Mucolipidosis type II a/b is a severe, autosomal recessive lysosomal storage disorder, caused by a defect in the GNPTAB gene that codes for the a/b subunits of the GlcNAc-phosphotransferase. To date, over 100 different mutations have been identified in MLII a/b patients, but no large deletions have been reported. Here we present the first case of a large homozygous intragenic GNPTAB gene deletion (c.3435-386_3602 + 343del897) encompassing exon 19, identified in a ML II a/b patient. Long-range PCR and sequencing methodologies were used to refine the characterization of this rearrangement, leading to the identification of a 21 bp repetitive motif in introns 18 and 19. Further analysis revealed that both the 5 0 and 3 0