DISCUSSION of the etiology of multiple sclerosis has repeatedly aroused the speculation that genetic, constitutional factors might be involved. Considerable interest has therefore been accorded to reports of the occurrence of the disease in several members of the same family. As long as these reports are confined to the histories of a number of "familial" cases, their value as proof is extremely limited. This applies even when the author gives the percentage number of "familial" cases in a certain group of patients. If a satisfactory genetic study of the disease is to be made, it is necessary to investigate its incidence among the relatives of the affected persons (the probands) or to make studies of twins. Two investigations of the former kind have been made (Curtius and Speer,1 1937; Pratt, Compston, and McAlpine2 (1951), and one of the latter (Thums,3 1939).
Curtius and Speer1 made a