Fig. 24
Radiograph (Courtesy of Dr. W. B. Helm) showing a partial syndactyly in each hand of an individual. Some degree of webbing between the more distal portions of the affected parts is usual.
Fig. 25
Pedigree of a family with presenile cataract (black symbols); numbers in circles indicate unaffected individuals (after Davenport).
Other Defects Inherited as Dominants.—Not to go into details other defects which behave as dominants or modified dominants in human inheritance may be mentioned. The following list is not complete and it must be understood that in some cases the statistics are insufficient to justify us in making anything but a tentative decision. We may thus enumerate as dominant over normality: Achondroplasy (abnormally short limbs with normal head and body); Keratosis (thickening of epidermis); Epidermolysis (excessive formation of blisters); Hypotrichosis (hairless, toothless condition); Diabetes insipidus; Diabetes mellitus; ordinary (not Gower’s) muscular atrophy; Glaucoma (internal swelling and pressure of eye-ball); displaced lens; Coloboma (open suture in iris); spottedness of hair-coat; and corneal opacity.
As a final illustration of a serious malady in man which acts as a dominant in inheritance, let us take Huntington’s chorea. Ordinary chorea, or St. Vitus’ dance, a disorder characterized by involuntary muscular movements, is commonly though not always confined to children and usually ends in recovery, but Huntington’s chorea appears typically in middle life and is a much more dangerous malady. Fig. 26, [p. 114], represents the family history of one of five cases which have been studied by Doctor Lorenz in the Mendota Hospital for the Insane. All charts which have been platted of this malady show it to be inherited as a dominant. This means that half of the children of an individual who carried the malady in the simplex condition, and all the children of one who carries it in the duplex condition, are probably marked for this terrible end. And the true horror of it can only be appreciated by one who has seen the last stages of the malady. The victim once in its grasp gradually becomes wrecked in mind and body; the muscular twitchings and disorders of movement continually increase and dementia progresses until at last death ensues. Fig. 27, [p. 115], is another chart showing inheritance of Huntington’s chorea. In still a third case at the Mendota Hospital, the gravity of the situation can be appreciated when one realizes that the patient is the father of ten children, ranging in age from one to seventeen and one-half years. The calamitous fact that this disease does not manifest itself usually until middle life makes it likely that these children will all reach maturity, marry and in turn probably produce offspring before the doomed members of the family realize their fate.
