutation has been observed in mice but not in humans, but the mechanisms driving such mutation transmission are unknown. Some minisatellite variants are associated with human diseases and may affect gene transcription, but causal relationships have not yet been established. It is concluded that at present the TRDL mutation data do not warrant a dramatic revision of germline or cancer risk estimates for radiation.

Loss of lysosomal association of cystatin B proteins representing progressive myoclonus epilepsy, EPM1, mutations

Loss-of-function mutations in the cystatin B (CSTB), a cysteine protease inhibitor, gene underlie progressive myoclonus epilepsy of Unverricht-Lundborg type (EPM1), characterized by myoclonic and tonic-clonic seizures, ataxia and a progressive course. A minisatellite repeat expansion in the promoter region of the CSTB gene is the most common mutation in EPM1 patients and leads to reduced mRNA levels. Seven other mutations altering the structure of CSTB, or predicting altered splicing, have been described. Using a novel monoclonal CSTB antibody and organelle-specific markers in human primary myoblasts, we show here that endogenous CSTB localizes not only to the nucleus and cytoplasm but also associates with lysosomes. Upon differentiation to myotubes, CSTB becomes excluded from the nucleus and lysosomes, suggesting that the subcellular distribution of CSTB is dependent on the differentiation status of the cell. Four patient mutations altering the CSTB polypeptide were transiently expressed in BHK-21 cells. The p.Lys73fsX2-truncated mutant protein shows diffuse cytoplasmic and nuclear distribution, whereas p.Arg68X is rapidly degraded. Two missense mutations, the previously described p.Gly4Arg affecting the highly conserved glycine, critical for cathepsin binding, and a novel mutation, p.Gln71Pro, fail to associate with lysosomes. These data imply an important lysosome-associated physiological function for CSTB and suggest that loss of this association contributes to the molecular pathogenesis of EPM1.

DNA deamination enables direct PCR amplification of the cystatin B (CSTB) gene-associated dodecamer repeat expansion in myoclonus epilepsy type Unverricht-Lundborg

The Unverricht-Lundborg type of progressive myoclonus epilepsy (EPM1) is an autosomal recessive disorder that is caused by the dysfunction of the cystatin B (CSTB) gene product. In the vast majority of affected cases, mRNA transcription is impaired by a biallelic expansion of a dodecamer repeat within the 5'-untranslated region of the respective gene. Since this minisatellite contains exclusively G and C nucleotides, direct PCR analysis of allele expansion is extremely difficult and error prone. To circumvent these problems, we have developed a PCR assay that is based on the deamination of the DNA prior to amplification. We have developed a method based on PCR after DNA deamination of the GC-rich repeat region, which improves the PCR condition to such an extent that we were not only able to reliably amplify expanded alleles of affected individuals (homozygotes and compound heterozygotes), but also the two alleles of full mutation carriers, whose analysis is particularly difficult because of PCR bias and heteroduplex formation between the two alleles. We used promoter- and repeat-specific primer combinations to investigate whether dodecamer repeat expansion concurs with de novo methylation of the CSTB gene promoter in a similar fashion to other repeat expansion syndromes. We confirmed previous evidence obtained by HpaII digestion and Southern blot analysis that both the promoter and the repeat regions are unmethylated, in both healthy and affected individuals. Thus, in contrast to certain trinucleotide repeat expansion-associated diseases, such as fragile X syndrome (FRAXA) and myotonic dystrophy, methylation analyses can not be utilized for indirect diagnostic testing.

