Clinical and Genetic Characteristics of Chinese Children With GLUT1 Deficiency Syndrome: Case Report and Literature Review

Objective: GLUT1 deficiency syndrome (GLUT1-DS) is a rare, treatable neurometabolic disorder. However, its diagnosis may be challenging due to the various and evolving phenotypes. Here we report the first Chinese familial cases with genetically confirmed GLUT1-DS and analyze the characteristics of Chinese children with GLUT1-DS from clinical, laboratory, and genetic aspects.Methods: We reported a Chinese family with three members affected with GLUT1-DS and searched for relevant articles up to September 2020 from PubMed, WOS, CNKI, and WanFang databases. A total of 30 Chinese patients diagnosed with GLUT1-DS (three newly identified patients in one family and 27 previously reported ones) were included and analyzed in this study.Results: The median age of onset of the 30 patients (male: 18, female: 12) was 8.5 months (range, 33 days to 10 years). Epileptic seizures were found in 25 patients, most with generalized tonic–clonic and focal ones. Movement disorders were found in 20 patients—frequently with ataxia and dystonia, developmental delay in 25 patients, and microcephaly only in six patients. The cerebrospinal fluid (CSF) analysis showed decreased CSF glucose (median: 1.63 mmol/L, range: 1.1–2.6 mmol/L) and glucose ratio of CSF to blood (median: 0.340; range: 0.215–0.484). The genetic testing performed in 28 patients revealed 27 cases with pathogenic variations of the SLC2A1 gene, including 10 missense, nine frameshift, three nonsense, three large fragment deletions, and two splice-site mutations. Most patients had a good response to the treatment of ketogenic diet or regular diet with increased frequency. Although three patients in this Chinese family carried the same pathogenic mutation c.73C > T (p.Q25X) in the SLC2A1 gene, their symptoms and responses to treatment were not exactly the same.Conclusion: The clinical manifestations of GLUT1-DS are heterogeneous, even among family members sharing the same mutation. For children with unexplained epileptic seizures, developmental delay, and complex movement disorders, detection of low CSF glucose or SLC2A1 gene mutations is helpful for the diagnosis of GLUT1-DS. Early initiation of ketogenic diet treatment significantly improves the symptoms and prognosis of GLUT1-DS.

Case Report: The Association of Wilson Disease in a Patient With Ataxia and GLUT-1 Deficiency

Background: Wilson disease (WD) and glucose transporter type 1 (GLUT1) deficiency syndrome are two syndromes with different modes of inheritance but share certain similarities on neurological presentation. To date we have not found previous reports of an association between these two disorders.Case Presentation: Here we describe a 9-year-old male with global developmental delay that presented with intermittent and sudden onset weakness that first occurred at age 3. He was diagnosed with a mutation in the SLC2A1 (Solute Carrier Family 2 Member 1) gene, which results in GLUT1 deficiency. A ketogenic diet could not be started because of unexplained elevated liver enzymes. Due to his liver enzymes' persistent elevation, further investigations demonstrated mildly decreased ceruloplasmin levels, high basal 24-h urinary copper excretion, and an elevated hepatic parenchymal copper concentration on liver biopsy, consistent with WD. Genetic testing revealed two separate mutations in the ATP7B (ATPase Copper Transporting Beta) gene, consistent with WD. The patient was treated with a low copper diet, zinc acetate, and trientine hydrochloride. When liver enzymes normalized, he was subsequently started on a ketogenic diet with improvement in neurological symptoms. His neurological symptoms were most likely secondary to GLUT1 deficiency syndrome, as WD's neurological symptoms are primarily observed in the second decade of life.Conclusion: Recent studies have demonstrated the importance of genetic testing upon unexplained persistent elevation of liver enzymes. This case highlights the importance of carefully evaluating a patient with an unexplained liver disorder, even in the presence of primary neurological disease, as it can have significant therapeutic implications.

