Objective: To describe the spectrum of phenotypes in children and adolescents with biochemically and/or genetically proven Glucose Transporter 1 (GLUT1) deficiency.

Background: The phenotypes in GLUT1 deficiency include classic (developmental delay, infantile onset seizures, movement disorders, acquired microcephaly), carbohydrate responsive phenotype (symptoms improving after carbohydrate intake), movement disorder without seizures and paroxysmal exercise induced dyskinesias and epilepsy.¹  As there is paucity of studies on the spectrum of movement disorders and expanding clinical phenotypes from different ethnic background, we aimed to study the phenotypic spectrum and movement disorders in children and adolescents with biochemically and/or genetically proven GLUT1 deficiency from multiple centers across the globe.

Method: This retrospective study included children and adolescents aged ≤18 years with a biochemical diagnosis of GLUT1 deficiency as identified by fasting CSF glucose less than 60 mg/dL (<3.3 mmol/L) and a normal blood sugar level and/or confirmed genetic diagnosis.^2,3 The clinical, laboratory, and neurophysiology findings and gene variant details were collected from centers in Canada, Chile and India. More centers from United States, Europe, Middle East, Sri Lanka, and Australia are being recruited into this study.

Results: Among an anticipated enrolment of more than 100 patients, preliminary data analysis of 58 patients was done. No sex predilection was identified (male:female ratio- 1.1:1). Four families had more than one affected child. The mean age at presentation was 52.6 months. Developmental delay (90%), epilepsy (80%) and movement disorders (45%) were identified in this cohort. The spectrum of movement disorders includes dystonia (30%), Parkinsonism (22%), ataxia (19%), tremor (15%), and chorea (10%). Paroxysmal dyskinesias were observed in about 15% individuals. Other observed clinical features include autism, behavioral disturbances, seizures, microcephaly, tone abnormalities, recurrent motor weakness and hemiplegic migraine. Variable clinical response was observed on treatment with dietary therapies.

Conclusion: The phenotypic spectrum in patients with GLUT1 deficiency is often diverse and non-paroxysmal movement disorders represent one of the commonest manifestations.

References: 1. Brockmann K. The expanding phenotype of GLUT1-deficiency syndrome. Brain Dev. 2009 Aug;31(7):545-52. doi: 10.1016/j.braindev.2009.02.008. Epub 2009 Mar 21. PMID: 19304421.
2. Wang D, Sands T, Tang M, et al. Glucose Transporter Type 1 Deficiency Syndrome. 2002 Jul 30 [Updated 2025 Mar 6]. In: Adam MP, Feldman J, Mirzaa GM, et al., editors. GeneReviews® [Internet]. Seattle (WA): University of Washington, Seattle; 1993-2025. Available from: https://www.ncbi.nlm.nih.gov/books/NBK1430/
3. Leen WG, Wevers RA, Kamsteeg EJ, Scheffer H, Verbeek MM, Willemsen MA. Cerebrospinal fluid analysis in the workup of GLUT1 deficiency syndrome: a systematic review. JAMA Neurol. 2013 Nov;70(11):1440-4. doi: 10.1001/jamaneurol.2013.3090. PMID: 23999624.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/phenotypic-spectrum-in-children-and-adolescents-with-glucose-transporter-1-deficiency-a-multicentric-retrospective-study/