Counseling in medical genetics / Sheldon Reed.

  • Sheldon Clark Reed
Date:
[1980]
Catalogue details

Licence: Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0)

Credit: Counseling in medical genetics / Sheldon Reed. Source: Wellcome Collection.

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    The Physician Discovers the Chromosomes / 41 genetic counseling, which is that it is best to tell the truth and that the truth does not hurt as much if told in a sympathetic and compassionate way. It takes a lot out of the counselor, as it is stressful to him to convey bad news, but it is of benefit to the parents and the child in the long run. As a general rule, nothing good comes from concealing information. For a more detailed description of the subject of sex chromosome aneuploidy, the reader is referred to the book by Robinson et al [1979] sponsored by The National Foundation — March of Dimes. The summary indicates that about 2-1 newborns out of every 1,000 have a sex chromosome anomaly. Consequently, there should be about eight million people in the world with a sex chromosome aneuploidy. This vast number of persons with a gross sex-chromosome defect is greater than the total population of many individual states and countries. It is to be hoped that every physician who examines children will use the book in order to help obtain a feeling for the diagnosis of the child with a chromosome anomaly in order that a chromosome study will be initiated for those affected. Autosomal Chromosome Anomalies (Aneuploidy) There is, of course, one pair of sex chromosomes in each normal cell of a per¬ son and 22 pairs of autosomal chromosomes. It is therefore of interest that over half of the viable chromosomal anomalies are those of the sex chromosomes, and they total more affected persons than all those with chromosomal defects for the other 22 pairs. Part of the reason for this striking phenomenon is that the individ¬ uals with sex chromosome aberrations are usually viable, not only at birth but as adults. This is primarily because we have a dosage compensation effect, known as the Mary Lyon effect, such that only one of the two X chromosomes in females is active in the physiology of each cell as is the case, of course, for males who have only one X chromosome in each cell. In normal females the second X chrom¬ osome becomes inactive and lodges on the nuclear membrane where it is identified as the Barr body. This process allows greater latitude in the number of sex chrom¬ osomes possible in the cells (with consequent viability of the person) than is the case for any of the other pairs of chromosomes. It is thought about 10% of all fertilized eggs have a chromosome abnormality, but less than 1% of newborns are so affected. Many of the chromosomal anomal¬ ies are lost as spontaneous abortions and presumably are the cause of over half of all of such abortions. Kajii et al [1973] looked for trisomies in abortion material and found at least one case for each of 17 of the 22 autosomes. They did not find trisomies for chromosome numbers 1, 5, 12, 17, and 19. No doubt these latter chromosomes would have been found as trisomies also, if the sample of abortuses had been large enough. A most valuable and recent study is that of Hassold et al [1978] of the cyto¬ genetic causes of the spontaneous abortions at the Kapiolani Hospital (Honolulu) between April, 1976, and the end of March, 1977. There were 234 successful
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