Lysosomal multienzymatic complex-related diseases: a genetic study among Portuguese patients.

[gm1 gangliosidosis]

The functional activity of lysosomal enzymes sialidase , β-galactosidase and N-acetylaminogalacto-6 -sulfate-sulfatase in the cell depends on their association in a multienzyme complex with cathepsin A . Mutations in any of the components of this complex result in functional deficiency thereby causing severe lysosomal storage disorders . Here , we report the molecular defects underlying sialidosis (mutations in sialidase ; gene NEU 1 ), galactosialidosis (mutations in cathepsin A ; gene PPGB ) and GM 1 gangliosidosis (mutations in β-galactosidase ; gene GLB 1 ) in Portuguese patients . We performed molecular studies of the PPGB , NEU 1 and GLB 1 genes in biochemically diagnosed Portuguese patients . Gene expression was determined and the effect of each mutation predicted at protein levels . In the NEU 1 gene , we found three novel missense mutations (p .P 200 L , p .D 234 N and p .Q 282 H ) and one nonsense mutation (p .R 341 X ). In the PPGB gene , we identified two missense mutations , one novel (p .G 8 6 V ) and one already described (p .V 104 M ), as well as two new deletions (c .230 delC and c .991 -992 delT ) that give rise to non-functional proteins . We also present the first molecular evidence of a causal missense mutation localized to the cathepsin A active site . Finally , in the GLB 1 gene , we found six different mutations , all of them previously described (p .R 59 H , p .R 201 H , p .H 281 Y , p .W 527 X , c .1572 -1577 InsG and c .845 -846 delC ). Seven novel mutations are reported here , contributing to our knowledge of the mutational spectrum of these diseases and to a better understanding of the genetics of the lysosomal multienzymatic complex . The results of this study will allow carrier detection in affected families and prenatal molecular diagnosis , leading to the improvement of genetic counseling .