Familial Creutzfeldt-Jakob disease in Chile.

Of the 87 cases of Creutzfeldt-Jakob disease (CJD) ascertained in Chile since 1931, 39 are familial accounting for 45% of all cases, and 25% of the 51 definite cases. There are 11 affected families with an average of 3.5 affected members per family, and a rate of occurrence consistent with autosomal dominant transmission. There is no evidence for maternal lineage, and age at death is not significantly different from that of sporadic cases. About half of the cases died around the same age, suggesting some form of vertical transmission. Three pairs of affected members in 3 different families died at the same time, possibly indicating common exposure to CJD agent. The study of absolute death intervals and temporal and spatial separations between affected members suggests minimum incubation periods ranging from 2 to 37 years, assuming case-to-case transmission. CJD occurring in a woman related by marriage to one of the affected families strongly argues for horizontal transmission. The high proportion of familial CJD observed in Chile is probably the result of both a genetically determined susceptibility to the CJD virus, and a high degree of case ascertainment. However, the present study leaves unanswered the mode of transmission of the agent within the affected families.