Current knowledge of SLC6A1-related neurodevelopmental disorders.

Advances in gene discovery have identified genetic variants in the solute carrier family 6 member 1 gene as a monogenic cause of neurodevelopmental disorders, including epilepsy with myoclonic atonic seizures, autism spectrum disorder and intellectual disability. The solute carrier family 6 member 1 gene encodes for the GABA transporter protein type 1, which is responsible for the reuptake of the neurotransmitter GABA, the primary inhibitory neurotransmitter in the central nervous system, from the extracellular space. GABAergic inhibition is essential to counterbalance neuronal excitation, and when significantly disrupted, it negatively impacts brain development leading to developmental differences and seizures. Aggregation of patient variants and observed clinical manifestations expand understanding of the genotypic and phenotypic spectrum of this disorder. Here, we assess genetic and phenotypic features in 116 individuals with solute carrier family 6 member 1 variants, the vast majority of which are likely to lead to GABA transporter protein type 1 loss-of-function. The knowledge acquired will guide therapeutic decisions and the development of targeted therapies that selectively enhance transporter function and may improve symptoms. We analysed the longitudinal and cell type-specific expression of solute carrier family 6 member 1 in humans and localization of patient and control missense variants in a novel GABA transporter protein type 1 protein structure model. In this update, we discuss the progress made in understanding and treating solute carrier family 6 member 1-related disorders thus far, through the concerted efforts of clinicians, scientists and family support groups.

Increased expression of L-amino acid transporters in balloon cells of tuberous sclerosis.

OBJECTS: Tuberous sclerosis complex (TSC) is a dysgenetic syndrome involved in multiple organs, and the pathognomonic cortical tuber act as an epileptic substrate. The amino acid transport system L (LAT) is a major nutrient transport system, and LAT1 is highly expressed in malignant tumors to support tumor cell growth. To study the life-long epilepsy from the cortical tuber, the expression of LAT1 in balloon cells and dysplastic neurons of the cortical tuber is investigated. MATERIALS AND METHODS: LAT1 expression was investigated by LAT1 mRNA using reverse transcription-polymerase chain reaction and immunohistochemical staining with anti-human LAT1 antibody in nine patients with TSC and three control brains. CONCLUSION: LAT1 mRNA was detectable only in fresh-frozen tissues of TSC, and it was upregulated in the cortical tuber lesion. While the LAT1 immunopositivity of control brains was limited in the capillary endothelial cells in the gray matter, increased LAT1 immunopositivity was noted in balloon cells of the cortical tubers in addition to the capillary endothelial cells as shown in control brains. Linear and strong immunopositivity along the cell membrane and cytoplasm of the balloon cells, and weakly granular immunopositivity in their cytoplasm were noted. Increased expression of LAT1 in the balloon cells is important for the active transport of large neutral amino acids into the balloon cells, and that the biologic process may play an important role in the active protein synthesis with metabolic maintenance of balloon cells in cortical tubers of patients with TSC.

Glutaric aciduria type 1 in Korea: report of two novel mutations.

Glutaric aciduria type I (GA I) is an autosomal recessive disorder caused by a deficiency of glutaryl-CoA dehydrogenase. Although over 400 patients confirmed as GA I have been reported, reports from the Asian population had contributed to the minor proportion. We recently diagnosed two cases of GA I confirmed with mutational analysis. Here, we present their rather atypical clinical presentations with genetic characteristics for the first time in Korea. Profound developmental delay from birth, association of hearing loss, and neurological improvement after surgical intervention, were considered to be different clinical features from most reported cases. One patient was a compound heterozygote for p.Ser139Leu and p.Asp220Tyr, and the other for p.Ser139Leu and Glu160X. The mutations of the two alleles (p.Asp220Tyr and p.Glu160X) were novel and reports of p.Ser139Leu were rare both in Western and other Asian populations. These might suggest different genetic spectrum of Korean GA I patients.