GLUT1 Deficiency Syndrome—Early Treatment Maintains Cognitive Development? (Literature Review and Case Report)

Glucose transporter type 1 (GLUT1) is the most important energy carrier of the brain across the blood–brain barrier, and a genetic defect of GLUT1 is known as GLUT1 deficiency syndrome (GLUT1DS). It is characterized by early infantile seizures, developmental delay, microcephaly, ataxia, and various paroxysmal neurological phenomena. In most cases, GLUT1DS is caused by heterozygous single-nucleotide variants (SNVs) in the SLC2A1 gene that provoke complete or severe impairment of the functionality and/or expression of GLUT1 in the brain. Despite the rarity of these diseases, GLUT1DS is of high clinical interest since a very effective therapy, the ketogenic diet, can improve or reverse symptoms, especially if it is started as early as possible. We present a clinical phenotype, biochemical analysis, electroencephalographic and neuropsychological features of an 11-month-old boy with myoclonic seizures, hypogammaglobulinemia, and mildly impaired gross motor development. Using sequence analysis and deletion/duplication testing, deletion of an entire coding sequence in the SLC2A1 gene was detected. Early introduction of a modified Atkins diet maintained a seizure-free period without antiseizure medications and normal cognitive development in the follow-up period. Our report summarizes the clinical features of GLUT1 syndromes and discusses the importance of early identification and molecular confirmation of GLUT1DS as a treatable metabolic disorder.

Deletion of Glut1 in early postnatal cartilage reprograms chondrocytes toward enhanced glutamine oxidation

Glucose metabolism is fundamental for the functions of all tissues, including cartilage. Despite the emerging evidence related to glucose metabolism in the regulation of prenatal cartilage development, little is known about the role of glucose metabolism and its biochemical basis in postnatal cartilage growth and homeostasis. We show here that genetic deletion of the glucose transporter Glut1 in postnatal cartilage impairs cell proliferation and matrix production in growth plate (GPs) but paradoxically increases cartilage remnants in the metaphysis, resulting in shortening of long bones. On the other hand, articular cartilage (AC) with Glut1 deficiency presents diminished cellularity and loss of proteoglycans, which ultimately progress to cartilage fibrosis. Moreover, predisposition to Glut1 deficiency severely exacerbates injury-induced osteoarthritis. Regardless of the disparities in glucose metabolism between GP and AC chondrocytes under normal conditions, both types of chondrocytes demonstrate metabolic plasticity to enhance glutamine utilization and oxidation in the absence of glucose availability. However, uncontrolled glutamine flux causes collagen overmodification, thus affecting extracellular matrix remodeling in both cartilage compartments. These results uncover the pivotal and distinct roles of Glut1-mediated glucose metabolism in two of the postnatal cartilage compartments and link some cartilage abnormalities to altered glucose/glutamine metabolism.

Re-analysis of whole-exome sequencing data reveals a novel splicing variant in the SLC2A1 in a patient with GLUT1 Deficiency Syndrome 1 accompanied by hemangioma: a case report

Background GLUT1 Deficiency Syndrome 1 (GLUT1DS1) is a neurological disorder caused by either heterozygous or homozygous mutations in the Solute Carrier Family 2, Member 1 (SLC2A1) gene. SLC2A1 encodes Glucose transporter type 1 (GLUT1) protein, which is the primary glucose transporter at the blood–brain barrier. A ketogenic diet (KD) provides an alternative fuel for brain metabolism to treat impaired glucose transport. By reanalyzing exome data, we identified a de novo heterozygous SLC2A1 variant in a girl with epilepsy. After reversed phenotyping with neurometabolic tests, she was diagnosed with GLUT1DS1 and started on a KD. The patient's symptoms responded to the diet. Here, we report a patient with GLUT1DS1 with a novel SLC2A1 mutation. She also has a hemangioma which has not been reported in association with this syndrome before. Case presentation A 5-year 8-month girl with global developmental delay, spasticity, intellectual disability, dysarthric speech, abnormal eye movements, and hemangioma. The electroencephalography (EEG) result revealed that she had epilepsy. Magnetic resonance imaging (MRI) showed that non-specific white matter abnormalities. Whole Exome Sequencing (WES) was previously performed, but the case remained unsolved. The re-analysis of WES data revealed a heterozygous splicing variant in the SLC2A1 gene. Segregation analysis with parental DNA samples indicated that the variant occurred de novo. Lumbar puncture (LP) confirmed the diagnosis, and the patient started on a KD. Her seizures responded to the KD. She has been seizure-free since shortly after the initiation of the diet. She also had decreased involuntary movements, her speech became more understandable, and her vocabulary increased after the diet. Conclusions We identified a novel de novo variant in the SLC2A1 gene in a patient who previously had a negative WES result. The patient has been diagnosed with GLUT1DS1. The syndrome is a treatable condition, but the differential diagnosis is not an easy process due to showing a wide range of phenotypic spectrum and the overlapping symptoms with other neurological diseases. The diagnosis necessitates a genomic testing approach. Our findings also highlight the importance of re-analysis to undiagnosed cases after initial WES to reveal disease-causing variants.

