Genetics in ophthalmology / Arnold Sorsby.

  • Sorsby, Arnold, 1900-1980.
Date:
1951
Catalogue details

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

Credit: Genetics in ophthalmology / Arnold Sorsby. Source: Wellcome Collection.

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    CLINICAL VARIETIES OF GENETIC DISEASE ABIOTROPHIES Abiotrophie lesions have not been studied to any extent in animal genetics. Abiotrophy is, however, an undoubted clinical phenomenon: a classical example is retinitis pigmentosa. Here the children are born apparently normal and retain normal vision until the onset of the genetically determined disturbance of the fundus. Abiotrophies affecting children and young adults have been recognized for many years. It is only lately that there has been any clear appreciation of the fact that genetically determined anomalies may not become manifest until well in middle life, or even possibly in old age. In general medicine Huntington's chorea stands out as an important example of an abiotrophic process frequently coming on in middle life. The blood dyscrasias (as distinct from Rhesus factor disturbances and haemophilia which are congenital anomalies) are less clearly recognized as genetic anomahes of late onset. In ophthalmology there is some evidence that maôular dystrophy may develop in middle life and later, and there is proof of a widespread chorioretinal dystrophy which begins as a macular lesion at about the age of 40 years and leads to total or subtotal blindness by the age of 70 years. The conception of abiotrophy implies not only hereditary transmission of a disease process, which is sometimes latent for many years, but also carries the implication that the hereditary disturbance becomes manifest in a tissue that had developed normally and had functioned normally for some years. Evidence that the tissue was in fact normal is unlikely to be available from human observations. An excised eye showing retinitis pigmentosa gives no information as to the state of the retina before the affection developed. An increasing number of abiotrophic processes are being isolated. Outstanding amongst these are the corneal dystrophies, the macular dystrophies, Leber's optic atrophy, and the group of affections known as retinitis pigmentosa. It is also likely that many cases of optic atrophy, and some, if not the bulk, of glaucoma and senile cataract and ill-differentiated fundus lesions are genetically determined abiotrophies. Clinically four features are generally ascribed to the abiotrophies: Familial stamp Within the same family there is said to be a striking similarity in onset, clinical course, and appearances of the particular affection, such as say retinitis pigmentosa or macular dystrophy. This is true to a large extent, but is no absolute rule. Affected members of a family share not only the same pathogenic gene, but to a large extent a similar total genetic constitution, and to a certain extent also a similar environment. These are all factors that tend to produce uniformity and similarity in clinical manifestations within a particular group, and help to explain variations as between different family groups. Individual variations within a group, however, do occur not infrequently, as different members do not, of course, have an identical total genetic constitution or environment. In assessing dis¬ similarity as between different members of a group, it must be borne in mind that the abiotrophies are generally progressive and strictly comparable stages are not frequently seen within a sibship. 51 mmetry Symmetry as to site, general appearance and effects is frequently present in 56 »