969. Development of Non-Invasive Imaging Strategies to Assess the Impact of Gene Therapy: Phenotypic Assessment of the Neurodegenerative CNS Disorder Late Infantile Neuronal Ceroid Lipofuscinosis Using Magnetic Resonance Spectroscopy
Authors: Neil R. Hackett, Dolan Sondhi, Stephen M. Kaminsky, Stefan Worgall, Lisa A. Arkin, Charleen A. Hollmann, Dikoma C. Shungu, Xiangling Mao, Jonathan P. Dyke, Linda Heier, Mark Souweidane, Michael Kaplitt, Ronald G. Crystal
Journal: Molecular Therapy (2005)

Several animal models of neurodegenerative lysosomal storage disease have been successfully treated by intracranial gene transfer. Among the most challenging aspects of moving these strategies to the clinic is to identify objective outcome parameters to measure the success of gene therapy. Classical phenotyping with measurement of neurological functional parameters and/or survival will take years of observation, it is not ethical to obtain brain biopsies following treatment for histological analysis, and there are limited numbers of children with these disorders to develop comparable treated and control groups. We have commenced a program of AAV-mediated gene therapy for the CNS manifestations of late infantile neuronal ceroid lipofuscinosis (LINCL), a fatal childhood neurodegenerative lysosomal storage disease with no known therapy resulting from mutations in the CLN2 gene and a deficiency of the lysosomal protease tripeptidyl peptidase I. As part of this program, we have assessed whether magnetic resonance spectroscopy (MRS) is sufficiently sensitive and reproducible to assess the impact of intracranial gene transfer in humans with neurodegenerative diseases. To date, 8 children with LINCL (ages 6.25 to 13.75 yr old) have been successfully scanned and four of these children were scanned twice at intervals from 17 to 126 days. MRS scans were performed in a 3.0 Tesla GE Signa LX scanner generating 1H images of 4 brain sections of 15 mm thickness separated by 3.5 mm. Strong MRS signals from pericranial lipid resonances and water were suppressed. The raw data were processed to give the concentrations of four metabolites, lactate, choline, creatine (Cr) and N-acetylacetate (NAA) in multiple voxels (8 |[times]| 8 |[times]| 15 mm). Analysis was confined to those regions of the cortex that were accessible for surgical administration of gene transfer vectors. Initially we assessed the NAA/Cr ratio, an index of neuronal function. The NAA/Cr ratio in the target area was 1.60 |[plusmn]| 0.16 in the youngest LINCL patient and 0.58 |[plusmn]|0.18 in the oldest. The NAA/Cr ratio decreased with a slope of |[minus]|0.10/yr (r2=0.43; 95% confidence intervals |[minus]|0.186 to |[minus]|0.019/yr). The difference in NAA/Cr ratio between the first and second scans from the same subjects was |[minus]|0.52|[plusmn]|0.53/yr suggesting that the NAA/Cr ratio is poorly reproducible in duplicate scans of similar brains. Assuming a low estimate of the overall coefficient of variation in measurement of NAA/Cr ratio of 20% (from spatial variability and variability among scans), we calculated that if the NAA/Cr ratio was stabilized by gene therapy in one third of the voxels in the target area, this would be evident by statistical analysis at 18 months post-surgery. We conclude that MRS may provide objective evidence of local changes in metabolite concentration following gene transfer, but to accomplish this will require repeat scans over greater than 1 yr following gene transfer.