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Investigators reported in 1993 that the progressive course of retinal degeneration, as assessed by the electroretinogram (ERG), was slower on average among adults with retinitis pigmentosa taking 15,000 international units of vitamin A palmitate daily versus those not on this dose. Participants included in this well-designed, NEI-supported clinical trial had typical retinitis pigmentosa in which affected individuals have comparable loss of rod and cone function or profound loss of rod function with remaining cone function. Findings from this trial led to the recommendation that most adults with the common, typical forms of retinitis pigmentosa should consider taking a supplement of 15,000 international units of vitamin A palmitate daily under the supervision of their doctor. NEI continues to support this recommendation.
A recent publication by Radu et al. reported on experiments involving high dose vitamin A supplementation in albino and pigmented mouse models of one atypical form of inherited retinal degeneration. They reported that such supplementation accelerated the accumulation of a pigment called lipofuscin in the supporting layer of cells beneath the retinas of both albino and pigmented mouse models. Anatomical signs of retinal degeneration were found in the albino mouse model, but not in the pigmented mouse model. The authors did not find ERG changes in either mouse model. These specific models of degeneration were caused by a knockout mutation in the mouse abca4 gene.
The genetically-engineered mice studied by Radu et al. provide models of atypical forms of human retinal degenerations, particularly forms of cone-rod dystrophy and Stargardt macular degeneration in which mutations occur in the ABCA4 gene. However, individuals with these atypical retinal degenerations did not participate in the clinical trial of Vitamin A discussed above, and no treatment recommendations were made for such individuals. Thus, the report by Radu et al. is not directly relevant to the recommendations from that clinical trial which again pertained only to individuals with the typical forms of retinitis pigmentosa. Furthermore, at present there is no compelling public health rationale for individuals with the typical forms of retinitis pigmentosa to be screened for mutations in the ABCA4 gene.