Sanfilippo syndrome type B, or mucopolysaccharidosis (MPS) IIIB, is an autosomal recessive disease caused by a deficiency of lysosomal α-N-acetylglucosaminidase (NAGLU). In Dromaius novaehollandiae (emu), a progressive neurologic disease was recently discovered, which was characterized by NAGLU deficiency and heparan sulfate accumulation. To define the molecular basis, the sequences of the normal emu NAGLU cDNA and gene were determined by PCR-based approaches using primers for highly conserved regions of evolutionarily distant NAGLU homologues. It was observed that the emu NAGLU gene is structurally similar to that of human and mouse, but the introns are considerably shorter. The cDNA had an open reading frame (ORF) of 2259 bp. The deduced amino acid sequence is estimated to share 64% identity with human, 63% with mouse, 41% with Drosophila, 39% with tobacco, and 35% with the Caenorhabditis elegans enzyme. Three normal and two affected emus were studied for nucleotide sequence covering the entire coding region and exon-intron boundaries. Unlike the human gene, emu NAGLU appeared to be highly polymorphic: 19 variations were found in the coding region alone. The two affected emus were found to be homozygous for a 2-bp deletion, 1098-1099delGG, in exon 6. The resulting frameshift predicts a longer ORF of 2370 bp encoding a polypeptide with 37 additional amino acids and 387 altered amino acids. The availability of mutation screening in emus now permits early detection of MPS IIIB in breeding stocks and is an important step in characterizing this unique, naturally occurring avian model for the development of gene transfer studies.
Bibliographical noteFunding Information:
We thank H. L. Shivaprasad (University of California, Davis, CA), G. A. Bradley (University of Arizona, Tucson, AZ), Z. Parker (Quarry-ville, PA), and P. and G. Constans (Ta-Ha-Nee Mara Ranch, Nevis, MN) for tissue samples; the Microchemical Facility of the University of Minnesota (E. D. Eccleston) for synthesis of oligonucleotides; the Biomedical Imaging and Processing Laboratory of the University of Minnesota (G. J. Sedgewick) for help with preparation of figures; and L. B. Augustin for suggestions in computational analysis. This work was supported by the Children’s Medical Research Foundation (Susan and Brad Wilson, co-founders, Evanston, IL) and NIH grants from NICHD (P01-HD32652) and NCRR (RR02512).