Identification of two novel arylsulfatase A mutations with a polymorphism as a cause of metachromatic leukodystrophy.
OBJECTIVE
Metachromatic leukodystrophy is a lysosomal storage disorder caused by the deficiency of arylsulfatase A or saposin B. Enzyme deficiency leads to the accumulation of sulfatide, which results in severe demyelination.


METHODS
In this study, clinically suspected patients were diagnosed as metachromatic leukodystrophy by enzyme analysis using p-nitrocathecol sulfate as substrate. Eight exons and flanking regions of arylsulfatase A gene of patients were amplified by polymerase chain reaction and then subjected to single stranded conformational polymorphism analysis. Polymerase chain reaction products of suspicious exons in single stranded conformational polymorphism were purified from agarose gel and sequenced.


RESULTS
DNA sequencing revealed two novel disease-causing missense mutations: the first one is 1568G-->A, 307Glu-->Lys in exon 5 which is together with a 2161C-->T, 391Thr-->Ser polymorphism in exon 7; and the second one is 1603G-->T, 318Trp-->Cys in exon 5.


CONCLUSIONS
These two mutations are in highly conserved structural elements region of the arylsulfatase A protein. Thus, missense mutations 307Glu-->Lys in exon 5 and 318Trp-->Lys in exon 5 probably change the active site conformation by disrupting the sixth alpha helix and the twelfth beta-sheet structure of the arylsulfatase A protein, respectively, and cause deficiency in enzyme activity. This study provides the molecular basis for understanding the mechanism underlying metachromatic leukodystrophy.
Onder
Evren
E
Department of Biochemistry, Hacettepe University Faculty of Medicine, 06100 Ankara, Turkey.
Sinici
Incilay
I
Müjgan Sönmez
F
F
Topçu
Meral
M
Ozkara
H Asuman
HA