In 1995, while caring for a 2 year old Iranian child with newly diagnosed Tay-Sachs disease, Richard Proia, Ph.D., (GDDB/NIDDK) was constructing mouse models of Tay-Sachs and Sandhoff disease. Mutual interest led to a collaboration between Dr. Tifft's group and Dr. Proia's group to understand the pathogenesis of disease progression in these uniformly fatal disorders and to explore therapeutic options. The collaborators determined that bone marrow transplantation could double the lifespan of Sandhoff disease mice, not by decreasing the storage of GM2 ganglioside, but by inhibiting activation of macrophage-derived microglial cells leading to neuronal apoptosis. This was the first demonstration that inflammation was pivotal in the pathogenesis of lysosomal storage disorders (LSDs) affecting the central nervous system (CNS), an observation that has been subsequently extended to include many neurodegenerative LSDs. Anti-inflammatory compounds have also improved behavior and lifespan in the Sandhoff mouse, further supporting inflammation as an important contributing factor to neurodegeneration.
In further studies using bone marrow transplantation in combination with substrate inhibition with the glucose analog, miglustat, Dr. Tifft's group showed a synergistic effect on improved behavior and lifespan. This drug has also showed efficacy in a limited number of patients with GM1 gangliosdisosis.
Activation of inflammatory cascades may account for the pathogenesis of many neurodegenerative disorders, including Alzheimer's and Parkinson's diseases and multiple sclerosis (MS). Fingolimod (FTY720), a newly approved drug for the treatment of MS is thought to act through sphingosine-1-phosphate (S1P) and its G protein-coupled receptor S1P1. Using knock-out mice for S1P and its receptors, the Proia laboratory studies sphingosine metabolism and its relation to health and disease. In collaboration with them, the Tifft lab is now breeding S1P and S1P1 conditional knock-out mice to the Sandhoff animals as a genetic proof of concept in mitigation of disease progression in this gangliosidosis model. They are also investigating FTY720 in the Sandhoff mouse as a possible therapeutic agent.
To further investigate the molecular pathogenesis of these devastating disorders, Dr. Tifft's team has generated induced pluripotent stem (iPS) cells from a patient with infantile Sandhoff disease and is using the CRISPR/Cas system to correct the mutation and produce isogenic iPS lines for neuronal differentiation and differential gene expression studies.
GM1 gangliosidosis is a rare disorder caused by the enzyme deficiency of b-galactosidase. The researchers have recruited nearly 20 patients for careful phenotyping and monitoring of disease progression. They developed an MRI severity score that differentiated two discrete groups of patients they call late-infantile and juvenile onset disease. The severity core also correlated with disease progression. In collaboration with Eva Baker, M.D., Ph.D., in the Diagnostic Radiology Department of the NIH Clinical Center, Dr. Tifft's group quantitated brain metabolites N-acetyl aspartate (NAA), choline, and myoinositol using MR spectroscopy. A statistically significant decrease in NAA in several brain regions correlated with loss of motor and language milestones in the patients and was also able to differentiate the late-infantile from juvenile cohorts, making it an excellent non-invasive biomarker for therapeutic trials.
In collaboration with University of Mainz, Germany, skeletal dysplasia expert Jurgen Spranger, M.D., we have evaluated serial skeletal radiographs in a cohort of GM1 patients. Interestingly, the degree and progression of bony pathology appears less related to CNS degeneration than the specific genetic mutation.
Ongoing work in the laboratory focuses on the mechanisms of neurodegeneration and on the identification of biomarkers of disease progression, including ganglioside quantitation and identification of inflammatory markers in cerebrospinal fluid (CSF), and glycan profiling in urine, plasma, and CSF.
As director of the Pediatric Undiagnosed Diseases Program (UDP), Dr. Tifft and her team evaluate patients who have long eluded diagnosis at major academic centers throughout the country. The majority of patients have neurologic, often neurodegenerative, disease as part of their symptomatology. By careful clinical phenotyping and using the latest techniques in next generation sequencing and agnostic screening, the team tries to solve mysterious conditions that may represent very rare presentations of previously described disorders or entirely new disorders. Synergistic with her interest in lysosomal storage disorders (LSDs), Dr. Tifft and her team have developed an agnostic screening assay in UDP patient fibroblasts based on increased size or number of acidic lysosomes or endosomes within the cell to identify individuals with suspected new disorders in vesicular trafficking. Cell lines of many of her LSD patients have served as positive controls in the development of this assay. This information, in combination with clinical phenotyping, will assist in identifying and functionally validating strong candidate genes identified by next generation sequencing. An even greater potential for identifying new diseases is anticipated with the extension of UDP into the Undiagnosed Diseases Network with the addition of 6 additional clinical sites and a coordinating center.
Glycosphigolipid Disorders Laboratory Members
Debra Regier, M.D., Ph.D., Genetics Fellow
Gretchen Golas, C.P.N.P., Nurse Practitioner
Jean Johnston, R.N., Research Nurse Coordinator
Jackie Brady, B.A., Post-baccalaureate Fellow
Aditi Trehan, B.A., M.S., Post-baccalaureate Fellow
Posted: January 6, 2015