GLUT1 Deficiency Research Articles

Long-Term Effects of a Classic Ketogenic Diet on Ghrelin and Leptin Concentration: A 12-Month Prospective Study in a Cohort of Italian Children and Adults with GLUT1-Deficiency Syndrome and Drug Resistant Epilepsy.

The classical ketogenic diet (cKD) is an isocaloric, high fat, very low-carbohydrate diet that induces ketosis, strongly influencing leptin and ghrelin regulation. However, not enough is known about the impact of a long-term cKD. This study evaluated the effects of a 12-month cKD on ghrelin and leptin concentrations in children, adolescents and adults affected by the GLUT1-Deficiency Syndrome or drug resistant epilepsy (DRE). We also investigated the relationship between the nutritional status, body composition and ghrelin and leptin variations. We carried out a longitudinal study on 30 patients: Twenty-five children and adolescents (15 females, 8 ± 4 years), and five adults (two females, 34 ± 16 years). After 12-monoths cKD, there were no significant changes in ghrelin and leptin, or in the nutritional status, body fat, glucose and lipid profiles. However, a slight height z-score reduction (from −0.603 ± 1.178 to −0.953 ± 1.354, p ≤ 0.001) and a drop in fasting insulin occurred. We found no correlations between ghrelin changes and nutritional status and body composition, whereas leptin changes correlated positively with variations in the weight z-score and body fat (ρ = 0.4534, p = 0.0341; ρ = 0.5901, p = 0.0135; respectively). These results suggest that a long-term cKD does not change ghrelin and leptin concentrations independently of age and neurological condition.

Quality of Life in Chronic Ketogenic Diet Treatment: The GLUT1DS Population Perspective.

Background: Glucose transporter type 1 deficiency syndrome (GLUT1DS) is a rare, genetically determined neurological disorder, for which Ketogenic Diet (KD) represents the gold standard life-long treatment. The aim of this study is to investigate health related quality of life in a well characterized cohort of patients affected by GLUT1DS treated with KD, evaluating factors that can influence patients’ and parents’ quality of life perception. Methods: This is a double center exploratory research study. A postal survey with auto-administrable questionnaires was conducted among 17 subjects (aged 3–22 years) with diagnosis of GLUT1DS, receiving a stable KD treatment for more than 1 year. The Pediatric Quality of Life Inventory (PedsQL) 4.0 Generic Core Scales was adopted. Clinical variables analyzed in relation to quality of life were frequency of epileptic seizures and movement disorder since KD introduction, presence of intellectual disability (ID), and KD ratio. Results: Quality of life global scores were impaired both in parents’ and children’s perspectives, with a significant concordance. Taking into consideration subscales, the average was 64.17 (range 10–100) for physical functioning, 74.23 (range 30–100) for emotional functioning, 62.64 (range 10–100) for social functioning, and 56 (range 15–92) for school functioning. Conclusions: In patients with GLUT1DS the quality of life perception is comparable to that of other patients with chronic disease. In our sample, the presence of movement disorder seems to be a crucial element in quality of life perception.

Impact of the ketogenic diet on human gut

Background: The classic ketogenic diet (KD) is an normocaloric dietary protocol with a high intake of fats (85–90% of energy), which is used as a therapy for drug-resistant epilepsies and type 1 glucose transporter deficiency syndromes (GLUT1-DS). It is known that specific dietetic patterns can influence the composition of the intestinal microbiota; in particular, it was shown that KD is associated with various pro-inflammatory changes in the microbiota. Aim of the study is to verify the impact of KD on the intestinal microbiota, through the evaluation of: intestinal bacterial composition, markers of bacterial metabolism (short chain fatty acids, SCFA), toxicity of faecal water.

Developmental outcomes and prevalence of SLC2A1 variants in young infants with hypoglycorrhachia