The epilepsy, the protease inhibitor and the dodecamer: progressive myoclonus epilepsy, cystatin b and a 12-mer repeat expansion

Progressive myoclonus epilepsy 1 (EPM1) or Unverricht-Lundborg disease is a human autosomal recessive neurodegenerative disorder caused by mutations in cystatin B (CSTB). The CSTB gene maps to human chromosome 21 and encodes an inhibitor of lysosomal cysteine proteases. Five point mutations have been found, two of which are seen in numerous unrelated patients. However, the main CSTB mutation in EPM1, even among patients of different ethnic origins, is an expansion of a dodecamer repeat (CCCCGCCCCGCG) in the 5' flanking area of CSTB. Most normal alleles contain either two or three repeats, while rarer normal alleles that are highly unstable contain between 12 and 17 repeats. Mutant expanded alleles have been reported to contain between 30 and 80 copies and are also highly unstable, particularly via parental transmission. There is no apparent correlation between mutant repeat length and disease phenotype. While the repeat expansion is outside the CSTB transcriptional unit, it results in a marked decrease in CSTB expression, at least in certain cell types in vitro. CSTB homozygous knockout mice show some parallels to the phenotype of human EPM1 including myoclonic seizures, development of ataxia and neuropathological changes associated with cell loss via apoptosis. Loss of CSTB function due to mutations is consistent with the observed neurodegenerative pathology and phenotype, but the functional link to the epileptic phenotype of EPM1 remains largely unknown.

Transcription defects induced by repeat expansion: fragile X syndrome, FRAXE mental retardation, progressive myoclonus epilepsy type 1, and Friedreich ataxia

Fragile X mental retardation syndrome, FRAXE mental retardation, Progressive myoclonus epilepsy Type I, and Friedreich ataxia are members of a larger group of genetic disorders known as the Repeat Expansion Diseases. Unlike other members of this group, these four disorders all result from a primary defect in the initiation or elongation of transcription. In this review, we discuss current models for the relationship between the expanded repeat and the disease symptoms.

Cystatin-B is expressed by neural stem cells and by differentiated neurons and astrocytes

Mutation in the gene encoding cystatin-B (CSTB) has been shown to cause progressive myoclonus epilepsy. Mice with a gene deletion of CSTB exhibit increased apoptosis of specific neurons but the physiological role of CSTB in brain cells is not fully understood. In the present study, we have examined the expression of CSTB in neural stem cells (NSC) and in differentiating mature brain cells. The results show that CSTB is present in embryonic and adult NSC and in the neuroepithelium. CSTB was expressed by both neurons and glial cells differentiated from NSC and in hippocampal cultures. CSTB localized mainly to the nucleus in NSC and in neurons, whilst in astrocytes CSTB was also in the cytoplasm. Double labeling showed that CSTB was present in the lysosomes in glial cells. The results demonstrate a nuclear expression of CSTB in NSC and in neurons, suggesting novel function for this molecule.

Molecular background of progressive myoclonus epilepsy

Research on human inherited diseases provides a powerful tool to identify an intrinsically important subset of genes vital to healthy functioning of the organism. Progressive myoclonus epilepsies (PMEs) are a group of rare inherited disorders characterized by the association of epilepsy, myoclonus and progressive neurological deterioration. Significant progress has been made in elucidating the molecular background of PMEs. Here, progress towards understanding the molecular pathogenesis of PMEs is reviewed using the most common single cause of PME, Unverricht-Lundborg disease, as an example. Mutations in the gene encoding cystatin B (CSTB), a cysteine protease inhibitor, are responsible for the primary defect in Unverricht-Lundborg disease. CSTB-deficient mice, produced by targeted disruption of the mouse Cstb gene, display a phenotype similar to the human disease, with progressive ataxia and myoclonic seizures. The mice show neuronal atrophy, apoptosis and gliosis as well as increased expression of apoptosis and glial activation genes. Although significant advances towards understanding the molecular basis of Unverricht-Lundborg disease have been achieved, the physiological function of CSTB and the molecular pathogenesis of the disease remain unknown.

