Prevalence of Genetic Disorders and GLUT1 Deficiency in a Ketogenic Diet Clinic

Phenotypic and Genotypic Spectrum of Glucose Transporter-1 Deficiency Syndrome

BACKGROUND

Glucose Transporter-1 (GLUT1) Deficiency Syndrome (GLUT1DS) is caused by defective transport of glucose across the blood-brain barrier into brain cells resulting in hypoglycorrhachia due to the heterozygous pathogenic variants in SLC2A1. We report on the phenotypic spectrum of patients with pediatric GLUT1DS as well as their diagnostic methods from a single center in Canada.

METHODS

We reviewed patient charts for clinical features, biochemical and molecular genetic investigations, neuroimaging, treatment modalities, and outcomes of patients with GLUT1DS at our institution.

RESULTS

There were 13 patients. The most common initial symptom was seizures, with the most common seizure type being absence seizures (85%). Seventy-seven percent of the patients had movement disorders, and dystonia and ataxia were the most common movement disorders. Fifty-four percent of the patients did not have a history of developmental delay during their initial presentation, whereas all patients had developmental delay, intellectual disability, or cognitive dysfunction during their follow-up. All patients had a pathogenic or likely pathogenic variant in SLC2A1 and missense variants were the most common variant type.

CONCLUSION

We present 13 patients with GLUT1DS in the pediatric patient population. Atypical clinical features such as hemiplegia and hemiplegic migraine were present in an infant; there was a high prevalence of absence seizures and movement disorders in our patient population. We report an increased number of patients with GLUT1DS since the introduction of next-generation sequencing in the clinical settings. We believe that GLUT1DS should be included in the differential diagnosis of seizures, movement disorders, and hemiplegic migraine.

Epilepsy-Related Voltage-Gated Sodium Channelopathies: A Review

Epilepsy is a disease characterized by abnormal brain activity and a predisposition to generate epileptic seizures, leading to neurobiological, cognitive, psychological, social, and economic impacts for the patient. There are several known causes for epilepsy; one of them is the malfunction of ion channels, resulting from mutations. Voltage-gated sodium channels (NaV) play an essential role in the generation and propagation of action potential, and malfunction caused by mutations can induce irregular neuronal activity. That said, several genetic variations in NaV channels have been described and associated with epilepsy. These mutations can affect channel kinetics, modifying channel activation, inactivation, recovery from inactivation, and/or the current window. Among the NaV subtypes related to epilepsy, NaV1.1 is doubtless the most relevant, with more than 1500 mutations described. Truncation and missense mutations are the most observed alterations. In addition, several studies have already related mutated NaV channels with the electrophysiological functioning of the channel, aiming to correlate with the epilepsy phenotype. The present review provides an overview of studies on epilepsy-associated mutated human NaV1.1, NaV1.2, NaV1.3, NaV1.6, and NaV1.7.

Personalized medicine in genetic epilepsies - possibilities, challenges, and new frontiers

Identifying the optimal treatment based on specific characteristics of each patient is the main promise of precision medicine. In the field of epilepsy, the identification of more than 100 causative genes provides the enticing possibility of treatments targeted to specific disease etiologies. These conditions include classical examples, such as the use of vitamin B6 in antiquitin deficiency or the ketogenic diet in GLUT1 deficiency, where the disease mechanism can be directly addressed by the selection of a specific therapeutic compound. For epilepsies caused by channelopathies there have been advances in understanding how the selection of existing medications can be targeted to the functional consequences of genetic alterations. We discuss the examples of the use of sodium channel blockers such as phenytoin and oxcarbazepine in the sodium channelopathies, quinidine in KCNT1-related epilepsies, and strategies in GRIN-related epilepsies as examples of epilepsy precision medicine. Assessing the clinical response to targeted treatments of these conditions has been complicated by genetic and phenotypic heterogeneity, as well as by various neurological and non-neurological comorbidities. Moving forward, the development of standardized outcome measures will be critical to successful precision medicine trials in complex and heterogeneous disorders like the epilepsies. Finally, we address new frontiers in epilepsy precision medicine, including the need to match the growing volume of genetic data with high-throughput functional assays to assess the functional consequences of genetic variants and the ability to extract clinical data at large scale from electronic medical records and apply quantitative methods based on standardized phenotyping language.