CSTB gene replacement improves neuroinflammation, neurodegeneration and ataxia in murine type 1 progressive myoclonus epilepsy.

EPM1 is the most common form of Progressive Myoclonus Epilepsy characterized by late-childhood onset, ever-worsening and disabling myoclonus, seizures, ataxia, psychiatric disease, and shortened lifespan. EPM1 is caused by expansions of a dodecamer repeat sequence in the promoter of CSTB (cystatin B), which dramatically reduces, but does not eliminate, gene expression. The relatively late onset and consistent presence of a minimal amount of protein product makes EPM1 a favorable target for gene replacement therapy. If treated early, these children's normally developed brains could be rescued from the neurodegeneration that otherwise follows, and their cross-reactive immunological material (CRIM) positive status greatly reduces transgene related toxicity. We performed a proof-of-concept CSTB gene replacement study in Cstb knockout mice by introducing full-length human CSTB driven by the CBh promoter packaged in AAV9 and administered at postnatal days 21 and 60. Mice were sacrificed at 2 or 9 months of age, respectively. We observed significant improvements in expression levels of neuroinflammatory pathway genes and cerebellar granule cell layer apoptosis, as well as amelioration of motor impairment. The data suggest that gene replacement is a promising therapeutic modality for EPM1 and could spare affected children and families the ravages of this otherwise severe neurodegenerative disease.

Berardinelli-Seip syndrome and progressive myoclonus epilepsy.

Berardinelli-Seip syndrome, or congenital generalized lipodystrophy type 2 (CGL2), is characterized by a lack of subcutaneous adipose tissue and precocious metabolic syndrome with insulin resistance, resulting in diabetes, dyslipidaemia, hepatic steatosis, cardiomyopathy, and acanthosis nigricans. Most reported mutations are associated with mild, non-progressive neurological impairment. We describe the clinical and EEG data of a patient with progressive myoclonus epilepsy (PME), CGL2, and progressive neurological impairment, carrying a homozygous BSCL2 nonsense mutation. The patient had epilepsy onset at the age of two, characterized by monthly generalized tonic-clonic seizures. By the age of three, he presented with drug-resistant ongoing myoclonic absence seizures, photosensitivity, progressive neurological degeneration, and moderate cognitive delay. Molecular analysis of the BSCL2 gene yielded a homozygous c.(1076dupC) p.(Glu360*) mutation. Application of a vagus nerve stimulator led to temporary improvement in seizure frequency, general neurological condition, and EEG background activity. Specific BSCL2 mutations may lead to a peculiar CGL2 phenotype characterized by PME and progressive neurodegeneration. Application of a vagus nerve stimulator, rarely used for PMEs, may prove beneficial, if only temporarily, for both seizure frequency and general neurological condition.

Acid ceramidase deficiency: Farber disease and SMA-PME.

Acid ceramidase (ACDase) deficiency is a spectrum of disorders that includes a rare lysosomal storage disorder called Farber disease (FD) and a rare epileptic disorder called spinal muscular atrophy with progressive myoclonic epilepsy (SMA-PME). Both disorders are caused by mutations in the ASAH1 gene that encodes the lysosomal hydrolase that breaks down the bioactive lipid ceramide. To date, there have been fewer than 200 reported cases of FD and SMA-PME in the literature. Typical textbook manifestations of classical FD include the formation of subcutaneous nodules, accumulation of joint contractures, and development of a hoarse voice. In reality, however, the clinical presentation is much broader. Patients may develop severe pathologies leading to death in infancy or may develop attenuated forms of the disorder wherein they are often misdiagnosed or not diagnosed until adulthood. A clinical variability also exists for SMA-PME, in which patients develop progressive muscle weakness and seizures. Currently, there is no known cure for FD or for SMA-PME. The main treatment is symptom management. In rare cases, treatment may include surgery or hematopoietic stem cell transplantation. Research using disease models has provided insights into the pathology as well as the role of ACDase in the development of these conditions. Recent studies have highlighted possible biomarkers for an effective diagnosis of ACDase deficiency. Ongoing work is being conducted to evaluate the use of recombinant human ACDase (rhACDase) for the treatment of FD. Finally, gene therapy strategies for the treatment of ACDase deficiency are actively being pursued. This review highlights the broad clinical definition and outlines key studies that have improved our understanding of inherited ACDase deficiency-related conditions.

