Eight GD patients with intact spleens were treated with 60U/kg (n=4) or 30 U/kg (n=4) biweekly. QCSI results were compared to results in 15 untreated GD patients with a follow-up interval of 1 year extracted from the Dutch Gaucher database. Results: Five taliglucerase treated patients had a decreased Ff (<23%) at baseline (median (n=8): 19%, range 11-35%). Ff significantly increased compared to baseline (p=0.012) and com- pared to untreated patients (p = 0.007) already after 1 year of follow- up with further improvement up to 36 months (median absolute increase at max. follow-up 13.5% (range 5-29%). No difference for the two dose groups was established. Conclusion: Treatment with taliglucerase alfa results in significant increases in bone marrow fat fractions. (1) Zimran A, Brill-Almon E, Chertkoff R, Petakov M, Blanco-Favela F, Terreros ME, et al. Pivotal trial with plant-cell-expressed recombi- nant glucocerebrosidase, taliglucerase alfa, a novel enzyme replace- ment therapy for Gaucher disease. Blood 2011 Sep 6. doi:10.1016/j.ymgme.2011.11.167 Genome-Wide RNAi Screen For Lysosomal Storage Disorders Arash Velayati a , Pinar Tuzmen b , Rajarshi Guha b , Scott Martin b , Ehud Goldin a , Ellen Sidransky a , a Medical Genetics Branch, National Human Genome Research Institute, National Institutes of Health, Bethesda, MD, USA, b RNAi Screening Core Facility, NIH Chemical Genomics Center, National Human Genome Research Institute, National institutes of Health, USA Untangling the web of genes contributing to the phenotypic diversity in monogenic disorders will contribute to our understanding of disease mechanisms, provide insight into complex genetic disorders and lead to new therapeutic options. We performed genome-wide RNAi screening to probe multiple genes in well defined pathways, to assess their effect on function and to identify novel protein interactions for three common lysosomal storage diseases (LSD), Gaucher disease (GD), Fabry disease and Pompe disease. RNAi libraries available from the NIH RNAi screening core facility were printed in 384-well plates and transfected into fibroblast and BE(2)-M17 neuroblastoma cell lines using standard methods. Activity of each selected lysosomal enzyme was assayed in cell lysates 72 hr after transfection using a fluorescent substrate. Standard normalization and data analysis protocols were used for hit selection. Candidate genes identified were confirmed by follow-up screens and further by evaluated to analyze their effect on cell viability, lysosome function and integrity, global gene expression and intracellular transport. The RNAi screening data from distinct LSD were compared to identify shared genes of interest, which may have direct relevance to lysosome biogenesis and function. Specific genes relevant to individual LSD were explored as potential therapeutic targets. The Next, cell based assays using fibroblast lines from patients with GD and other LSD will be utilized to investigate gene function. doi:10.1016/j.ymgme.2011.11.168 Impaired Medullary Hematopoiesis in Murine Mucopolysacchar- idosis Type I Gustavo Viana, Edgar Julian Paredes-Gamero, Ana Maria Martins, Vânia D'Almeida, Universidade Federal de São Paulo (UNIFESP), São Paulo, São Paulo, Brazil Mucopolysaccharidosis type I (MPS I) is an autossomal recessive disease caused by alpha-L-iduronidase deficiency, leading to impaired glycosaminoglycan (GAG) degradation. The subsequent GAG accu- mulation in tissues is responsible for various pathological features like mental retardation, short stature, cardiorespiratory complica- tions, joint stiffness and dysostosis multiplex. Although aberrant bone remodeling and growth plate abnormalities with disorganized trabecular morphology were recently described in MPS I mice, the cellular turnover in bone marrow (BM) remains unknown. Thus, the aim of our study was to analyze murine MPS I BM hematopoiesis. Three-month-old MPS I and wild-type (WT) mice were euthanized and BM cells were extracted from right/anterior femora. The cell pellets were resuspended and analyzed through flow citometry for each subpopulation. Myeloid common progenitors and natural-killer cells were significantly decreased in MPS I compared to WT mice (p<0.01). In addiction, activated B-lymphocytes were also decreased in MPS I group (p<0.05). However, no alterations were found in peripheral blood cells count (hemogram). These results suggest that bone abnormalities found in murine MPS I can impair effective medullary hematopoiesis and possibly justify bone alterations presented by patients and other pathological processes manifested locally and systemically in this disease. Financial support: FAPESP, CNPq, IGEIM and AFIP. doi:10.1016/j.ymgme.2011.11.169 Intracerebroventricular (ICV) Recombinant Human Tripeptidyl Peptidase-1 (rhTPP1) Enzyme Replacement Attenuates Disease Progression in a Canine Model of Late Infantile Neuronal Ceroid Lipofuscinosis (LINCL) Brian Vuillemenot a , Martin Katz b , Joan Coates b , Derek Kennedy a , Camille Flournoy b , Christine Sibigtroth b , Rebecca Whiting b , Randal Reed c , Eric Adams c , Laurie Tsuruda a , Donald Musson a , Charles O'Neill a , a BioMarin Pharmaceutical Inc., Novato, CA, USA, b University of Missouri, Columbia, MO, USA, c Northern Biomedical Research, Inc., Muskegon, MI, USA LINCL is caused by lack of the enzyme TPP1. LINCL patients exhibit accumulation of lysosomal storage in the CNS accompanied by neurodegeneration, loss of function, and death. TPP1-null dachs- hunds recapitulate many symptoms of the human disease. This study was performed to determine the pharmacology of ICV rhTPP1 in this model. An additional objective was to characterize the pharmacoki- netics (PK) and distribution in the CNS. Affected animals (N= 9) and wild-type controls (N=9) received ICV infusions of 4 or 16 mg rhTPP1 or artificial cerebrospinal fluid (CSF) vehicle. rhTPP1 was administered as two or four hour infusions via a catheter implanted in a lateral ventricle. Animals received approximately 20 biweekly doses starting at age 2 months. Serial plasma and CSF samples were collected during and after dose administration to characterize rhTPP1 PK. Elevated CSF concentrations were observed for at least 48 hours after infusion and were approximately 1000-fold higher than plasma levels. Neurological and clinical examinations, electretinography, measurement of pupillary light reflexes and visual evoked potentials, magnetic resonance imaging, and cognitive testing were performed throughout the study to assess disease progression. Necropsy occurred 48 hours after the final dose at approximately 11 months of age. Animals given 4 mg doses of rhTPP1 exhibited improved clinical signs and attenuated functional decline compared to vehicle treated controls. In-life assessments at the 16 mg dose level, as well as analysis of CNS tissues for rhTPP1 concentration, storage material, and markers of neuronal injury, are ongoing. doi:10.1016/j.ymgme.2011.11.170 Abstracts / Molecular Genetics and Metabolism 105 (2012) S15–S69 S63