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(1) Hereditary lesions fall into three groups:—
(a) Malformations: Present at birth.
(b) Abiotrophies: At birth the tissue is fully differentiated but it undergoes degenerative changes at some period in post-natal life.
(c) Phakomatoses: A group possessing features of the two previous groups and some features of neoplasms.
(2) The conception of abiotrophy draws attention to a large group of affections which have a hereditary character and develop in apparently normal tissues, making their appearance in different families at different periods of life. The conception is well established in neurology. Ophthalmology offers numorous examples. A large variety of familial fundus lesions (other than hereditary congenital anomalies), the corneal dystrophies (generally setting in at about puberty), “senile” cataract (occurring with regular frequency in certain families at certain ages), all illustrate the occurrence of familial groups of affections in tissues that show no obvious congenital anomaly, structurally or functionally. Whether this group is called heredo-degenerations or abiotrophies or by some other name is of little significance in comparison with the recognition of the existence of such a clinically distinct group.
(3) The understanding of the nature of these affections is rudimentary. Studies in the mode of inheritance of the different abiotrophies help to explain their distribution, but not their nature, just as the genetics of congenital malformations do not explain the embryological mechanism underlying these defects.
(4) The earlier workers of this branch of genetics were inclined to attribute the degenerative process in post-natal life to a failure inherent in the cell. Present evidence indicates that in the abiotrophies it is the environment of the cells rather than the cells themselves that is at fault. Work along these lines has already led to valuable therapeutic results in affections that were previously regarded as incurable (acholuric familial jaundice; Schüller-Christian syndrome).
(5) The abiotrophies of the retina and choroid are indicated. The solution of the problems they present lies in the study of their general associations. These are discussed.