Human Molecular Genetics, Vol 7, 1215-1219, Copyright © 1998 by Oxford University Press
JS Harvey, WF Carey and CP Morris
Metachromatic leukodystrophy (MLD) is an inborn error of myelin metabolism
caused by a deficiency of the lysosomal hydrolase, arylsulfatase A (ASA).
About 1% of the normal population have ASA activity levels approximating
those of MLD patients. This non- pathogenic reduction in ASA activity is
caused by homozygosity for the ASA pseudodeficiency allele (ASA-PD).
Although this allele contains two sequence alterations, a polyadenylation
defect and an amino acid substitution (N350S), the reduction in ASA
activity previously has been attributed to the polyadenylation defect which
reduces the amount of ASA mRNA and hence ASA protein by approximately 90%.
The identification of MLD patients who are homozygous for the ASA-PD allele
has brought about the need to re-evaluate the allele in light of the
possible role that it may play in the development and progression of
disease. Ribonuclease protection assay analysis of ASA mRNA transcripts and
an investigation into the activity and lysosomal localization of protein
expressed by an ASA expression construct containing the N350S variant
indicated that both the N350S and polyadenylation defects play a role in
biochemically defining the ASA-PD phenotype. The combined effect of the
reduction in ASA mRNA due to the polyadenylation defect and the lowering of
ASA activity and aberrant targeting of the expressed N350S ASA protein to
the lysosome is estimated to reduce ASA activity in pseudodeficiency
homozygotes to approximately 8% of normal.
ARTICLES
Importance of the glycosylation and polyadenylation variants in metachromatic leukodystrophy pseudodeficiency phenotype
Department of Chemical Pathology, Women's and Children's Hospital, North Adelaide, 5006, Australia.
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