A MANBAmutation resulting in residual beta-mannosidase activity associated with severe leukoencephalopathy: a possible pseudodeficiency variantReport as inadecuate




A MANBAmutation resulting in residual beta-mannosidase activity associated with severe leukoencephalopathy: a possible pseudodeficiency variant - Download this document for free, or read online. Document in PDF available to download.

BMC Medical Genetics

, 10:84

First Online: 03 September 2009Received: 07 April 2009Accepted: 03 September 2009

Abstract

Backgroundβ-Mannosidosis OMIM 248510 is a rare inborn lysosomal storage disorder caused by the deficient activity of β-mannosidase, an enzyme encoded by a single gene MANBA located on chromosome 4q22-25. To date, only 20 cases of this autosomal recessive disorder have been described and 14 different MANBA mutations were incriminated in the disease. These are all null mutations or missense mutations that abolish β-mannosidase activity. In this study, we characterized the molecular defect of a new case of β-mannosidosis, presenting with a severe neurological disorder.

MethodsGenomic DNA was isolated from peripheral blood leukocytes of the patient to allow MANBA sequencing. The identified mutation was engineered by site-directed mutagenesis and the mutant protein was expressed through transient transfection in HEK293T cells. The β-mannosidase expression and activity were respectively assessed by Western blot and fluorometric assay in both leukocytes and HEK293T cells.

ResultsA missense disease-associated mutation, c.1922G>A p.Arg641His, was identified for which the patient was homozygous. In contrast to previously described missense mutations, this substitution does not totally abrogate the enzyme activity but led to a residual activity of about 7% in the patient-s leukocytes, 11% in lymphoblasts and 14% in plasma. Expression studies in transfected cells also resulted in 7% residual activity.

ConclusionCorrelations between MANBA mutations, residual activity of β-mannosidase and the severity of the ensuing neurological disorder are discussed. Whether the c.1922G>A mutation is responsible for a yet undescribed pseudodeficiency of β-mannosidase is also discussed.

AbbreviationsHEKhuman embryonic kidney cells

wtwild-type.

Electronic supplementary materialThe online version of this article doi:10.1186-1471-2350-10-84 contains supplementary material, which is available to authorized users.

Frédérique Sabourdy, Pierre Labauge contributed equally to this work.

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Author: Frédérique Sabourdy - Pierre Labauge - Hilde Monica Frostad Riise Stensland - Michèle Nieto - Violeta Latorre Garcés

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