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

Paulo Gaspar,Michael Schwake,Wouter W. Kallemeijn,Clara Sá Miranda,Anneke Strijland,Saskia Scheij,Herman S. Overkleeft,Jan Aten,Andrea Balreira,Marco Van Eijk,Friederike Zunke,JohannesM.F.G. Aerts

doi:10.1194/jlr.m043802

Abstract

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.

Highlights

Lysosomal integral membrane protein-2 (LIMP2) mediates trafficking of glucocerebrosidase (GBA) to lysosomes
We studied the consequences of LIMP2 deficiency for glucosylceramide and glucosylsphingosine levels, the products of hydrolysis by GBA
Soon afterwards Berkovic et al [17] demonstrated that LIMP2 deficiency due to mutations in the scavenger receptor class B member 2 (SCARB2) gene forms the basis for action myoclonus-renal failure syndrome (AMRF)

Summary

Introduction

Lysosomal integral membrane protein-2 (LIMP2) mediates trafficking of glucocerebrosidase (GBA) to lysosomes. 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. Plasma glucosylceramide concentration was normal in the AMRF patients investigated as well as in LIMP2-deficient mice. A marked increase in the sphingoid base, glucosylsphingosine, was observed in AMRF patients and LIMP2-deficient mice. The most common phenotype is the nonneuronopathic type 1 (MIM*230800), showing almost exclusive storage of glucosylceramide in tissue macrophages, the so-called “Gaucher cells” [1, 2] These lipid-laden macrophages accumulate in various tissues, such as spleen, liver, bone marrow and lung, resulting in clinical symptoms of which cytopenia, hepatosplenomegaly, and skeletal abnormalities are the most prominent [1]. The sphingoid base is likely formed from accumulating glucosylceramide in GBA-deficient cells. Epoxides like conduritol B epoxide (CBE) and cyclophellitol form a covalent bond

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Conclusion