Huntington's chorea, a constitutional affection in the strictest sense, occurring on a hereditary basis, forms a group apart from and apparently entirely independent of the other constitutional disorders thus far considered. Arrests of development, epilepsy, dementia praecox, paranoia, manic-depressive psychoses, involutional melancholia, hysteria, and allied conditions often enough present a history of similar heredity, but at least as often, if not more so, they present a history of dissimilar heredity, so that we find instances of two or more of them existing in the same family. For this reason it is generally held that these conditions, though forming clinically fairly distinct entities, are nevertheless in some manner related to each other. The case is different with Huntington's chorea. In all cases in which a complete family history has been secured the heredity which was found has been similar. Instances of other neuropathic conditions are, indeed, occasionally observed in the families of patients suffering from Huntington's chorea, but they are relatively so infrequent as to be readily accounted for as coincidences essentially without relationship to the chorea itself.
Another reason for assigning to Huntington's chorea an independent position among the constitutional disorders is the special manner in which it is transmitted by heredity. Such evidence as is available indicates that the neuropathic conditions enumerated above are for the most part transmitted in the manner of Mendelian re.cessives. (See Chapter I, Part I of this Manual.) Theoretically, then, the development of a case requires a convergent heredity, and in practice such heredity is very frequently found where a complete family history is available; furthermore, the hypothesis of recessiveness offers an explanation of the frequently observed fact of atavistic heredity in connection with cases of these conditions. Pedigrees in cases of Huntington's chorea practically never show either convergent or atavistic heredity; even in families heavily charged with this condition an individual who happens to be free from it is also free from the risk of transmitting it to his offspring; in other words this disease does not skip a generation as other neuropathic conditions frequently do.
Thus Huntington's chorea, considered as a biologic trait, behaves, unlike the large general group of other neuropathic conditions, not as a Mendelian recessive, but as a dominant in relation to the normal condition.1
The disease is comparatively rare, yet most institutions for the insane can show one or more cases. Both sexes are about equally affected. The age of onset in typical cases is between thirty-five and fifty. The development is gradual, beginning with slight irregular movements of the face and upper extremities which extend slowly over the rest of the body, at the same time becoming more severe; the movements are almost constant, ceasing only during sleep; the patient's speech becomes affected eventually, growing indistinct and unintelligible. There are no disturbances of sensation. Mental symptoms appear in almost every case sooner or later: "a weakness of judgment and initiative, absent-mindedness, general dissatisfaction with surroundings, a growing selfishness and irritability are among the earliest symptoms observed."2 The fully developed mental picture is characterised by marked irritability, ideas of persecution, and a slow but progressive deterioration; the latter consists mainly in a "disinclination toward mental exertion, which is so pronounced that the examination becomes very difficult; in the marked cases it interferes even with such simple reactions as stating whether it is summer or winter, and seems to give rise to the fact that the patient does not respond at all, or responds in a perseveratory manner; in the milder cases it shows itself in calculation, in giving time relations, and in giving the substance of a simple story read to them, leading to the excuse that the memory is bad, that they are unable to tell it, etc.; whereas, on the other hand, in the orientation, even in the worst cases, there is remarkably little interference; the memory of actual facts, if sufficiently insisted upon, is found to be quite good." 1 In the original description of the disease Huntington mentioned marked suicidal tendency as being very common,2 and this observation has been corroborated by most of the later writers.
1C. B. Davenport and E. B. Muncey. Huntington's Chorea in Relation to Heredity and Eugenics. Amer. Jour, of Insanity, Oct., 1916. (Bulletin No. 17, Eugenics Record Office, Cold Spring Harbor, N. Y.)
2 A. S. Hamilton. A Report of Twenty-seven Cases of Chronic Progressive Chorea. Amer. Journ. of Insanity, Jan., 1908.
Huntington's chorea is a chronic, slowly progressive, incurable affection. It cannot be said to be in itself fatal, death usually occurring at the end of many years from some intercurrent disease.
While the majority of cases correspond fairly closely to the above description, more or less marked variations from the most common type are frequently seen. The onset may occur at an early age, even in childhood or in infancy, or later than usual, in advanced senility; the symptoms may be mild, consisting of slight movements, limited in distribution, and unaccompanied by any mental disorder; or the mental deterioration may be particularly severe and set in long before the choreic movements develop.3
1 W. G. Ryon. A Study of the Deterioration Accompanying Huntington's Chorea. N. Y. State Hosp. Bulletin, Feb., 1913.
2 George Huntington. On Chorea. The Med. and Surg. Reporter, Apr. 13, 1872.
3 C. B. Davenport. Huntington's Chorea in Relation to Heredity and Eugenics. Proc. of the National Academy of Sciences, Vol. I, p. 283, May, 1915.
The anatomical changes found post mortem consist mainly of brain atrophy, shrinkage of cortical cells with dilatation of peri-cellular spaces, and occasionally internal hemorrhagic pachymeningitis.