Brief Communication
Biochemical and molecular findings in a patient with myoclonic epilepsy due to a mistarget of the β-glucosidase enzyme

https://doi.org/10.1016/j.ymgme.2009.04.011Get rights and content

Abstract

A deficiency of human LIMP-2, a receptor for lysosomal mannose 6-phosphate-independent targeting of the β-glucosidase (βGC), due to mutations in the SCARB2 gene was described only in six families presented with progressive myoclonic epilepsy and nephrotic syndrome. In one of them a mistarget of the βGC was demonstrated.

We report here the biochemical and molecular findings in a patient diagnosed with progressive myoclonic epilepsy due to a mistarget of the βGC, probably caused by a LIMP-2 deficiency, providing valuable information for the diagnosis of this rare disorder.

Introduction

β-Glucosidase (βGC), a lysosomal enzyme defective in most cases of Gaucher disease (GD) [1], is target to the lysosomes through a mannose 6-phosphate receptor independent mechanism. It has been shown that the lysosomal integral membrane protein type 2 (LIMP-2), an ubiquitously expressed trans membrane protein [2] mainly found in the lysosomes and late endosomes [3], is a receptor for lysosomal mannose 6-phosphate-independent targeting of the βGC [4].

In fact, in the LIMP-2 deficient mouse the missorting of the βGC results in a reduction of intracellular βGC activity and protein levels. The phenotype is characterized by neurological and renal involvement [4].

In humans, LIMP-2 is encoded by the SCARB2 gene located on chromosome 4q13-21 [4]. Recently, an autosomal recessive disorder caused by deficiency of human LIMP-2 due to mutations in the SCARB2 gene was described in six unrelated families, three from Australia, two from Canada and one from Portugal. All of them presented with symptoms of action myoclonus-renal failure syndrome [5], [6], [7].

In this report the biochemical and molecular findings in an Italian patient affected with myoclonic epilepsy due to a mistarget of the β-glucosidase enzyme are discussed.

Section snippets

Case report

The patient is a 29-year-old female presenting with progressive myoclonic epilepsy without intellectual impairment. She manifested the first neurological symptoms at the age of 26, when she started to experience anxiety and myoclonic jerks of the lower limbs. The symptoms rapidly progressed to generalized tremors, hypotonia, ataxia and progressively worsening action myoclonus, prominent on the right upper limb. At the age of 27 she presented a single convulsive seizure and loss of

Enzyme activity assay and filipin staining

Acid β-glucosidase activity was measured using the fluorogenic substrate 4-methylumbelliferyl-β-d-glucopyranoside (Sigma, St. Louis, MO, USA) in the presence of sodium deoxytaurocholate [8].

Plasmatic chitotriosidase activity was determined using the fluorogenic substrate 4 MU-chitotrioside [9].

Filipin staining was performed using the method described by Blanchette-Mackie et al. [10].

Mutational analysis

Genomic DNA was extracted from peripheral blood leukocytes with QIAamp DNA blood Mini Kit (Qiagen GmbH, Hilden,

Results and discussion

The clinical picture of the patient prompted us to hypothesize the possible metabolic origin of the disease.

In particular, Niemann Pick type C (NPC) [12] and chronic neuronopathic GD (GD type III) [13] were considered, even if no signs of organomegaly and hematological involvement (anemia, thrombocytopenia) were evident.

Filipin staining assay clearly showed the absence of intracellular cholesterol accumulation, ruling out the diagnosis of NPC disease.

In order to determine whether the patient

Acknowledgments

The samples (patient and control subjects) were obtained from the “Cell Line and DNA Bank from Patients affected by Genetic Diseases” (G. Gaslini Institute) part of Telethon Genetic Biobank Network (Project No. GTB07001A). We gratefully acknowledge Sarah Tripepi Winteringham for her assistance with the editing of the manuscript.

References (13)

There are more references available in the full text version of this article.

Cited by (28)

  • Identification and characterization of scavenger receptor class B member 2 in Nile tilapia (Oreochromis niloticus)

    2021, Aquaculture Reports
    Citation Excerpt :

    It is becoming that scarb2 has several discrete functions. It is now appreciated that the protein is involved in general lysosomal maintenance (Kuronita et al., 2002), serves as a receptor for GCase (Dardis et al., 2009; Reczek et al., 2007), and is critical receptor for enterovirus 71 (EV71) strains and Coxsackieviruses (Yamayoshi et al., 2012, 2009; Yamayoshi and Koike, 2011). Defects in scarb2 have been linked to a number of diseases (Berkovic et al., 2008; Schroen et al., 2007; Yamayoshi and Koike, 2011).

  • Glucosylceramidases and malignancies in mammals

    2016, Biochimie
    Citation Excerpt :

    Genetic defects in LIMP-2 (SCARB2 gene) are not responsible for a GD phenotype but a severe autosomal recessive disorder known as action myoclonus-renal failure syndrome (MIM# 254900) [72]. It associates progressive myoclonic epilepsy with storage material in the brain, and focal glomerulosclerosis with reduced GlcCerase activity in fibroblasts [73]. LIMP-2 could serve as a modifier in GD [74].

  • Scavenger Receptors

    2016, Encyclopedia of Cell Biology
  • A novel SCARB2 mutation in progressive myoclonus epilepsy indicated by reduced β-glucocerebrosidase activity

    2014, Journal of the Neurological Sciences
    Citation Excerpt :

    Gene expression assays using real-time RT-PCR indicated > 80% reduction in the SCARB2 expression in the patient as compared to control (Fig. 3). After ruling out mutations in the GBA and PSAP, the striking discrepancy between lymphocyte and fibroblast GC activity in the proband indicated the possibility of a SCARB2-related disease [4,11–14]. Previously, SCARB2 mutations were identified mostly on the basis of clinical presentation, and this is the third report of a patient diagnosed as a result of initial testing for Gaucher disease [12,13,15].

  • Lysosomal integral membrane protein-2: A new player in lysosome-related pathology

    2014, Molecular Genetics and Metabolism
    Citation Excerpt :

    When GCase activity was measured, it was found that although patient fibroblasts only had 10% of control GCase activity, leukocytes and plasma showed normal activity levels, suggesting that there may be a secondary targeting mechanism by which GCase is transported to lysosomes [63]. A similar patient with PME that was heterozygous for the LIMP-2 mutation H363N had onset of symptoms at 26 years consisting of myoclonus, tremors, and ataxia [51]. In contrast to the siblings, this patient had normal GCase activity in fibroblasts [51].

View all citing articles on Scopus
View full text