IntroductionThe neurodevelopmental outcomes of young infants with hypoglycorrhachia that is comparable to glucose transporter 1 deficiency syndrome (GLUT1DS), i.e. cerebrospinal fluid (CSF) glucose ≤40 mg/dL and CSF lactate <2.2 mM without causes of secondary hypoglycorrhachia are unknown. This study investigated the developmental outcomes and possibility of GLUT1DS in infants with hypoglycorrhachia, or low CSF glucose concentration. Material and methods1655 neurologically asymptomatic infants aged <4 months had CSF examinations for fever workup from 2006 to 2016. Among the infants with normal CSF cell counts and without isolated pathogens, there were hypoglycorrhachia group who had CSF glucose levels that were comparable to GLUT1DS, and age- and gender-matched non-hypoglycorrhachia group. Both groups were at a mean age of 5.9 ± 2.4 years (ranged 1–10 years) at neurodevelopmental evaluation in 2017. Mutational analysis of solute-carrier-family 2, which facilitated the glucose transporter member 1 (SLC2A1) gene was performed. ResultsAmong the 722 infants with normal CSF cell counts and without isolated pathogens, 30 (4.2%) had hypoglycorrhachia that was comparable to GLUT1DS. In the 25 infants with hypoglycorrhachia available for follow-up, 4 (16%) had abnormal outcomes, of which 3 (12%) had the history of mixed-type developmental delay before age 6 and 1 (4%) had type 1 diabetes mellitus. In the non-hypoglycorrhachia control group (n = 50), 2 patients (4%) showed abnormal outcomes, both with the history of pure speech delay. The hypoglycorrhachia group had a higher rate of the history of mixed-type of developmental delay than the control group (12% vs. 0%, P = 0.034). No SLC2A1 pathogenic variants were observed in the hypoglycorrhachia group. ConclusionHypoglycorrhachia may be a potential biomarker for neurodevelopmental delay instead of for GLUT1DS in neurologically asymptomatic young infants.

Jeavons syndrome in a family with GLUT1-deficiency syndrome

Jeavons syndrome in a family with GLUT1-deficiency syndrome

053 GLUT-1 deficiency presenting as dopa-responsive dystonia: an atypical phenotype of a rare disease

IntroductionThe SLC2A1 gene encodes the glucose transporter GLUT1, responsible for normal glucose transport across the blood-brain barrier. Mutations in this gene have classically been associated with an epileptic encephalopathy referred to as GLUT-1 Deficiency Syndrome, which typically presents with early-onset refractory epilepsy, developmental delay and complex movement disorders.1 2 More recently, SLC2A1 variants have been identified in patients with paroxysmal exercise-induced dyskinesia (PED), with or without a history of epilepsy.3 4 Response to medication is typically poor; however, both seizures and dyskinesia may improve following implementation of a ketogenic diet.5 A single case of levodopa responsiveness has previously been described in a subject with SLC2A1 mutation and PED.5Methods and resultsWe describe a 47-year-old female with mild intellectual disability since childhood but no history of epilepsy, who developed episodic dystonia affecting the lower limbs in her early 20’s. A clinical diagnosis of dopa-responsive dystonia was made following a marked, sustained response to levodopa. There was no significant family history. In her 40’s she developed breakthrough dystonia with exertion and choreiform movements affecting the fingers and face. A subsequent dystonia panel identified a heterozygous variant c.[1199G&gt;T];[=] (p.Arg400Leu) in the SLC2A1 gene. Cerebrospinal fluid glucose concentration was low (2.0 mmol/L). She declined a trial of a ketogenic diet.SLC2A1 variants are associated with PED; however, response to levodopa has not been widely reported.ConclusionIt is becoming increasingly evident that the phenotypic presentations of GLUT1 deficiency are diverse, and SLC2A1 testing should be considered in a broader range of patients.ReferencesWang, D, Kranz-Eble P, De Vivo DK. Mutational analysis of GLUT1 (SLC2A1) in Glut-1 Deficiency Syndrome. Human Mutation 2001;16:224–231.Klepper J, Leiendecker B. GLUT1 deficiency syndrome – 2007 update. Developmental Medicine &amp; Child Neurology 2007;49:707–716.Schneider SA, Paisan-Ruiz C, Garcia-Gorostiaga I, Quinn NP, Weber YG, et al. GLUT1 gene mutations cause sporadic paroxysmal exercise-induced dyskinesias. Mov Disord 2009;24(11):1684–1696.Suls A, Dedeken P, Goffin K, Van Esch H, Dupont P. Paroxysmal exercise-induced dyskinesia and epilepsy is due to mutations in SLC2A1, endoding the glucose transporter GLUT1. Brain 2008;131:1831–1844.Baschieri F, Batla A, Erro R, Ganos C, Cordivari C, Bhatia KP. Paroxysmal exercise-induced dystonia due to GLUT-1 mutation can be responsive to levodopa: a case report. J Neurol 2014;261:615–616.