Continuous Glucose Monitoring Facilitates Diazoxide Use in the Management of Glut1 Deficiency Syndrome

Background: Glut1 deficiency syndrome (Glut1DS) is caused by mutations in SLC2A1 on chromosome 1p34.2, which impairs transmembrane glucose transport across the blood brain barrier resulting in hypoglycorrhachia and decreased glucose availability for brain metabolism. This causes a drug-resistant, metabolic epilepsy due to energy deficiency. Standard treatment for Glut1DS is the ketogenic diet (KD) but treatment options are limited if patients fail the KD. Diazoxide, which inhibits insulin release, was used sparingly in the past for a few Glut1DS patients to increase blood glucose levels and thus intracerebral glucose levels. Unfortunately, their treatment was complicated by unacceptable persistent hyperglycemia with blood glucoses in the 300s to 500s. We investigated the use of a continuous glucose monitor (CGM) to enable titration of diazoxide therapy in a patient with KD-resistant Glut1DS. Clinical Case: A 14-year-old girl with Glut1DS (c.398_399delGCinsTT:p.Lys133Phe) failed the KD due to severe nausea, vomiting, abdominal pain, and hypertriglyceridemia. Laboratory tests revealed CSF glucose of 36 mg/dL when blood glucose was 93 mg/dL. Over the course of 3 hospitalizations targeting blood glucose levels in the range of 120-180 mg/dL with diazoxide, EEG seizure activity decreased from 3 to 0 absence seizures per hour. CGM placement during the third hospitalization showed an average interstitial glucose of 157 mg/dL with glucose variability of 20.8% on diazoxide dose of 7.3 mg/kg/day. After discharge, CGM has been used to adjust diazoxide doses 2-4 times a week to achieve target interstitial glucoses of 140-180 mg/dL. Repeat laboratory tests revealed CSF glucose of 55 mg/dL when interstitial glucose was 158 mg/dL. Current diazoxide dose is 7.9 mg/kg/day and most recent hemoglobin A1c was 5.4%. Conclusions: This is the first report demonstrating CGM as a tool facilitating the safe initiation and real-time titration of diazoxide in Glut1DS patients who have failed the KD. Diazoxide addresses neuroglycopenia more physiologically by raising blood glucose levels and subsequently intracerebral glucose levels. CGM allows for more accurate titration of blood glucose with diazoxide while avoiding complications of hyperglycemia and thus introduces the possibility of diazoxide becoming a standard of care for Glut1DS. More broadly, CGM provides a valuable tool for the management of other disorders of glucose transport and carbohydrate metabolism.

Classic Ketogenic Diet and Modified Atkins Diet in SLC2A1 Positive and Negative Patients with Suspected GLUT1 Deficiency Syndrome: A Single Center Analysis of 18 Cases

Background: Glucose transporter type 1 deficiency syndrome (GLUT1DS) is caused by mutations in the SLC2A1 gene and produces seizures, neurodevelopmental impairment, and movement disorders. Ketogenic dietary therapies (KDT) are the gold standard treatment. Similar symptoms may appear in SLC2A1 negative patients. The purpose is to evaluate the effectiveness of KDT in children with GLUT1DS suspected SLC2A1 (+) and (-), side effects (SE), and the impact on patients nutritional status. Methods: An observational descriptive study was conducted to describe 18 children (January 2009–August 2020). SLC2A1 analysis, seizures, movement disorder, anti-epileptic drugs (AEDS), anthropometry, SE, and laboratory assessment were monitored baseline and at 3, 6, 12, and 24 months after the onset of KDT. Results: 6/18 were SLC2A1(+) and 13/18 had seizures. In these groups, the age for debut of symptoms was higher. The mean time from debut to KDT onset was higher in SLC2A1(+). The modified Atkins diet (MAD) was used in 12 (5 SLC2A1(+)). Movement disorder improved (4/5), and a reduction in seizures >50% compared to baseline was achieved in more than half of the epileptic children throughout the follow-up. No differences in effectiveness were found according to the type of KDT. Early SE occurred in 33%. Long-term SE occurred in 10, 5, 7, and 5 children throughout the follow-up. The most frequent SE were constipation, hypercalciuria, and hyperlipidaemia. No differences in growth were found according to the SLC2A1 mutation or type of KDT. Conclusions: CKD and MAD were effective for SLC2A1 positive and negative patients in our cohort. SE were frequent, but mild. Permanent monitoring should be made to identify SE and nutritional deficits.