GM2A and GM2 gangliosidosis: When we first published on such a patient in 1983 we called the disease GM2 gangliosidosis Hex AmB variant to indicate that the α‐chain of Hex A has a mutation missed by the heat denaturation method.8 Patients who clinically resemble GM2 gangliosidosis but who have normal Hex A and B activity may have a deficiency of GM2 activator protein required for bringing GM2 ganglioside together with Hex A. The diagnosis was made in six patients by looking at the increase in GM2 ganglioside in cerebrospinal fluid using a method developed in this laboratory.9