140 CARNEGIE INSTITUTION OF WASHINGTON. 



(4) Dent in forehead. — A fragment of a family history' of a depression 

 in the median frontal region of the cranium led to a publication 

 (Journal of Heredity, April 1915) in which it was pointed out that the 

 trait was inherited as a dominant. 



(5) Huntington's chorea. — This disease, usually regarded as a '' neuro- 

 pathic entity," is defined by the following traits: (1) persistent tremors 

 of the head, appendages, and trunk; (2) the onset of such tremors in 

 middle or late life; (3) the progressive nature of the tremors; and (4) 

 progressive mental deterioration. These characters are frequently 

 found together; is their association a necessar\^ one? 



A study of four family complexes in eastern Long Island, south- 

 western Connecticut, south-central Connecticut, and eastern Massa- 

 chusetts which show nearly 1,000 cases of Huntington's chorea yields 

 the remarkable result that practically all can be traced back to some 

 half-dozen individuals, including three (probable) brothers who 

 migrated to America during the seventeenth century. But numerous 

 ^'biotypes" with specific and differential hereditary behavior have 

 already appeared. Thus, there is a biotype in which the tremors 

 are absent, but mental deterioration is present; a biotype in which the 

 tremors are not accompanied by mental deterioration; a biotype in 

 which the chorea does not progress; and a biotype in which the onset 

 of the choreic movements is in early life. In general, the symptoma- 

 tology of chronic chorea is dissimilar in different strains of families. 

 The age of onset, the degree of muscular involvement, the extent of 

 mental deterioration — all show family differences and enable us to 

 recognize various species, or biotypes, of the disease. These biotypes 

 are less striking than they would be were it not for the extensive h3'brid- 

 ization that is taking place between biotypes in random human 

 matings. The data for the study were collected by Elizabeth B. 

 Muncey, M. D., of the Eugenics Record Office. 



The method of inheritance of some of the elements of Huntington's 

 chorea has been worked out. In general, the choreic movements 

 never skip a generation and in other respects show themselves clearly 

 to be a dominant trait. The mental disorder is usually of the hyper- 

 kinetic or manic type, and this also shows itself as a dominant. The 

 age of onset apparently tends to diminish in successive generations, 

 "law of anticipation," but this is partly, if not wholly, illusory and is 

 due to the fact that in comparing the age of onset in grandfathers 

 with that in grandchildren we are not comparing on the same basis, 

 for the grandparents are a selected lot (selected on the basis of late 

 onset — at least late enough for them to become parents), while grand- 

 children include those in whom the onset is so early in life that they will 

 never marr^^ If instead of comparing the average age of onset in 

 successive generations, one compares the age of onset in a number of 

 choreic parents, their parents, and their grandparents, then the evi- 

 dence for anticipation vanishes. Eight such series give for average 