Ketogenic Diet in Patients with GLUT1 Deficiency Syndrome.

Background:The ketogenic diet (KD) is a high fat, low carbohydrate diet considered to be the treatment of choice for GLUT1deficiency syndrome, a metabolic disorder affecting the nervous system. Aim:To present our experience in four patients with GLUT1 deficiency syndrome who were treated with KD. Methods:Retrospective data from case series. Phenotypical features, mainly movement disorder and seizures, are being described for each patient. All four cases are currently following the Modified Atkins Diet. Results:The response to ketogenic diet in our four patients was significant with improvement of movement disorder or seizures control. Conclusion:The ketogenic diet is the treatment of choice for GLUT1deficiency syndrome. Recognition of the disorder is the key for appropriate management among clinicians. Diet compliance is an important issue in school age children.

Estudio de pacientes pediátricos con fenotipo clínico y bioquímico de síndrome de déficit de transportador de glucosa cerebral (GLUT-1)

IntroductionGlucose transporter type 1 (GLUT1) deficiency syndrome may present a range of phenotypes, including epilepsy, intellectual disability, and movement disorders. The majority of patients present low CSF glucose levels and/or defects in the SLC2A1 gene; however, some patients do not present low CSF glucose or SLC2A1 mutations, and may have other mutations in other genes with compatible phenotypes. AimsWe describe the clinical, biochemical, and genetic characteristics of the disease and perform a univariate analysis of a group of patients with clinical and biochemical phenotype of GLUT1 deficiency syndrome, with or without SLC2A1 mutations. Material and methodsThe study included 13 patients meeting clinical and biochemical criteria for GLUT1 deficiency syndrome. SLC2A1 sequencing and multiplex ligation-dependent probe amplification were performed; exome sequencing was performed for patients with negative results. ResultsSix patients presented the classic phenotype; 2 paroxysmal dyskinesia, 2 complex movement disorders, 2 early-onset absence seizures, and one presented drug-resistant childhood absence epilepsy. Six patients were positive for SLC2A1 mutations; in the other 5, another genetic defect was identified. No significant differences were observed between the 2 groups for age of onset, clinical presentation, microcephaly, intellectual disability, or response to ketogenic diet. Patients with SLC2A1 mutations presented more clinical changes in relation to diet (66.7% vs. 28.6% in the SLC2A1-negative group) and greater persistence of motor symptoms (66% vs. 28.6%); these differences were not statistically significant. Significant differences were observed for CSF glucose level (34.5 vs. 46mg/dL, P=.04) and CSF/serum glucose ratio (0.4 vs. 0.48, P<.05). ConclusionsGLUT1 deficiency syndrome may be caused by mutations to genes other than SLC2A1 in patients with compatible phenotype, low CSF glucose level, and good response to the ketogenic diet.

Glut1 deficiency is a rare but treatable cause of childhood absence epilepsy with atypical features

Glucose transporter type 1 deficiency syndrome (GLUT1-DS) is a rare genetic disorder caused by pathogenic variants in SLC2A1, resulting in impaired glucose uptake through the blood-brain barrier. Our objective is to analyze the frequency of GLUT1-DS in patients with absences with atypical features. Sequencing analysis and detection of copy number variation of the SLC2A1 gene was carried out in patients with atypical absences including: early-onset absence, intellectual disability, additional seizure types, refractory epilepsy, associated movement disorders, as well as those who have first-degree relatives with absence epilepsy or atypical EEG ictal discharges. Of the 43 patients analyzed, pathogenic variations were found in 2 (4.6%). Six atypical characteristics were found in these 2 patients. The greater the number of atypical characteristics presenting in patients with absence seizures, the more likely they have a SLC2A1 mutation. Although GLUT1-DS is an infrequent cause of absence epilepsy, recognizing this disorder is important, since initiation of a ketogenic diet can reduce the frequency of seizures, the severity of the movement disorder, and also improve the quality of life of the patients and their families.

