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Turning Medical Science into Medical Treatments: The Quest for Translation in Phelan-McDermid Syndrome
by Guest Blogger, Andrew Mitz, Ph.D.
The First International Phelan-McDermid Syndrome Foundation (PMSF) Symposium held earlier this month showed how a small parent-run organization can think and act big! With only 450 registered families worldwide and a mom at the helm, the PMSF put together a first class scientific meeting at the New York Academy of Medicine, by partnering with researchers from the Seaver Autism Center, Mt. Sinai School of Medicine. The goal of the meeting was to chart a course towards medical treatments for this rare, genetic cause of autism. The theme of the meeting was scientific sharing, teamwork, and quality research. Over two days (March 3rd and 4th), the participants heard from families and experts about Phelan-McDermid Syndrome, its history, its connection to autism spectrum disorders, and the very latest in scientific approaches. They also learned how people studying other disorders have found fast paths to drug development.
The early presentation by Dr. Catalina Betancur (INSERM, France) provided two key foundational scientific links to help open the meeting. First, she showed that Phelan-McDermid Syndrome, also called 22q13 Deletion Syndrome, is one of many known genetic causes or risk factors of autism spectrum disorders. Second, virtually all cases of chromosome 22 abnormalities that cause Phelan-McDermid Syndrome share damage to or loss of the SHANK3 gene as a common feature. SHANK3 gene mutations are also found in about 1% of the general autism population. That is why understanding the biology of SHANK3, and how to treat the loss of SHANK3 in Phelan-McDermid Syndrome patients, resonated through every talk of the meeting.
The SHANK3 gene encodes a protein called Shank3 that is critical for proper synapse function. Synapses are the junctions or contact points between neurons of the brain, where information is exchanged. Thanks to the elegant and detailed descriptions provided by Dr. Tobias Boeckers (Ulm University, Germany), participants learned how Shank3 proteins stick to each other. The proteins form an interlocking network that acts as a backbone for the synapse both mechanically and chemically. For this reason, Shank3 (also known as ProSAP2) is called a scaffolding protein. Dr. Boeckers showed how the loss of Shank3 in Phelan-McDermid Syndrome makes the entire synaptic junction unstable. Shank3 is one of the first proteins required for synapse formation, which is constantly taking place in the brain. Dr. Carlo Sala (University of Milan, Italy), another pioneer in SHANK3 research, explained that proper synapse formation and stability are essential processes for learning and memory.
In a particularly memorable session on the first day, Dr. Boeckers and other investigators including Dr. Joseph Buxbaum (Mount Sinai School of Medicine), Dr. Craig Powell (University of Texas), and Dr. Yong-Hui Jiang (Duke University) shared details about their respective efforts to develop a Phelan-McDermid Syndrome mouse model with a mutated or deleted SHANK3 gene. The open and frank exchange resulted in a greater appreciation among the participants of the methodological challenges they share, and underscored how unfettered sharing of information can accelerate scientific progress as it helps reduce duplication and facilitates exploration of a greater range of possible solutions. The families with Phelan-McDermid Syndrome looked on in great appreciation as the scientists ventured outside their normal comfort zone to openly share “intimate” (unpublished) details of their research.
Dr. Ricardo Dolmetsch (Stanford University) described his cutting-edge work on induced pluripotent stem cells (iPS cells). He takes tiny skin samples from patients and, using a special protein cocktail, ”reprograms” them. The painstaking process takes many months to first produce stem cells, and then neurons. Amazingly, Dr. Dolmetsch showed that these neurons behave much like the neurons studied in animal models, which validates both his work and the animal models. With his iPS-generated neurons in hand, Dr. Dolmetsch plans to test compounds to see which ones are most effective in reversing the deficits seen in these cells.
Dr. Sala studies animal neurons using another experimental approach called “knockdown”. He simulates what happens in Phelan-McDermid Syndrome patients missing one of their SHANK3 genes by interfering with the production of Shank3 protein. When Shank3 is knocked down, Dr. Sala noticed a reduction in a receptor called mGluR5. This receptor is normally active during communication between neurons. mGluR5 mobilizes other signaling molecules, gene expression and production of other synaptic proteins. Dr. Sala showed that it is possible to partially restore much of these functions by applying a drug that stimulates the remaining mGluR5 receptors and activates related molecular pathways. This work is vital for identifying potential biological targets for drug development.
In the quest for a quick and efficient path to new therapeutics, Dr.Ozlem Bozdagi Gunal (Mount Sinai School of Medicine) presented exciting new results. Using “knockout” mice missing one SHANK3 gene, she looked to see what known drugs could correct at least some of the synaptic defects. She showed that the structural defects in the synapse lead to failures in the way it functions, especially during learning. The research team identified a drug that allows a particular well-studied form of synaptic strengthening, called long term potentiation, to proceed normally in spite of deficits in Shank3.
