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R.C. Caruso, Z. Quezado, S.W. Levin, K.H. Fischbeck, A.L. Gropman, S. Hofmann, N. Patronas, K. Wisniewski, Z. Zhang, A.B. Mukherjee; Serial electrophysiological measurements of of visual function in infantile neuronal lipofuscinosis. . Invest. Ophthalmol. Vis. Sci. 2004;45(13):5141.
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Purpose: The aim of this study was to assess abnormalities in the electroretinogram (ERG) and visual evoked potential (VEP) in infantile neuronal ceroid lipofuscinosis (INCL) (OMIM # 256730) and their rate of change during the course of a treatment trial. INCL is a neurodegenerative disease caused by mutations in the gene encoding palmitoyl–protein thioesterase (PPT), which leads to retinal degeneration and optic atrophy. Methods: Two girls with inactivating mutations in the PPT1 gene were included in a pilot clinical study conducted to determine the effect of cysteamine bitartrate (Cystagon) on INCL. Patient 1 was recorded on 5 occasions between the ages of 1.5 and 4.1 years. Patient 2 was recorded on 4 occasions between the ages of 2.1 and 3.8 years. ERGs and VEPs elicited by Ganzfeld flash stimuli were recorded according to ISCEV standards; ERGs were recorded under propofol anesthesia. Response amplitude vs. time functions were fitted with an exponential model to estimate the half–life of each response. Results: ERG responses showed a more severe b–wave reduction than a–wave reduction; this electronegative configuration implies an abnormality at, or proximal to, the photoreceptor–bipolar synapse. Rod–mediated b–waves were more compromised than cone–mediated b–waves. ERGs elicited by 150 ms stimuli showed that b–waves were more affected than d–waves. After age 2, the amplitude of all responses declined considerably with time, with a half–life of approximately 1 year (1.08 ± 0.22 years). A correlation with progressive abnormalities in retinal pigmentation was observed. The P2 peak of the flash VEP showed normal implicit time but reduced amplitude. After age 2, P2 amplitude declined even more rapidly than ERG amplitude with time, with a shorter half–life (0.41 ± 0.01 years). A correlation with progressive optic disc pallor was observed. Conclusion: INCL caused a rapidly progressive deterioration of retinal and optic nerve function. Our data did not allow us to determine if the spontaneous course of the disease would have been even more rapid than the one observed in this treatment trial. However, they emphasized the fact that a therapeutic intervention for INCL should be instituted very early in life to preserve retinal neuronal function.
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