Impact of pathogenic mutations of the GLUT1 glucose transporter on channel dynamics using ConsDYN enhanced sampling

Background: The solute carrier (SLC) family of membrane proteins is a large class of transporters for many small molecules that are vital for the cell. Several pathogenic mutations are reported in the glucose transporter subfamily SLC2, causing Glut1-deficiency syndrome (GLUT1DS1, GLUT1DS2), epilepsy (EIG2) and cryohydrocytosis with neurological defects (Dystonia-9). Understanding the link between these mutations and transporter dynamics is crucial to elucidate their role in the dysfunction of the underlying transport mechanism. Methods: Predictions from SIFT and PolyPhen provided an impression of the impact upon mutation in the highly conserved RXGRR motifs, but no clear differentiation could be made by these methods between pathogenic and non-pathogenic mutations. Therefore, to identify the molecular effects on the transporter function, insight from molecular dynamic simulations is required. We studied a variety of pathogenic and non-pathogenic mutations, using a newly developed coarse-grained simulation approach ‘ConsDYN’, which allows the sampling of both inward-open and outward-occluded states. To guarantee the sampling of large conformational changes, we only include conserved restraints of the elastic network introduced upon coarse-graining, which showed similar reference distances between the two conformational states (≤1 Å difference). Results: We capture the ‘conserved dynamics’ between both states using ConsDYN. Simultaneously, it allowed us to considerably lower the computational costs of our study. This approach is sufficiently sensitive to capture the effect of different mutations, and our results clearly indicate that the pathogenic mutation in GLUT1, G91D, situated at the highly conserved RXGRR motif between helices 2 and 3, has a strong impact on channel function, as it blocks the protein from sampling both conformational states. Conclusions: Using our approach, we can explain the pathogenicity of the mutation G91D when we observe the configurations of the transmembrane helices, suggesting that their relative position is crucial for the correct functioning of the GLUT1 protein.

Screening of SLC2A1 in a large cohort of patients suspected for Glut1 deficiency syndrome: identification of novel variants and associated phenotypes.

Glucose transporter type 1 deficiency syndrome (Glut1 DS) is a rare neurological disorder caused by impaired glucose delivery to the brain. The clinical spectrum of Glut1 DS mainly includes epilepsy, paroxysmal dyskinesia (PD), developmental delay and microcephaly. Glut1 DS diagnosis is based on the identification of hypoglycorrhachia and pathogenic mutations of the SLC2A1 gene. Here, we report the molecular screening of SLC2A1 in 354 patients clinically suspected for Glut1 DS. From this cohort, we selected 245 patients for whom comprehensive clinical and laboratory data were available. Among them, we identified 19 patients carrying nucleotide variants of pathological significance, 5 of which were novel. The symptoms of onset, which varied from neonatal to adult age, included epilepsy, PD or non-epileptic paroxysmal manifestations. The comparison of the clinical features between the 19 SLC2A1 mutated and the 226 non-mutated patients revealed that the onset of epilepsy within the first year of life (when associated with developmental delay or other neurological manifestations), the association of epilepsy with PD and acquired microcephaly are more common in mutated subjects. Taken together, these data confirm the variability of expression of the phenotypes associated with mutation of SLC2A1 and provide useful clinical tools for the early identification of subjects highly suspected for the disease.

How often is antiseizure drug-free ketogenic diet therapy achieved?

The ketogenic diet (KD) is often started not only for seizure reduction but also to potentially wean antiseizure drugs (ASDs) in children with epilepsy. Although there have been several publications regarding ASD reduction on the KD, it is unknown how often complete medication withdrawal occurs. We reviewed the charts of all children started on the KD at Johns Hopkins Hospital and Johns Hopkins All Children's Hospital from 1/11 to 4/18. Children were defined as achieving drug-free diet (DFD) status if they started the KD on at least 1 ASD and achieved a period of time where they were on the KD alone. Over the time period, 232 children were evaluated; DFD status occurred in 43 (18.5%), of which 32 (13.8% of the full cohort) remained off ASDs for the remainder of their KD treatment course. Eleven children restarted ASD after a mean of 7 months. Children achieving DFD therapy were more likely to be younger, have fewer ASDs at KD onset, have Glut1 deficiency or epilepsy with myoclonic–atonic seizures, but were less likely to have Lennox–Gastaut syndrome or a gastrostomy tube.

Failure of ketogenic diet therapy in GLUT1 deficiency syndrome.

