Juvenile GM2 gangliosidosis caused by substitution of histidine for arginine at position 499 or 504 of the alpha-subunit of beta-hexosaminidase.
Juvenile GM2 gangliosidosis is a rare neurodegenerative disorder closely related to Tay-Sachs disease but of later onset and more protracted course. The biochemical defect lies in the alpha-subunit of the lysosomal enzyme beta-hexosaminidase. Cultured fibroblasts derived from patient A synthesized an alpha-subunit which could acquire mannose 6-phosphate and be secreted, but which failed to associate with the beta-subunit to form the enzymatically active heterodimer. By contrast, fibroblasts from patient B synthesized an alpha-subunit that was retained in the endoplasmic reticulum. To identify the molecular basis of the disorder, RNA from fibroblasts of these two patients was reverse-transcribed, and the cDNA encoding the alpha-subunit of beta-hexosaminidase was amplified by the polymerase chain reaction (PCR) in four overlapping fragments. The PCR fragments were subcloned and shown by sequence analysis to contain a G to A transition corresponding to substitution of histidine for arginine at position 504 in the case of patient A and at position 499 in the case of patient B. The mutations were confirmed by hybridization of allele-specific oligonucleotides to PCR-amplified fragments of DNA corresponding to exon 13 of the alpha-subunit gene. The Arg504----His mutation was found on both alleles of patient A as well as of another unrelated patient; the homozygosity of this mutant allele is attributable to consanguinity in the two families. The Arg499----His mutation was found in patient B in compound heterozygosity with a common infantile Tay-Sachs allele. There is additional heterogeneity in juvenile GM2 gangliosidosis, as neither mutation was found in the DNA of a fourth patient. The Arg----His mutations at positions 499 and 504 are located at CpG dinucleotides, which are known to be mutagenic "hot spots."
Paw
B H
BH
Department of Biological Chemistry, School of Medicine, University of California, Los Angeles 90024.
Moskowitz
S M
SM
Uhrhammer
N
N
Wright
N
N
Kaback
M M
MM
Neufeld
E F
EF
D001120:Arginine; D001483:Base Sequence; D002478:Cells, Cultured; D002648:Child; D002675:Child, Preschool; D004247:DNA / Q000235:genetics; D005260:Female; D005347:Fibroblasts / Q000201:enzymology; D005678:G(M2) Ganglioside; D005733:Gangliosidoses / Q000201:enzymology* / Q000235:genetics; D006639:Histidine; D006720:Homozygote; D006801:Humans; D008247:Lysosomes / Q000201:enzymology*; D046911:Macromolecular Substances; D008297:Male; D008969:Molecular Sequence Data; D009154:Mutation; D009693:Nucleic Acid Hybridization; D016133:Polymerase Chain Reaction; D014158:Transcription, Genetic; D001619:beta-N-Acetylhexosaminidases / Q000235:genetics*
D046911:Macromolecular Substances; D005678:G(M2) Ganglioside; D006639:Histidine; D004247:DNA; D001120:Arginine; D001619:beta-N-Acetylhexosaminidases