Action myoclonus-renal failure syndrome: diagnostic applications of activity-based probes and lipid analysis.

Lysosomal integral membrane protein-2 (LIMP2) mediates trafficking of glucocerebrosidase (GBA) to lysosomes. Deficiency of LIMP2 causes action myoclonus-renal failure syndrome (AMRF). LIMP2-deficient fibroblasts virtually lack GBA like the cells of patients with Gaucher disease (GD), a lysosomal storage disorder caused by mutations in the GBA gene. While GD is characterized by the presence of glucosylceramide-laden macrophages, AMRF patients do not show these. We studied the fate of GBA in relation to LIMP2 deficiency by employing recently designed activity-based probes labeling active GBA molecules. We demonstrate that GBA is almost absent in lysosomes of AMRF fibroblasts. However, white blood cells contain considerable amounts of residual enzyme. Consequently, AMRF patients do not acquire lipid-laden macrophages and do not show increased plasma levels of macrophage markers, such as chitotriosidase, in contrast to GD patients. We next investigated the consequences of LIMP2 deficiency with respect to plasma glycosphingolipid levels. Plasma glucosylceramide concentration was normal in the AMRF patients investigated as well as in LIMP2-deficient mice. However, a marked increase in the sphingoid base, glucosylsphingosine, was observed in AMRF patients and LIMP2-deficient mice. Our results suggest that combined measurements of chitotriosidase and glucosylsphingosine can be used for convenient differential laboratory diagnosis of GD and AMRF.

Chronic neuronopathic type of Gaucher's disease with progressive myoclonic epilepsy in the absence of visceromegaly and bone involvement.

INTRODUCTION: Gaucher's disease is a lysosomal storage disorder caused by the deficiency of glucocerebrosidase. Gaucher's disease has three clinical types: non-neuronopathic (Type 1), Acute Neuropathic (Type 2) and chronic neuronopathic (Type 3). The chronic neuronopathic (Type 3) is characterised by a variety of disease variants with onset in childhood with hepatomegaly, skeletal lesions and later slow horizontal saccades, treatment-resistant generalised tonic-clonic and myoclonic seizures, dementia, progressive spasticity, cognitive deterioration, ataxia and death in the second or third decade of life. CASE PRESENTATION: We describe a case of a 17-year-old girl who was born normally but subsequently developed treatment-refractory seizures at the age of nine with myoclonus, oculomotor apraxia, ataxia and cognitive decline. Enzyme activity of beta-glucocerebrosidase was found to be low without visceromegaly or bone involvement. CONCLUSION: Screening for lysosomal enzyme activity should be done in patients exhibiting features suggestive of progressive myoclonic epilepsy.

Mutations in NHLRC1 cause progressive myoclonus epilepsy.

Lafora progressive myoclonus epilepsy is characterized by pathognomonic endoplasmic reticulum (ER)-associated polyglucosan accumulations. We previously discovered that mutations in EPM2A cause Lafora disease. Here, we identify a second gene associated with this disease, NHLRC1 (also called EPM2B), which encodes malin, a putative E3 ubiquitin ligase with a RING finger domain and six NHL motifs. Laforin and malin colocalize to the ER, suggesting they operate in a related pathway protecting against polyglucosan accumulation and epilepsy.

A nonsense mutation in the LIMP-2 gene associated with progressive myoclonic epilepsy and nephrotic syndrome.

The main clinical features of two siblings from a consanguineous marriage were progressive myoclonic epilepsy without intellectual impairment and a nephrotic syndrome with a strong accumulation of C1q in capillary loops and mesangium of kidney. The biochemical analysis of one of the patients revealed a normal beta-glucocerebrosidase activity in leukocytes, but a severe enzymatic deficiency in cultured skin fibroblasts. This deficiency suggested a defect in the intracellular sorting pathway of this enzyme. The sequence analysis of the gene encoding LIMP-2 (SCARB2), the sorting receptor for beta-glucocerebrosidase, confirmed this hypothesis. A homozygous nonsense mutation in codon 178 of SCARB2 was found in the patient, whereas her healthy parents were heterozygous for the mutation. Besides lacking immunodetectable LIMP-2, patient fibroblasts also had decreased amounts of beta-glucocerebrosidase, which was mainly located in the endoplasmic reticulum, as assessed by its sensitivity to Endo H. This is the first report of a mutation in the SCARB2 gene associated with a human disease, which, contrary to earlier proposals, shares no features with Charcot-Marie-Tooth disease both at the clinical and neurophysiological levels.

Progressive myoclonus epilepsy in Gaucher Disease due to a new Gly-Gly mutation causing loss of an Exonic Splicing Enhancer.

BACKGROUND: Patients with Gaucher Disease (GD) exhibit three phenotypes, including type 1 (non-neuronopathic), type 2 (acute neuronopathic), and type 3 (subacute neuronopathic). AIM: Identifying which GBA changes represent benign polymorphisms and which may result in disease-causing mutations is essential for diagnosis and genotype/phenotype correlations but is often challenging. RESULTS: Here, we describe a patient with type 3 GD, presenting with drug-resistant epilepsy, who bears a set of GBA polymorphic variants including the novel c.363A > G (Gly82Gly) synonymous mutation. In silico predictions, mRNA and functional studies revealed that the new Gly82Gly mutation causes skipping of GBA exon 4, leading to a severe reduction of the wild type GBA mRNA. This is the first report of a synonymous change causing GD through loss of an exonic splicing enhancer sequence. The synonymous mutation is in trans with the Asn188Ser missense mutation, thus making the Asn188Ser responsible for the patient's phenotype and strengthening the association of Asn188Ser with the particular neurological phenotype of type 3 GD. CONCLUSION: We strengthen the association of Asn188Ser with the type 3 GD phenotype and progressive myoclonus epilepsy. Our data confirm that in silico predictions and mRNA analysis are mandatory in discriminating pathological mutations from the background of harmless polymorphisms, especially synonymous changes.