The human telomerase gene: complete genomic sequence and analysis of tandem repeat polymorphisms in intronic regions

In this work, the full-length hTERT gene was isolated and the sequence of the previously unknown region in intron 6 as well as that of upstream and downstream hTERT regions was determined. We have shown that intron 6 includes a variable number of tandem repeats (VNTR) of a 38 bp sequence, (hTERT-VNTR 6-1). Eight alleles of hTERT-VNTR 6-1 were identified among 103 unrelated individuals, ranging from 27 to 47 repeats. hTERT-VNTR 2-2 is another new 61 bp minisatellite repeat found in intron 2 of hTERT. At least four alleles of hTERT-VNTR 2-2 can be distinguished. Previous studies have described polymorphisms for minisatellites hTERT-VNTR 2-1, a 42 bp repeat in intron 2, and hTERT-VNTR 6-2, a 36 bp repeat in intron 6. These, together with another minisatellite found in intron 12, add up to five such structures within the hTERT gene. The segregation of hTERT minisatellites was analysed in families, revealing that the VNTRs are transmitted through meiosis following a Mendelian inheritance. Minisatellites in hTERT were also analysed in matching normal and cancer tissues from patients with tumors; in one patient with a kidney tumor, the two VNTRs in intron 6 had undergone concomitant rearrangements. This observation suggests that chromosomal rearrangements implicating these VNTRs may be associated with the activation of telomerase expression in cancer cells.

Inherited epilepsies

Epilepsy may be acquired or inherited. At least one half of epilepsy is genetic in origin; this figure is likely higher in children regardless of whether seizures are generalized or partial. Inherited epilepsies are classified as benign, cryptogenic, or symptomatic depending on associated clinical, electrographic, and neuroimaging features. To date, genetic mutations in the idiopathic inherited epilepsies affect channel function within the central nervous system; genes underlying symptomatic epilepsies are more heterogeneous. Accurate diagnosis of an inherited epilepsy syndrome provides useful prognostic information; it also may help guide diagnostic evaluation, including request for specific gene testing. In the near future, the relationship between genetic defect and response to specific anticonvulsants may also be better defined.

Identification and characterization of the human parkin gene promoter

Compound mutations and homozygous loss of function of the parkin gene causes juvenile and early onset, autosomal recessive parkinsonism. Pathologically, the disease is associated with loss of dopaminergic neurons in the substantia nigra pars compacta and locus ceruleus, usually without Lewy body pathology. Hemizygous families have been described that may harbor mutations outside of the open reading frame. The parkin gene promoter has yet to be characterized, and therein, mutations in hemizygous families may plausibly be identified. To identify the promoter of the parkin gene, the transcription start site was defined by a combination of primer extension and 5' RACE. Five kilobases of DNA 5' to the parkin start codon were directly sequenced from a BAC containing parkin exon 1 and evaluated for promoter motifs. The parkin promoter lacks TATA or CAAT boxes and appears to share homology to the alpha-synuclein promoter. Deletion constructs demonstrated core promoter activity and tissue specific enhancing regions in HEK-293T and SH-SY5Y cells.

Rearrangements of minisatellites in the human telomerase reverse transcriptase gene are not correlated with its expression in colon carcinomas

Telomerase activation is crucial in human carcinogenesis. The limiting component of telomerase, the catalytic subunit (hTERT), is undetectable in normal somatic cells but present in most tumor cells, including the earliest stages of colon carcinoma. The mechanisms involved in the differential expression in normal and tumor cells are not understood. In normal cells hTERT expression is shut down by a repressor, and upregulation could be a consequence of cis-acting changes in the hTERT gene, making it resistant to repression. We have identified a polymorphic and a monomorphic minisatellite in the second intron of the hTERT gene, and polymorphic one in intron 6. The polymorphic minisatellite in intron 2 contains binding sites for c-Myc, which has been shown to upregulate hTERT transcription. Screening colon carcinoma DNAs for rearrangements of hTERT minisatellites we detected no changes in 33 samples from tumors, most of which express hTERT. This indicates that size rearrangements of the hTERT minisatellites are not required for telomerase expression in colon carcinomas. Minor changes and one LOH were seen in five tumors.