Epilepsy in GLUT1 deficiency syndrome is generally drug-resistant; ketogenic diet (KD) therapy is the mainstay of therapy, as production of ketones provides the brain with an alternative energy source, bypassing the defect in GLUT1. Failure of KD therapy and risk factors for failure have been sparsely published. We performed a retrospective study of GLUT1DS patients with refractory epilepsy failing on KD therapy, to identify their clinical characteristics. Failure of the ketogenic diet was due to KD inefficacy (poor effect despite adequate ketosis), as well as intolerance and an inability to attain ketosis. Our cohort of seven patients in whom KD therapy failed stood out for their advanced age at seizure onset, i.e. almost 4 years vs 8 months in large series, female sex, as well as their advanced age at diagnosis and initiation of KD therapy. EEG recordings during KD therapy can aid in the assessment of effectiveness of the KD therapy. GLUT1DS is generally described as a treatable disorder and existing case series do not provide details of treatment failure. In select patients with GLUT1DS, KD therapy fails, rendering GLUT1DS an essentially untreatable disorder. Failure of the ketogenic diet was due to KD inefficacy (poor effect despite adequate ketosis), as well as intolerance and an inability to attain ketosis. Failure to reduce seizure frequency with deterioration of the EEG findings should lead to consideration of cessation of KD therapy.

New insights into GluT1 mechanics during glucose transfer

Glucose plays a crucial role in the mammalian cell metabolism. In the erythrocytes and endothelial cells of the blood-brain barrier, glucose uptake is mediated by the glucose transporter type 1 (GluT1). GluT1 deficiency or mutations cause severe physiological disorders. GluT1 is also an important target in cancer therapy as it is overexpressed in tumor cells. Previous studies have suggested that GluT1 mediates solute transfer through a cycle of conformational changes. However, the corresponding 3D structures adopted by the transporter during the transfer process remain elusive. In the present work, we first elucidate the whole conformational landscape of GluT1 in the absence of glucose, using long molecular dynamics simulations and show that the transitions can be accomplished through thermal fluctuations. Importantly, we highlight a strong coupling between intracellular and extracellular domains of the protein that contributes to the transmembrane helices reorientation during the transition. The conformations adopted during the simulations differ from the known 3D bacterial homologs structures resolved in similar states. In holo state simulations, we find that glucose transits along the pathway through significant rotational motions, while maintaining hydrogen bonds with the protein. These persistent motions affect side chains orientation, which impacts protein mechanics and allows glucose progression.

Diagnostic Challenges Associated with GLUT1 Deficiency: Phenotypic Variabilities and Evolving Clinical Features.

GLUT1 deficiency is a rare neurometabolic disorder that can be effectively treated with ketogenic diet. However, this condition is underdiagnosed due to its nonspecific, overlapping, and evolving symptoms with age. We retrospectively reviewed the clinical course of nine patients diagnosed with GLUT1 deficiency, based on SLC2A1 mutations and/or glucose concentration in cerebrospinal fluid. The patients included eight boys and one girl who initially presented with seizures (44%, 4/9) or delayed development (44%, 4/9) before 2 years of age, except for one patient who presented with apnea as a neonate. Over the clinical course, all of the children developed seizures of the mixed type, including absence seizures and generalized tonic–clonic seizures. About half (56%, 5/9) showed movement disorders such as ataxia, dystonia, or dyskinesia. We observed an evolution of phenotype over time, although this was not uniform across all patients. Only one child had microcephaly. In five patients, ketogenic diet was effective in reducing seizures and movement symptoms, and the patients exhibited subjective improvement in cognitive function. Diagnosing GLUT1 deficiency can be challenging due to the phenotypic variability and evolution. A high index of clinical suspicion in pediatric and even older patients with epilepsy or movement disorders is key to the early diagnosis and treatment, which can improve the patient's quality of life.

GLUT1 deficiency syndrome: A case report with a novel SLC2A1 mutation

Introduction. GLUT1 deficiency syndrome (GLUT1 DS, OMIM 606777) is a metabolic brain disorder caused by mutations in SLC2A1 gene (chromosome 1) encoding glucose transporter type 1 located on blood-brain membrane. The ?classic? phenotype in children includes early onset generalized farmacoresistant epilepsy, developmental delay, complex movement disorders and acquired microcephaly. However, there are milder phenotypes without epilepsy which could be seen in older children. The ketogenic diet is a treatment of choice. Case report. We present a four-yearold female patient with farmacoresistant generalized epilepsy, paroxysmal dystonic posturing, ataxia, hypotonia, developmental delay (motor, attention and speech disturbances), and microcephaly. The genetic testing revealed a novel point mutation at c.156T &gt; A (p.Y52X) in exon 3 of SLC2A1 gene. The patient responded excellent on ketogenic diet. Conclusion. GLUT1 DS is treatable, and likely to be under-diagnosed neurological disorder. The ketogenic diet is resulting in good control of seizures in the patients, and it has certain benefit for the neurodevelopmental disability.