GSTA1, GSTM1, GSTP1 and GSTT1 polymorphisms in progressive myoclonus epilepsy: A Serbian case-control study.

PURPOSE: Oxidative stress is recognized as an important factor in progressive myoclonus epilepsy (PME). Genetic polymorphism of glutathione S-transferases (GSTs), which are involved in both protection from oxidative damage and detoxification, might alter the capacity for protecting tissues from exogenous and endogenous oxidants. We aimed to assess a possible association between GST polymorphism and PME, as well as, correlation between GST genotypes and oxidative phenotype in PME patients. METHODS: GSTA1, GSTM1, GSTP1 and GSTT1 genotypes were determined in 26 patients with PME and 66 controls. Byproducts of protein oxidative damage (thiol groups (P-SH) and nitrotyrosine), superoxide dismutase (SOD) and glutathione peroxidase (GPX) activities were determined. RESULTS: The frequency of GSTA1, GSTM1 and GSTP1 genotypes was not significantly different between PME patients and controls, while individuals with GSTT1-null genotype were at 5.44-fold higher risk of PME than carriers of GSTT1-active genotype. Moreover, significant risk of PME was obtained in carriers of both GSTT1-null and GSTM1-null genotypes. Carriers of combined GSTA1- active and GSTT1-null genotype were at highest, 7.55-fold increased risk of PME. Byproducts of protein damage did not reach statistical significance, while SOD and GPX activities were significantly higher in PME patients then in controls. When stratified according to GST genotype, P-SH groups were significantly lower only in patients with GSTT1-null genotype in comparison to carriers of active genotype. Only SOD activity was increased in GSTT1-null when compared to corresponding active genotype. CONCLUSIONS: GSTT1-null genotype might be associated with the increased risk and enhanced susceptibility to oxidative stress in PME patients.

Selective colocalization of transglutaminase-like activity in ubiquitinated intranuclear inclusions of hereditary dentatorubral-pallidoluysian atrophy.

To investigate the role of transglutaminase (TG) in the pathophysiology of dentatorubral-pallidoluysian atrophy (DRPLA), the distributions of ubiquitin-positive neuronal intranuclear inclusions (Ub-NII) and TG activity were studied in three patients with DRPLA and four disease controls. In the cerebellar granule cells of DRPLA, 2.5-4.9% of neurons had Ub-NII, and 7.5-9.8% of them were TG positive. In the frontal cortex; however, the ratio of neurons with Ub-NII was relatively low compared with those in the cerebellar cortex, and no Ub-NII was TG positive. There was no distinct difference in the ratio of neurons with Ub-NII and their TG positivity between the cases with homozygous or heterozygous DRPLA patients. The selective and good colocalization of Ub-NII and TG in the cerebellar granule cells may reveal a role of TG in the neurodegenerative process in DRPLA.

A novel SCARB2 mutation in progressive myoclonus epilepsy indicated by reduced ß-glucocerebrosidase activity.

Action myoclonus renal failure (AMRF) syndrome is a rare form of progressive myoclonus epilepsy with renal dysfunction related to mutations in the SCARB2 gene. This gene is involved in lysosomal mannose-6-phosphate-independent trafficking of ß-glucocerebrosidase (GC), an enzyme deficient in Gaucher disease. We report a family with myoclonic epilepsy, ataxia and skeletal muscle atrophy but without cognitive impairment or overt renal disease. A novel SCARB2 mutation was indicated by a striking discrepancy between lymphocyte and fibroblast GC activity in the proband evaluated for possible Gaucher disease. Our findings expand the genetic and phenotypic diversity of AMRF and suggest that low GC activity may present an important biochemical clue to the diagnosis of AMRF.

Early visual seizures and progressive myoclonus epilepsy in neuronopathic Gaucher disease due to a rare compound heterozygosity (N188S/S107L).

PURPOSE: Gaucher disease, the inherited deficiency of the lysosomal enzyme glucocerebrosidase, is characterized by genotypic and phenotypic heterogeneity. We recently characterized the glucocerebrosidase alleles of a patient with an unusual clinical presentation of type 3 Gaucher disease. METHODS: Initial clinical manifestations appeared at age 11 years as visual seizures. RESULTS: Subsequent progressive myoclonus and generalized seizures were consistent with an adolescent-onset form of progressive myoclonus epilepsy. However, a specific diagnosis was established only at age 16, because of the absence of hematologic abnormalities and a fairly moderate hepatomegaly. Bone marrow aspirate was slightly positive for Gaucher cells. Demonstration of reduced glucocerebrosidase in the fibroblasts confirmed the diagnosis. The child died at age 19 years. Postmortem sequencing of the glucocerebrosidase gene from cultured fibroblasts demonstrated a rare compound heterozygote for N188S/S107L. CONCLUSIONS: This unusual presentation of Gaucher disease indicates that if clinical and neurophysiological findings in adolescents with initial visual seizures and myoclonus suggest a progressive disorder, enzymatic assay is mandatory, even in the absence of the classic neurologic and systemic signs of the disease. Early differential diagnosis from other forms of progressive myoclonus epilepsy with similar clinical presentation may help provide appropriate genetic counseling.