Clinical genetics / edited by Arnold Sorsby.

Date:
1953
Catalogue details

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

Credit: Clinical genetics / edited by Arnold Sorsby. Source: Wellcome Collection.

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    THE DETECTION OF THE GENETIC CARRIERS OF INHERITED DISEASE In addition to the diseases included in the Table, it should be pointed out that there are a number of dominant genes in man which are so uncommon that individuals certainly or probably homozygous for the gene in question are very rare indeed. However, such homozygous individuals when they do occur may show a marked accentuation of the effects of the dominant gene, which must then be regarded as an incomplete dominant with the heterozygotes carriers for a much more serious genetic disability. Included in this category may be brachyphalangy (Möhr and Wriedt, 1919), hereditary sebaceous cysts (Munro, 1937), hereditary haemorrhagic telangiectasia (Snyder and Doan, 1944), and the Ehlers-Danlos syndrome (Johnson and Falls, 1949). Recognition of carriers through linkage systems As an alternative to the clinical approach to the detection of genetic carriers, it has been suggested that where the gene responsible for a pathological condition is linked to one producing a harmless trait (for example, a serological char¬ acteristic), one could use the latt^- gene to tag the former. While theoretically this is a feasible method for the detection of carriers, in actual practice many serious difficulties arise (Neel, 1949). The linkage between the marker and the marked gene should be close (within 5 units), and the marker gene to be of maxi¬ mum usefulness should approximate a 50 per cent frequency and be distinguishable in the homozygous and heterozygous conditions. However, since a given pheno- type may be inherited in several different ways, it will be difficult, unless an extensive pedigree is available, to determine the appropriateness of utihzing a particular marker gene. These facts combine to suggest that a very extensive knowledge of human genetics will be necessary before the linkage approach can be of significant practical value. SELECTED BIBLIOGRAPHY Levit, S. G. (1936). J. Genet., 33, 411. Muller, H. J. (1950). Amer. J. Human Genet., 2, 111. Neel, J. V. (1947). Medicine, 26, 115. — (1949). Amer. J. Human Genet., 1, 19. 34