Sanfilippo A syndrome (MPS-IIIA) is a mucopolysaccharide lysosomal storage disorder caused by a deficiency in the lysosomal enzyme, sulphamidase (EC 3.10.1.1), which is required for the degradation of heparan sulphate. A genomic clone containing the entire sulphamidase gene was isolated from a chromosome 17-specific gridded cosmid library. The structure of the gene and the sequence of the exon/intron boundaries and the 5' promoter region were determined. The sulphamidase gene is split into 8 exons spanning approximately 11 kb.