Ketogenic diet. The ketogenic diet (KD) has been formally used to treat epilepsy for the past 100 years. Its history of use dates to Hippocrates who realized that while people with epilepsy fasted their seizures improved. The ketogenic diet mimics a long-term fasting state by having the body enter ketosis with a high fat low carbohydrate + protein diet.
Precision therapeutics. Ongoing research in precision therapies in neurological disorders, including 15q-related disorders, is occurring in three spaces: 1) gene therapy, 2) anti-sense oligonucleotides (ASOs), and 3) small molecules (repurposing existing drugs or generating new drugs), where the latter is primarily focused on addressing the symptoms of genetic disorders (i.e. seizures) rather than the cause (i.e gene dysfunction). Each of these forms of therapy has particular challenges, including, critically, the delivery method. The blood-brain barrier (doing its job well) restricts the access of large or hydrophilic medications to the central nervous system (CNS), therefore scientists building these drugs must not only consider efficacy and safety of the drug itself, but also efficacy and safety of the delivery method to the CNS. Below we explore ASOs and gene therapies and their application in 15q-related disorders in more depth. We will not discuss small molecule therapies here as the topic is too broad in scope for the purposes of this post, and we would like to focus primarily on genetically-based therapies.
NDD. Family-based (trio) exome sequencing has become the standardized method for identifying genetic etiologies that cause neurodevelopmental disorders. De novo variants have been responsible for the majority of pathogenic genetic findings, although the landscape of genetic disorders overall is highly heterogeneous. In a recently published study, the authors assessed variant classification to identify new molecular diagnoses and factors influencing the likelihood of receiving a diagnosis. The study reported a diagnostic yield of over 41%, highlighting 60 new genes associated with developmental disorders. The authors also emphasized the importance of structured and detailed phenotypic information for improving variant interpretation. This blog post provides a brief review of their publication in the context of improving diagnostic yield using a phenotypically driven approach in rare diseases.
One region, three disorders. The following blogpost serves as a partner to this week’s earlier post on the genomic idiosyncrasies of the 15q11-13 region. We hope that the discussion of the clinical aspects of disorders rooted in this region will further illustrate the vast complexity of the genome. Below we describe the three clinical syndromes associated with this region.
Cytogenetics. 15q11-13 can be an intimidating region, even for many seasoned genetics professionals. Several factors contribute to this, including a complex genomic architecture, genomic imprinting, an acrocentric chromosome, and several genes critical to neurological function. For today’s blog post, we’ll try to unravel some of its complexity to make interpretation of copy number variants (CNVs) in this area clearer.
ATP1A2. We have previously written about ATP1A3, one of the neuronal ATPases, which, together with ATP1A2, actively works to maintain the electrochemical gradient across cell membranes. In our previous post, we likened ATP1A3 to Sisyphus, who was punished by the gods to spend eternity exerting his strength to push a boulder up a hill, only for the boulder to roll back down, over and over again. Similarly, the ATPases utilize energy (ATP) to transport Na+ out of the cell and K+ into the cell, even while other voltage-gated channels effortlessly open to allow Na+ and K+ to move in the opposite direction, forcing the boulder back down the hill. However, from another perspective we can see that far from being Sisyphus, the ATPases are the noblest of facilitators, proudly maintaining the membrane electrochemical gradient in order to enable all other cell processes to function. If you will allow me further anthropomorphization of submicroscopic proteins – far from being inconsiderate to the task of the ATPases, our voltage-gated Na+, K+, and Ca++ channels are reliant on these stoic transporters to get their jobs done. It is because of the electrochemical gradient that cells are able to propagate action potentials down an axon, signal axon terminals to release neurotransmitters, and continue to send electrochemical signals on to subsequent cells. Both ATP1A2 and ATP1A3 code for subunits of the Na+-K+ ATPase, where ATP1A2 codes for the α2 subunit and ATP1A3 for the α3 subunit. Both ATP1A3 and ATP1A2 are expressed in neurons during embryonal brain development, and while ATP1A3 remains neuronal postnatally, ATP1A2 is relegated to the glial cells postnatally and into adulthood. In addition to their role in active ion transport, Na+-K+ ATPases are thought to play a part in regulating signaling pathways and gene transcription. Given its localization to astrocytes, which act as a so-called “glutamate sink” to prevent glutamate excitotoxicity within the synapse, ATP1A2 is thought to be critical for the process of glutamate clearance and prevention of excitotoxicity (Du et al 2020).
Nurse practitioners. Last month was nurses’ month – yes that’s correct, we have been upgraded from the previous nurses’ week. As the month comes to an end, I would like to briefly reflect on the role of the nurse practitioner (NP) in the epilepsy field.
GRIA genes. This is the first time we are describing GRIA genes on this blog. GRIA genes, which include GRIA1, GRIA2, GRIA3, and GRIA4, encode the AMPA receptor, one of the two key channels in the process of glutamate neurotransmission. While GRIN genes, which encode the NMDA receptor, have been characterized much more extensively in the literature, GRIAs remain relatively under-characterized, even though their protein products are involved in a similar molecular process in the post-synapse in modulating excitatory synaptic transmission. Here, we provide a brief overview of the genetic and phenotypic range of GRIA-related disorders.