Glucose transporter type 1 deficiency syndrome (GLUT1-DS) – delayed diagnosis and treatment. A case report

Glucose transporter type 1 deficiency syndrome (GLUT1-DS) – delayed diagnosis and treatment. A case report

Study of de novo point mutations in known genes among patients with unexplained intellectual disability or developmental delay

Objective: To analyze the de novo point mutations in known genes among patients with unexplained intellectual disability (ID) or developmental retardation (DD). Methods: A total of 120 outpatients with ID or DD were recruited in the Department of Neurology, Affiliated Children's Hospital of Capital Institute of Pediatrics between September 2015 and April 2017. Target gene sequencing was used to screen the candidate gene. The sequencing data were analyzed by a variety of bioinformatics software. Combining with the phenotypes of the patients, the candidate genetic/genomic variants were identified from next-generation sequencing data. The final pathogenicity of the genetic/genomic variants were interpreted according to the guideline of the American College of Medical Genetics and Genomics (ACMG) for variants after segregation analysis in the parents and necessary family members by Sanger sequencing. The comprehensive physiological function and signaling pathways of 20 disease genes with de novo point mutation discovery was also studied. Results: Among the 120 patients, 23 patients were found to carry clear pathological changes, and the incidence of de novo point variation was 19.2%. The patients included 12 males and 11 females, with an age of 2 months to 6-year-6-month. Five patients were diagnosed with early onset of epileptic encephalopathy. Seven had mental retardation type 5, 6, 8, 19, 20, 22, 39, respectively. Weill-Marchesani syndrome type 2 was found in one case, Wiedemann-Steiner syndrome in one case, Coffin-Siris syndrome in two cases, Rubinstein-Taybi syndrome in one case, GLUT1 deficiency syndrome in one case, Rett syndrome in one case, cardio-facio-cutaneous syndrome 3 in one case, neurodegeneration with brain iron accumulation in one case, corpus callosum local dysplasia in one case, and congenital fibrosis of the extra-ocular muscles in one case. A total of 20 novel mutations were reported in this study. No somatic mutation was found in the samples of 6 patients with mutation and their parents' peripheral blood DNA samples by amplicon-based deep sequencing. This study found that the main disease genes were involved in chromatin remodeling, transcriptional regulation, autophagy body assembly, MAPK signal pathway, DNA methylation, potassium, sodium ion transport, cell skeleton assembly and skeletal muscle development. These genes were significantly enriched in the following biological processes: Ras signaling pathways, transcription factor binding and cancer related signaling pathway. Conclusions: The etiology of children affected with intellectual disability or developmental delay is complex. Harmful de novo point mutation plays an important role in these diseases. Targeted exome/genome sequencing based on the core family is helpful for the molecular diagnosis of patients and the discovery of more genes.

Cardiovascular Risks of Ketogenic Diet for Glut-1 Deficiency.

Investigators from Children's Hospitals of Aschaffenburg-Alzenau, Germany, and Essen University, Germany reported on long-term cardiovascular risks of ketogenic diet (KD) treatment for Glut1 Deficiency syndrome (GLUT1-DS).

Mutations in Disordered Regions Can Cause Disease by Creating Dileucine Motifs

Many disease-causing missense mutations affect intrinsically disordered regions (IDRs) of proteins, but the molecular mechanism of their pathogenicity is enigmatic. Here, we employ a peptide-based proteomic screen to investigate the impact of mutations in IDRs on protein-protein interactions. We find thatmutations in disordered cytosolic regions of three transmembrane proteins (GLUT1, ITPR1, and CACNA1H) lead to an increased clathrin binding. All three mutations create dileucine motifs known to mediate clathrin-dependent trafficking. Follow-up experiments on GLUT1 (SLC2A1), the glucose transporter causative of GLUT1 deficiency syndrome, revealed that the mutated protein mislocalizes to intracellular compartments. Mutant GLUT1 interacts with adaptor proteins (APs) invitro, and knocking down AP-2 reverts the cellular mislocalization and restores glucose transport. A systematic analysis of other known disease-causing variants revealed a significant and specific overrepresentation of gained dileucine motifs in structurally disordered cytosolic domains of transmembrane proteins. Thus, several mutations in disordered regions appear to cause "dileucineopathies."