1998 Heredity of Eye Defects - Howe Jour. A.M.A.
June 27, 1918
Abstract of Discussion
Dr. Horatio H. Newman, University of Chicago: This occasion gives me great opportunity of expressing an idea that has long been at the back of my mind, that cooperation between the professional ophthalmologist and the professional geneticist might lead to far reaching results in both fields. This idea was suggested to me some years ago by a piece of genetic work which fell into my hands quite accidentally. While instructing a class in genetics at the University of Texas I dealt with night blindness as an example of one type of heredity. I made a statement that night blindness was a partially sex-limited character, appearing in every generation, but largely restricted to males.
After the class a young woman said that there was something like hereditary night-blindness in her family, but it did not follow the law stated. I found that there was quite a large family connection who were night-blind and that the defect was inherited as a sex-linked character. This led me to work out the data of optic defects for five generations of this family, which was published some years later in the [italics]British Journal of Genetics[end italics]. The point I wish to bring out is the great difficulty that I had as a geneticist in handling that data. If I had had the cooperation of an ophthalmologist the task would have been greatly simplified. As it was I had to depend on advice kindly offered by Nettleship, advice which though meager was of the utmost value.
That, then, will bring out my point, that it would be a very valuable thing if the ophthalmologists and the geneticists could actually get together in working out some of these problems that concern these two fields.
I think I am safe in saying that nothing equals the data of ophthalmology for the study of human heredity. And particularly is that true in connection with sex-limited and sex-linked heredity. We have founding our experiments on a number of the lower animals, that some characters are inherited in a particular way in a sex-limited and others in a sex-linked fashion. A sex-linked character is one that is limited to the male sex, while a sex-linked character may, under certain conditions, appear in females also. The mechanism of sex-linked heredity has been worked out and may be explained in a diagram (explanation of diagram omitted). This illustrates but one of the many interesting phases of the genetics of optic defects.
Dr. F. Park Lewis, Buffalo: Dr. Howe's paper naturally revolves itself into three distinct parts: that dealing with the mendelian law, which is a science in itself; that dealing with its application economically and socially, and the question, finally, as to what shall be done about it.
The question of the mendelian law is one of the most interesting, probably, of all topics that has come before the scientific world in a generation. Our knowledge of it dates from the beginning of the present twentieth century, although Mendel wrote in 1881 an essay in which he demonstrated on peas the application of his law. This essay was buried in the archives of a scientific society for all the years intervening between that time and 1900, when Bateson and others, working along the same lines, brought it to the surface and found that this Austrian monk had hit on a law of heredity the importance of which can be scarcely overestimated.
Its application in ophthalmology to the development of the eye is particularly interesting, but I shall have to speak only on the economic side of it, which seems of great importance as a war measure.
The most important product now which we are raising - and we are now considering the conservation of our products - is that of our children. What is done in regard to the development of our children during the next twenty years connotes what kind of population we shall have twenty years hence. During the last three decades there has been a very rapid decrease in the birth rate among all English speaking people, as there has been among the French, until at the beginning of the war, in 1914, the proportion had been reduced from thirty-five in a thousand in England, to about twenty. The large number of males who are taken out of active service and sent abroad will still further decrease our birth rate during these years of war.
The classes of people whose birth rate continues high as a rule are those who live under the most unsanitary conditions. In the Polish population, where it is very crowded, the average number of members in a family is eight. In what we call the better classes of people, those who are more intelligent, the average number of children in a family is but three. It has been found that where people live in four room tenement houses, the number of children who live is about thirty-five in a thousand. Where they live in three room tenement houses the proportion is about thirty in a thousand. Where they live in one room tenement houses, the number who live is still further reduced. So that the housing problem means that we are losing the productive element in our population in very large proportion, just to the degree that we decrease the sanitary conditions under which they live.
Moreover, where defects of any kind exist, defects in vision or other characteristics, the grouping of people together is very apt to make those whoare sufficiently closely related to have the same traits, and the possibility of perpetuating those traits, brought together so that they are apt to marry. It happens that during the last twenty-five years I have been connected with the School for the Blind, and I have seen during those years the effect of the perpetuation of the defects of blindness in the most remarkable degree. Four generations ago two congenitally blind people married. The progeny, the result of that marriage, have been coming back to the school during those twenty-five years, until we have now had from one family, seventeen, and from another family of cousins, seventeen. Without going into details of the economics involved, I may say that single marriage has cost the state of New York more than $50,000 for the education and maintenance of all these blind people.
I was interested in the case in the prevention of ohpthalmia neonatorium, because of the multitude of cases that I found in the School for the Blind who were blind as the result of birth infection. The number of children that are blind as the result of congenital atrophy was greater, and always has been greater than that resulting from ophthalmia neonatorium.
Dr. Clarence Loeb, Chicago: Assuming the correctness of the mendelian theory, we must remember that it was worked out with plants and animals, where there is more than one offspring of a single mating. In man, however, a single mating, as a rule, results in one offspring, seldom two and very infrequently three or more. I do not see that it necessarily follows that the facts in the former case, that is, where there are more than one offspring at a birth, are true in a case in which there is only one. But granting that the facts will be the same, the theory further demands that two of the same generation must mate, which never takes place in man under present circumstances. Formerly, and in the far dim past, brothers and sisters would mate, but at the present time this never takes place.
How can we assume that the mating of two strains, as in the case of the marriage of two blind, unrelated people, will have the effect as the joining of two strains from the same source? As a matter of fact, the histories of the cases in which two blind parents, whether related or not, marry, show that the percentage of their children was no greater than when one blind and one seeing person married. Furthermore, the mating of the red sweet pea for example, with the white sweet pea, is the mating of the normal characteristics, while the mating of a blind with a seeing person, is the mating of a normal with a pathologic condition. How do we know that the theory will work out under those circumstances? The histories of these cases show that it does not, as the percentage of children affected, whether there was more than one child from one family or not, ranges anywhere from 100 per cent to no per cent; that is, all the children, to none of the children. There is no definite rule that can be followed. Take up a history and you are as likely to find all the children of such a marriage become blind as only one or none.