The molecular lesion in the alpha-N-acetylgalactosaminidase gene that causes angiokeratoma corporis diffusum with glycopeptiduria.
Angiokeratoma corporis diffusum with glycopeptiduria is a recently recognized inborn error of glycoprotein catabolism resulting from the deficient activity of human alpha-N-acetylgalactosaminidase (E.C. 3.2.1.49; alpha-GalNAc). The first patient with this autosomal recessive disorder, a 46-yr-old consanguineous Japanese woman, presented with diffuse angiokeratoma, mild intellectual impairment, and peripheral neuroaxonal degeneration. Deficient alpha-GalNAc activity also has been reported in consanguineous brothers with an infantile-onset form of neuroaxonal dystrophy resulting from a missense mutation (designated E325K) in the alpha-GalNAc gene. To identify the mutation causing the phenotypically distinct adult-onset disorder, Southern and Northern hybridization analyses of DNA and RNA from the affected homozygote were performed which revealed a grossly normal alpha-GalNAc gene structure and normal transcript size and abundancy. Reverse transcription, amplification, and sequencing of the alpha-GalNAc transcript identified a single C to T transition at nucleotide (nt) 985 that predicted an arginine to tryptophan substitution in residue 329 (designated R329W) of the alpha-GalNAc polypeptide. This base substitution was confirmed by hybridization of PCR-amplified genomic DNA from family members with allele-specific oligonucleotides. Transient expression of an alpha-GalNAc construct containing the R329W mutation resulted in the expression of an immunoreactive polypeptide which had no detectable alpha-GalNAc activity. Comparison of the biosynthesis and stabilities of the transiently expressed and radiolabeled normal, E325K (infantile-onset) and R329W (adult-onset) alpha-GalNAc polypeptides in COS-1 cells indicated that both the mutant precursors were processed to the mature form; however, the E325K mutant polypeptide was more rapidly degraded than the R329W subunit, thereby providing a basis for the distinctly different infantile- and adult-onset phenotypes.
Department of Human Genetics, Mount Sinai School of Medicine, New York, NY 10029.
A M
AM
Wang
T
T
Kanzaki
R J
RJ
Desnick
D001483:Base Sequence; D002460:Cell Line; D000795:Fabry Disease / Q000235:genetics*; D005260:Female; D006020:Glycopeptides / Q000652:urine*; D006596:Hexosaminidases / Q000737:chemistry / Q000235:genetics*; D006801:Humans; D008969:Molecular Sequence Data; D009154:Mutation; D048809:alpha-N-Acetylgalactosaminidase
D006020:Glycopeptides; D006596:Hexosaminidases; C482722:NAGA protein, human; D048809:alpha-N-Acetylgalactosaminidase