Relationship between blood enzyme level and substrate reduction expressed mathematically. With higher enzyme levels, there is better substrate reduction. At high enzyme levels, there is no further reduction is substrate so that enzyme is no longer limiting. This curve relates kidney metabolic correction, in which residual substrate is measured as the ratio of accumulated dermatan sulfate to nonaccumulated chondroitin sulfate,¹⁸  to blood enzyme, which is expressed as the average of a years' readings in a stably engrafted patient after HSCT. Similar curves could theoretically be constructed for other organs. Where correction is currently suboptimal in certain diseases and in certain organs, it might be improved by increasing the blood enzyme level. This is the basis for proposed lentiviral gene therapy of certain intractable LSDs.