α-Mannosidosis - An underdiagnosed lysosomal storage disease in individuals with an 'MPS-like' phenotype.

Individuals affected by alpha-Mannosidosis suffer from similar clinical symptoms such as respiratory infections, skeletal changes as patients with mucopolysaccharidoses (MPS). α-Mannosidosis is considered as an ultra-rare disorders and also diagnostic testing is often limited. With the availability of novel therapies and easy-to-access diagnostic tests (e.g. Tandem mass spectrometry) using dried blood spots for both enzymatic and genetic testing, the chance for the development of a better understanding of disease and awareness may be triggered. In a pilot study, we have investigated 1010 residual dried blood spot samples from individuals suspicious to MPS. In these study cohort, 158/1010 individuals were genetically confirmed for MPS. Additional biochemical and genetic confirmatory testing for α-mannosidases revealed four individuals with a final diagnosis of α-mannosidosis. This unexpected high number of individuals with α-mannosidosis demonstrated the urgent need of taking this rare disorder in clinical and diagnostic consideration particularly in patients suspicious to MPS.