Polyglutamine (PolyQ) diseases: genetics to treatments.

The polyglutamine (polyQ) diseases are a group of neurodegenerative disorders caused by expanded cytosine-adenine-guanine (CAG) repeats encoding a long polyQ tract in the respective proteins. To date, a total of nine polyQ disorders have been described: six spinocerebellar ataxias (SCA) types 1, 2, 6, 7, 17; Machado-Joseph disease (MJD/SCA3); Huntington's disease (HD); dentatorubral pallidoluysian atrophy (DRPLA); and spinal and bulbar muscular atrophy, X-linked 1 (SMAX1/SBMA). PolyQ diseases are characterized by the pathological expansion of CAG trinucleotide repeat in the translated region of unrelated genes. The translated polyQ is aggregated in the degenerated neurons leading to the dysfunction and degeneration of specific neuronal subpopulations. Although animal models of polyQ disease for understanding human pathology and accessing disease-modifying therapies in neurodegenerative diseases are available, there is neither a cure nor prevention for these diseases, and only symptomatic treatments for polyQ diseases currently exist. Long-term pharmacological treatment is so far disappointing, probably due to unwanted complications and decreasing drug efficacy. Cellular transplantation of stem cells may provide promising therapeutic avenues for restoration of the functions of degenerative and/or damaged neurons in polyQ diseases.

Pathological accumulation of atrophin-1 in dentatorubralpallidoluysian atrophy.

Dentatorubral-pallidoluysian atrophy (DRPLA) is caused by the expansion of polyglutamine (polyQ) in atrophin-1 (ATN1), also known as DRPLA protein. ATN1 is ubiquitously expressed in the central nervous system (CNS), although selective regions of CNS are degenerated in DRPLA, and this selective neuronal damage gives rise to the specific clinical features of DRPLA. Accumulation of mutant ATN1 that carries an expanded polyQ tract seems to be the primary cause of DRPLA neurodegeneration, but it is still unclear how the accumulation of ATN1 leads to neu-rodegeneration. Recently, cleaved fragments of ATN1 were shown to accumulate in the disease models and the brain tissues of patients with DRPLA. Furthermore, proteolytic processing of ATN1 may regulate the intracellular localization of ATN1 and its fragments. Therefore, proteolytic processing of ATN1 may provide clues to disease pathogenesis and hopefully aid in the determination of molecular targets for effective therapeutic approaches for DRPLA.

Impaired autophagy: a link between neurodegenerative diseases and progressive myoclonus epilepsies.

In recent years, research into the molecular bases of neurodegenerative diseases has progressed, and therapies have been developed to combat the causative agents. Based on the observation that progressive myoclonus epilepsies (PMEs) and neurodegenerative diseases share common features of neurodegeneration, we propose that the two pathologies share common underlying molecular characteristics. It is well documented that autophagy is overloaded or impaired in neurodegenerative conditions, and it is also impaired in some PMEs, the clearest example being EPM2 (Lafora disease). Although more research into this connection is warranted, we propose that existing therapies for PMEs could be augmented with similar drugs as those used for neurodegenerative diseases.

[From gene to disease; progressive myoclonus epilepsy of Unverricht-Lundborg and mutations in the cystatin B gene]. / Van gen naar ziekte; progressieve myoclonusepilepsie van Unverricht-Lundborg en mutaties in het cystatine-B-gen.

Progressive myoclonus epilepsy type 1 of Unverricht-Lundborg (EPM1) is a rare disorder, associated with mutations in the cystatin B (CSTB) gene. The most prevalent molecular abnormality is an expansion of a dodecamer repeat in the promoter region of the CSTB gene, but point mutations in the CSTB gene have also been found. DNA examination may be useful in discriminating EPM1 from juvenile myoclonic epilepsy, and from other types of progressive myoclonus epilepsy. An early diagnosis is important to optimise treatment and to provide an adequate prognosis and prediction of recurrence.