A method of compiling a treatment reference table that indicates the responsiveness of one or more specific mutations of α-Gal A to a specific pharmacological chaperone, the method comprising: i. analysing in vitro the response to the specific pharmacological chaperone in a host cell that has been transformed with a nucleic acid vector that encodes a first mutant α-Gal A by a method comprising: a. incubating first host cells with the specific pharmacological chaperone; b. measuring the α-Gal A activity in the host cells c. comparing the measured α-Gal A activity in lysates from the first host cells with measured α-Gal A in lysates from second host cells not treated with the specific pharmacological chaperone; and d. determining whether the first mutant α-Gal A is responsive to treatment with the specific pharmacological chaperone; ii. repeating steps (a) to (d) for second and further mutations of α-Gal A, iii. compiling a table listing responsive and non-responsive mutant forms of α-Gal A, wherein the specific pharmacological chaperone is 1-deoxygalactonojirimycin or a pharmaceutically salt or ester thereof; the first and second host cells are HEK-293 MSR cells; and a mutant α-Gal A is defined as responsive to treatment with the pharmacological chaperone if: there is a 1.3 to 40-fold increase in α-Gal A activity in the first host cells compared with the α-Gal A activity in the second host cells; or α-Gal A activity in the first host cells is at least about 2 to 100% of α-Gal A activity of HEK-293 MSR cells which express a wild type α-Gal A. i. analysing in vitro the response to the specific pharmacological chaperone in a host cell that has been transformed with a nucleic acid vector that encodes a first mutant α-Gal A by a method comprising: a. incubating first host cells with the specific pharmacological chaperone; b. measuring the α-Gal A activity in the host cells c. comparing the measured α-Gal A activity in lysates from the first host cells with measured α-Gal A in lysates from second host cells not treated with the specific pharmacological chaperone; and d. determining whether the first mutant α-Gal A is responsive to treatment with the specific pharmacological chaperone; a. incubating first host cells with the specific pharmacological chaperone; b. measuring the α-Gal A activity in the host cells c. comparing the measured α-Gal A activity in lysates from the first host cells with measured α-Gal A in lysates from second host cells not treated with the specific pharmacological chaperone; and d. determining whether the first mutant α-Gal A is responsive to treatment with the specific pharmacological chaperone; ii. repeating steps (a) to (d) for second and further mutations of α-Gal A, iii. compiling a table listing responsive and non-responsive mutant forms of α-Gal A, wherein the specific pharmacological chaperone is 1-deoxygalactonojirimycin or a pharmaceutically salt or ester thereof; the first and second host cells are HEK-293 MSR cells; and a mutant α-Gal A is defined as responsive to treatment with the pharmacological chaperone if: there is a 1.3 to 40-fold increase in α-Gal A activity in the first host cells compared with the α-Gal A activity in the second host cells; or α-Gal A activity in the first host cells is at least about 2 to 100% of α-Gal A activity of HEK-293 MSR cells which express a wild type α-Gal A. wherein the specific pharmacological chaperone is 1-deoxygalactonojirimycin or a pharmaceutically salt or ester thereof; the first and second host cells are HEK-293 MSR cells; and a mutant α-Gal A is defined as responsive to treatment with the pharmacological chaperone if: there is a 1.3 to 40-fold increase in α-Gal A activity in the first host cells compared with the α-Gal A activity in the second host cells; or α-Gal A activity in the first host cells is at least about 2 to 100% of α-Gal A activity of HEK-293 MSR cells which express a wild type α-Gal A. there is a 1.3 to 40-fold increase in α-Gal A activity in the first host cells compared with the α-Gal A activity in the second host cells; or α-Gal A activity in the first host cells is at least about 2 to 100% of α-Gal A activity of HEK-293 MSR cells which express a wild type α-Gal A.