Table 2.

Beta-Galactosidase Enzyme Activity in GLB1-Related Disorders by Phenotype

GM1 GangliosidosisMPS IVB
Type IType IIType III
InfantileLate infantileJuvenileChronic/Adult
Beta-galactosidase
enzyme activity 1, 2 		Negligible~1%-5%~3%-10%5%-10%2%-12%
1.

Relative values (% of normal activity)

2.

Although the percent of residual enzyme activity correlates generally with phenotype, it cannot predict the type of GM1 gangliosidosis. The lack of direct correlation between enzyme activity and disease severity may be due to the use of artificial substrates in the in vitro enzyme assay, which may not exactly replicate in vivo enzyme activity with natural substrates. Modifier genes could theoretically alter enzyme activity and thus, disease severity.

From: GLB1-Related Disorders

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