Visual functions in Tay Sachs diseased patients following enzyme replacement therapy

Three patients with Tay Sachs disease diagnosed on clinical as well as on enzymatic findings were followed during a trial of enzyme replacement treatment. Purified hexosaminidase A enzyme extracted from human placentae was directly injected intraventricularly or into the spinal canal of these patients. The electrophysiological investigation of the visual system was done utilizing standard techniques. The visual evoked potentials (VEP) were extinguished in all the cases. The electroretinograms (ERG) had normal patterns but abnormally large amplitudes. The ERG amplitudes were found to increase with the progression of the disease forming a part of a continuum rather than different retinal functional expressions. No influence of the treatment on these electrophysiological visual parameters were observed. The possible neuronal mechanism responsible to this hypernormal ERG amplitude and the diagnostic value of repeated examinations are discussed.