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beta-Mannosidosis caused by a novel homozygous intragenic inverted duplication in MANBA

Journal article
Authors Maria K. Blomqvist
M. F. Smeland
J. Lindgren
P. Sikora
Hmfr Stensland
Jorge Asin-Cayuela
Published in Cold Spring Harbor Molecular Case Studies
Volume 5
Issue 3
ISSN 2373-2873
Publication year 2019
Published at Institute of Biomedicine, Department of Clinical Chemistry and Transfusion Medicine
Language en
Keywords angiokeratoma-corporis-diffusum, deficiency, identification, fibroblasts, metabolism, leukocytes, mutation, variant, cdna
Subject categories Medical Genetics


beta-Mannosidosis is a lysosomal storage disorder characterized by accumulation of disaccharides due to deficiency of the lysosomal enzyme beta-mannosidase. The disease is caused by mutations in MANBA and is extremely rare in humans. Although the clinical presentation is heterogeneous, common symptoms include various degrees of developmental delay, behavioral disturbances, hearing loss, and frequent infections. We report a 15-yr-old girl presenting with mild intellectual disability, sensorineural hearing loss, severe behavioral disturbances, dysmorphic traits, and evolving angiokeratomas. Copy-number variation analysis of next-generation sequencing (NGS) data indicated increased coverage in exons 8-11 of MANBA. Low beta-mannosidase activity (1 mu katal/kg protein, refv 25-40) established the diagnosis of beta-mannosidosis. Whole-genome sequencing (WGS) and cDNA analysis revealed a novel homozygous intragenic inverted duplication in MANBA, where a 13.1-kb region between introns 7 and 11 was duplicated and inserted in an inverted orientation, creating a 67-base nonduplicated gap at the insertion point. Both junctions showed micro-homology regions. The inverted duplication resulted in exon skipping of exons 8-9 or 8-10. Our report highlights the importance of copy-number variation analysis of data from NGS and in particular the power of WGS in the identification and characterization of copy-number variants.

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