Allele-specific knockdown of the SPTLC1 A339T mutation in hereditary sensory and autonomic neuropathy type 1 using custom-designed siRNAs

Topic:

Translational Research

Poster Number: P385

Author(s):

Natalie Yaeger, Department of Neurology, Johns Hopkins School of Medicine, Prerna Kalra, PhD, Johns Hopkins University, Kenneth Gable, Uniformed Services University of Health Sciences, Abby Tadenev, PhD, Rare Disease Translational Center, The Jackson Laboratory, Robert Burgess, PhD, Rare Disease Translational Center, The Jackson Laboratory, A. Reghan Foley, MD, MD(Res), National Institute of Neurological Disease and Stroke, Carsten G Bönnemann, National Institute of Neurological Disorders and Stroke, Teresa M. Dunn, PhD, Uniformed Services University of Health Sciences, Payam Mohassel, [email protected], Johns Hopkins University

Hereditary sensory and autonomic neuropathy type 1 (HSAN1) is a dominantly inherited peripheral neuropathy caused by heterozygous mutations in components of the serine palmitoyltransferase (SPT) enzyme complex. HSAN1 mutations are typically missense variants that alter the substrate selectivity of the enzyme to include L-alanine, or glycine in addition to the standard L-serine. L-alanine and glycine lack a critical hydroxyl group leading to the formation of 1-deoxysphingolipids (deoxySLs), which accumulate in the cell and cause toxicity. In this study, we report a novel variant in SPTLC1 that causes HSAN1 with expected sensory predominant clinical features and associated increase in deoxySLs in serum and patient derived fibroblasts. Using the patient derived fibroblasts, we tested custom-designed siRNAs with strategically placed sequence mismatches that target the mutant transcript for degradation while leaving the wildtype allele intact. Our ongoing in vitro studies will test the effectiveness of these siRNAs in correcting the SPT enzyme substrate specificity. In parallel, we created a novel knock-in mouse model of the disease with the Sptlc1A339T variant. We characterize and analyze the phenotypic and biochemical effects of the A339T mutation on SPT activity. Our preliminary studies in the Sptlc1A339T heterozygous mice show mild behavioral abnormalities consistent with a sensory predominant neuropathy at >70 weeks with trends of higher mechanical thresholds (von Frey) and delayed thermal plantar responses. Grip strength was not altered, and electrophysiologic studies were not different between mutant and control mice. Sptlc1A339T heterozygous mice also show the expected increase of 1-deoxysphingolipids throughout various tissues including the brain, spinal cord, the sciatic nerve, and serum. Future studies will focus on histopathologic characterization of the Sptlc1A339T mouse model including assessment of epidermal nerve fiber layer density, better characterization of age of disease onset in younger animals, and ultimately using our allele-specific siRNA as an in vivo therapeutic strategy.