SLC13A5 Clinical Overview
Dr. Porter discussed the common symptoms of SLC13A5 Deficiency in children, including seizures in the first days of life, a distinct movement disorder, speech difficulties, and tooth abnormalities. There is no or minimal brain structural problem in the brain MRI. This disease does not appear to be a progressive, degenerative condition. The EEG background can be normal. Seizure burden varies widely in both type and frequency. The children are very sociable. Epilepsy is one small component of the disorder. Movement and motor control as well as cognitive delays are prominent.
SLC13A5 Research Overview
Dr. Bainbridge discussed what we have learnt from the research done since the identification of children with SLC13A5 mutations. SLC13A5 Deficiency is autosomal recessive with most of the mutations resulting in loss of citrate transport function. There are about 25 different disease-causing mutations known in the 70 children identified world-wide. However, many effected children seem to be unreported or undiagnosed. Dr. Bainbridge stressed on the fact that SLC13A5 not only transports citrate but also other metabolites like succinate and malate and we need to study all the functions of the transporter. Also, citrate is involved in many cellular functions like energy metabolism, ion chelation, fatty acid synthesis and regulation of protein expression, which needs to be understood in context with the symptoms exhibited by children with SLC13A5 Deficiency to find a cure.
Tooth abnormalities in SLC13A5 Deficiency
One of the hallmark symptoms of SLC13A5 Deficiency is abnormal tooth enamel. Abnormalities in the formation of enamel are a common symptom ofKohlschütter-Tönz Syndrome, which is caused by mutations in either the ROGD1 gene or the SLC13A5 gene. Patients with SLC13A5 mutations appear to have an enamel abnormality called Hypoplastic Amelogenesis Imperfecta. On the other hand, patients with ROGD1 mutations appear to have Hypocalcified Amelogenesis Imperfecta. Citrate is an important component in tooth development and is also a chelator for calcium, which is a mineral component of the structure of a tooth.
What can Human SLC13A5 mutations in Drosophila tell us about the SLC13A5 syndrome?
Dr. Helfand and his team has created humanized flies which have either normal human SLC13A5 gene or mutated (G219R or L429P mutation) human SLC13A5 gene. The normal humanized flies were healthy while the mutant humanized flies were lethal. Dr Helfand suspects that the mutant human SLC13A5 gene might have a toxic gain of function. Dr Helfand’s team is working on finding out if mutations in any other gene in these flies can suppress the toxicity caused in the G219R humanized flies. They also want to test whether reducing the expression of human mutant slc13a5 gene (through RNAi) could rescue lethality in flies.
Humanized SLC13A5 mouse to understand the role of the citrate transporter in humans
Dr. Ganapathy explained that there are functional differences between the fly, mouse and human SLC13A5 transporter. This citrate transporter has different substrate affinity as well as mechanism of citrate transport across different species. He further discussed the subtle neurological phenotype that his team observed in SLC13A5 knock-out (KO) mice where the KO mice exhibit lesser behavioral, mobility and cognitive abilities than the normal mice. The KO mice were more susceptible to intense seizures under the influence of a seizure-inducing compound called Pilocarpine. His team has created a humanized SLC13A5 mice where they exchanged the mice SLC13A5 with the human SLC13A5 and found that mice with human SLC13A5 is more prone to weight gain on high fat diet compared to normal or SLC13A5 KO mice. The major conclusion of his talk was that, as the mouse SLC13A5 shows marked differences in citrate transport function compared to human SLC13A5, the humanized SLC13A5 is likely to be useful as a more appropriate animal model to investigate the biological role of the citrate transporter in humans.
Untargeted Metabolomic Profiling in SLC13A5 Deficiency
Dr. Elsea studies various metabolic disorders. She discussed the importance of studying the metabolome (levels of different metabolites in patient samples) of patients or disease models in understanding the disease mechanism and finding biomarkers for the disease. She presented her study on the metabolomic analysis of Slc13a5 KO mice and compared it with the metabolomic analysis of the SLC13A5 deficiency patients published recently (https://www.mgmjournal.com/article/S1096-7192(17)30289-5/abstract). Citrate levels were found elevated in the CSF of both the Slc13a5 KO mice and the SLC13A5 deficiency patients.
The metabolic function of NaCT in neurons
A team of Dr Ana Pajor, Dr Anne Murphy, Dr Christian Metallo and Dr Thekla Cordes at UC San Diego is working on finding the role of the SLC13A5 citrate transporter in rat neurons and human cell metabolism. They studied the respiration and energy consumption in the rat neurons in the presence of citrate and found that citrate influences these processes if the cells are treated for longer periods with citrate. They also traced the citrate in rat neurons and human liver cells and found that it is utilized in making fatty acids in these cells. The team also discussed that they have successfully created SLC13A5 KO human liver cells using CRISPR technology. These cells can be used in studying the disease mechanism as well as drug screening. They discussed their plans to continue these studies in patient-derived iPSCs.
3D cortical spheroids as disease model for SLC13A5 Deficiency
Dr. Ezashi discussed his work on stem cells using the early onset Preeclampsia which is a pregnancy disorder. He discussed the importance of the patient derived iPSCs in studying various diseases and explained how they can be beneficial in studying the SLC13A5 Deficiency. His team has created iPSCs for two SLC13A5 Deficiency patients and proposed to create more for studying the mechanism and discover biomarkers for the disease.
AAV Gene Therapy for SLC13A5 Deficiency
Dr. Bailey discussed her pioneering work in using AAV9 vector for gene therapy in neuronal diseases especially in the GAN (Giant Axonal Neuropathy) gene therapy preclinical studies, which successfully led to GAN clinical trials. She discussed the experiments that are necessary to show the safety and efficacy of the gene therapy in animal or cell models of a disease before introducing it to the patients. She also shared her preliminary studies on the AAV9 vector designed for SLC13A5 Deficiency gene therapy and the toxicity experiments done in mice. She presented her proposal to continue the toxicity and efficacy studies for SLC13A5 gene therapy in mice.
Rare Disease Drug Development
In her talk, Ms. Blessing shared her industry experience on drug development for rare diseases. She discussed the efforts of Congress and FDA to enable the biopharmaceutical industry to develop drugs for rare disorders by introducing new pathways to expedite the regulatory process for rare disease. She also discussed the value and the importance in coordination between patient centered disease foundations, like TESS Research Foundation, scientists & clinicians, and industry. She stressed the value in disease models, biomarkers, and patient registries in facilitating efficient development of therapeutics for rare diseases.
Initiatives at TESS Research Foundation
Dr Dubey discussed the new initiatives at TESS Research Foundation including Creation of the patient registry (database) using RedCap, creation of a bio-bank of the patient/ family blood and tissue samples at Coriell Institute for Medical Research, NJ and creation of patient-derived IPSCs. All the three projects are initiated to facilitate the centralized collection of the patient information to be distributed to interested researchers in an efficient and cost effective manner. These projects will save time and money and ensure availability of sufficient patient information and samples for various research and clinical studies. They will also save the time and effort that patients and their families have to put in giving the same information or samples multiple times. TESS Research Foundation frequently updates the website to keep the entire SLC13A5 community informed about latest research, progress made and new opportunities.
Our first two Research Roundtables in 2015 and 2017 included TESS Grantees sharing research updates for both families and professionals. We have expanded and grown to include a broader community. We look forward to seeing you at our next event!