Advances in gene discovery have identified genetic variants in the solute carrier family 6 member 1 (SLC6A1) gene as a monogenic cause of neurodevelopmental disorders, including epilepsy with myoclonic atonic seizures, autism spectrum disorder, and intellectual disability. The SLC6A1 gene encodes for the GABA transporter protein type 1 (GAT1), 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 SLC6A1 variants, the vast majority of which are likely to lead to GAT1 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 analyzed the longitudinal and cell type-specific expression of SLC6A1 in humans and localization of patient and control missense variants in a novel GAT1 protein structure model. In this update, we discuss the progress made in understanding and treating SLC6A1-related disorders thus far, through the concerted efforts of clinicians, scientists, and family support groups.

Neuronal ceroid lipofuscinosis type 7 (CLN7) disease is a lysosomal storage disease caused by mutations in the facilitator superfamily domain containing 8 (MFSD8) gene, which encodes a membrane-bound lysosomal protein MFSD8. To test the effectiveness and safety of adenoassociated viral (AAV) gene therapy, an in vitro study demonstrated that AAV2/MFSD8 dosedependently rescued lysosomal function in fibroblasts from a CLN7 patient. An in vivo efficacy study using intrathecal administration of AAV9/MFSD8 to Mfsd8 -/mice at postnatal day (p)7-10 or p120 with high or low dose led to clear age-and dose-dependent effects. A high dose of AAV9/MFSD8 at p7-10 resulted in widespread MFSD8 mRNA expression, tendency of amelioration of subunit c of mitochondrial ATP synthase accumulation and glial fibrillary acidic protein immunoreactivity, normalization of impaired behaviors, doubled median lifespan, and extended normal body weight gain. In vivo safety studies in rodents concluded that intrathecal administration of AAV9/MFSD8 was safe and well-tolerated. In summary, these results demonstrated that the AAV9/MFSD8 vector is both effective and safe in preclinical models. Investigational New Drug application #19766 to initiate a Phase I intrathecal gene transfer trial for AAV9/MFSD8 was approved by the US FDA and the trial is enrolling CLN7 patients at Children's Health in Dallas, TX in collaboration with UTSW Medical Center (clinicaltrials.gov NCT04737460).

Numerous epidemiologic studies have identified an association between occupational exposures to organophosphorus pesticides (OPs) and asthma or asthmatic symptoms in adults. Emerging epidemiologic data suggest that environmentally relevant levels of OPs may also be linked to respiratory dysfunction in the general population and that in utero and/or early life exposures to environmental OPs may increase risk for childhood asthma. In support of a causal link between OPs and asthma, experimental evidence demonstrates that occupationally and environmentally relevant OP exposures induce bronchospasm and airway hyperreactivity in preclinical models. Mechanistic studies have identified blockade of autoinhibitory M2 muscarinic receptors on parasympathetic nerves that innervate airway smooth muscle as one mechanism by which OPs induce airway hyperreactivity, but significant questions remain regarding the mechanism(s) by which OPs cause neuronal M2 receptor dysfunction and, more generally, how OPs cause persistent asthma, especially after developmental exposures. The goals of this review are to 1) summarize current understanding of OPs in asthma; 2) discuss mechanisms of OP neurotoxicity and immunotoxicity that warrant consideration in the context of OP-induced airway hyperreactivity and asthma, specifically, inflammatory responses, oxidative stress, neural plasticity, and neurogenic inflammation; and 3) identify critical data gaps that need to be addressed in order to better protect adults and children against the harmful respiratory effects of low-level OP exposures.

Dendritic morphology is a critical determinant of neuronal connectivity, and in postganglionic sympathetic neurons, tonic activity correlates directly with the size of the dendritic arbor. Thus, identifying signaling mechanisms that regulate dendritic arborization of sympathetic neurons is important to understanding how functional neural circuitry is established and maintained in the sympathetic nervous system. Bone morphogenetic proteins (BMPs) promote dendritic growth in sympathetic neurons; however, downstream signaling events that link BMP receptor activation to dendritic growth are poorly characterized. We previously reported that BMP7 upregulates p75NTR mRNA in cultured sympathetic neurons. This receptor is implicated in controlling dendritic growth in central neurons but whether p75NTR regulates dendritic growth in peripheral neurons is not known. Here, we demonstrate that BMP7 increases p75NTR protein in cultured sympathetic neurons, and this effect is blocked by pharmacologic inhibition of signaling via BMPR1. BMP7 does not trigger dendritic growth in sympathetic neurons dissociated from superior cervical ganglia (SCG) of p75NTR nullizygous mice, and overexpression of p75NTR in p75NTR−/− neurons is sufficient to cause dendritic growth even in the absence of BMP7. Morphometric analyses of SCG from wildtype versus p75NTR nullizygous mice at 3, 6 and 12–16 weeks of age indicated that genetic deletion of p75NTR does not prevent dendritic growth but does stunt dendritic maturation in sympathetic neurons. These data support the hypotheses that p75NTR is involved in downstream signaling events that mediate BMP7-induced dendritic growth in sympathetic neurons, and suggest that p75NTR signaling positively modulates dendritic complexity in sympathetic neurons in vivo.

Occupational and environmental exposures to organophosphorus pesticides (OPs) are associated with increased incidence of asthma and other pulmonary diseases. Although the canonical mechanism of OP neurotoxicity is inhibition of acetylcholinesterase (AChE), it was previously reported that the OP chlorpyrifos (CPF) causes airway hyperreactivity (AHR) in guinea pigs at levels that do not inhibit lung or brain AChE. The guinea pig is considered to have inherently hyperresponsive airways, thus, cross-species validation is needed to confirm relevance to humans. Additionally, sex differences in asthma incidence have been demonstrated in the human population, but whether OP-induced AHR is sex-dependent has not been systematically studied in a preclinical model. In this study, 8-week old male and female Sprague Dawley rats were administered CPF at doses causing comparable AChE inhibition in whole lung homogenate (30 mg/kg in males, 7 mg/kg in females, sc) prior to assessing pulmonary mechanics in response to electrical stimulation of the vagus nerves at 24 h, 48 h, 72 h, 7 d or 14 d post-exposure in males, and 24 h or 7 d post-exposure in females. CPF significantly potentiated vagally induced airway resistance and tissue elastance at 7 d post-exposure in males, and at 24 h and 7 d post-exposure in females. These effects occurred independent of significant AChE inhibition in cerebellum, blood, trachealis, or isolated airway, suggesting that AChE independent OP-induced airway hyperreactivity is a cross-species phenomenon. These findings have significant implications for assessing the risk posed by CPF, and potentially other OPs, to human health and safety.