beta-Mannosidosis is a lysosomal storage disorder caused by deficiency of beta-mannosidase. Thirteen families with cases of beta-mannosidosis have been described including one case previously reported by our group. We present clinical and biochemical data in a new adult case, and the molecular analyses in both this new case and the one previously reported. We detected four novel mutations: p.R182W, p.G392E, p.W466X and c.1848delA. Discrepancies between genomic DNA and cDNA results when detecting this last deletion suggested a nonsense-mediated decay cell process (NMD).