RHEUMATIC FEVER AS A FAMILIAL DISEASE. ENVIRONMENT, COMMUNICABILITY AND HEREDITY IN THEIR RELATION TO THE OBSERVED FAMILIAL INCIDENCE OF THE DISEASE 12

Abstract

The material selected for study comprised 112 rheumatic families from the children''s cardiac clinic. Selection was based solely on residence in the lower and upper west and east sides of New York City. These families, comprising 458 children over 3 yrs. of age, equally divided as to sex, were under observation from 3 to 18 yrs., an average of 9 yrs. These subjects were under close supervision; a record was kept of the onset and termination of every illness of each member of the household. The environmental conditions in the homes were noted. The incidence of rheumatic siblings in 1/3 of the families who lived under relatively favorable environmental conditions was 53%; for the remaining 2/3 where the environmental conditions were unfavorable, 46%. The incidence of rheumatic fever following "active exposure" (to an active case of rheumatic fever), and "inactive exposure" (to a quiescent case of rheumatic fever) was comparable. Intimate contact ("familial exposure") and causal contact ("extra-familial exposure") were equally effective. These observations are consistent with the concept that the etiological agent may be widespread in this geographical environment. A direct relation was observed between the incidence of rheumatic siblings and parental rheumatism. The markedly lower incidence among fraternal twins as compared with identical twins also suggested a genetic background. The assumption of a single recessive gene responsible for susceptibility to rheumatic fever is sufficient to account for the familial incidence observed. Among 58 families of negative parents the observed and expected incidence was 94 and 88 respectively. Close agreement between observation and prediction was also obtained for families when father or mother were positive. The variation was in all groups under 1.1 [sigma]. Special tests resulted in the exclusion of dominance, involving one or more genes, and recessiveness, involving 2 or more genes, as well as sex linkage, as possible interpretations for the familial incidence. An inherited susceptibility may not always yield rheumatic fever. In a test series, the penetrance among susceptibles was 82 to 86%. The authors conclude that hereditary susceptibility would seem to determine the familial incidence of rheumatic fever, but may not necessarily be the sole condition essential for the development of the disease.