Figure 1.

Correlation between residual β-galactosidase activity and clinical onset. The amount of residual enzyme activity shows positive correlation with the age of onset in various phenotypic forms of β-galactosidase deficiency disorders. Theoretically at least 10% of normal enzyme activity is necessary for washout of the storage substrate. The age of onset in patients expressing enzyme activity above this level will be beyond the human life span. See the text for more details. Reproduced from ref. 19 with minor modifications.