Glucose transporter type 1 deficiency syndrome (Glut1DS) is a treatable genetic neurometabolic disorder because of a variant in the Glut1 transporter, encoded by the SLC2A1 gene (OMIM*138140), resulting in impaired glucose transport across the blood–brain barrier. Glut1DS was initially reported in infants with progressive encephalopathy, acquired microcephaly, and drug‐resistant epilepsy and can be treated with the ketogenic diet. 1 With increased awareness and progress in diagnosis, the phenotype has expanded to include milder presentations of epilepsy, movement disorders, and cognitive impairment. 2 Glut1DS is estimated to affect 1 in every 24,000 live births. 3
Case Report
A 5‐year‐old Spanish girl presented with paroxysmal movement disorder, characterized by abnormal leg posture, unsteady gait, and frequent falls by 2 years and 8 months of age. Five months later, she had an episode that lasted 4 hours. Subsequently, frequent episodes were reported to occur on a weekly basis. One of those episodes included dysarthria without loss of consciousness (Video 1). Given her age, her family has been unable to identify a specific trigger for these episodes. She was born to term after a normal pregnancy to healthy non‐consanguineous Caucasian parents with a positive family history of epilepsy (maternal grandmother). Her early neurodevelopment was described as normal, with a slight delay in independent gait acquisition at 18 months. A neurological examination at 5 years and 7 months of age showed microcephaly (cranial circumference of 48 cm, 2nd percentile); although no other neurological signs were observed. During hospitalization, a brain MRI was performed with normal results. Video electroencephalogram (EEG) showed electroclinical myoclonic seizures. These epileptic myoclonus occurred infrequently and were not identified by the family as seizures. She had no other types of seizures. Extensive biochemical and metabolic tests showed normal results. Lumbar puncture showed hypoglycorrhachia of 32 mg/dL and a cerebrospinal fluid (CSF)/serum glucose ratio of 0.5 (reference value >0.60) and flow cytometric analysis of the surface expression of Glut1 in circulating erythrocytes was reduced to 36% compared to the general population according to the METAglut1 test (Fig. 1). Both tests were helpful in confirming the diagnostic suspicion of Glut1DS. Following that, whole exome sequencing revealed a previously reported heterozygous de novo variant on the SLC2A1 gene, p.Arg333Gln/c.998G>A. A ketogenic diet with a fat‐to‐protein plus carbohydrate ratio of 4:1 was started with good tolerance. In clinical follow‐up after 24 months of ketogenic diet treatment, no further episodes of paroxysmal movement disorder or myoclonic seizures were reported. The video EEG did not report any epileptic abnormalities or seizures. Her neuropsychological evaluation is described in Appendix S1. The legal guardians gave their consent for publication and the study was approved by the Ethics Committee (ART‐07‐21).
Video 1.
Segment 1: inter‐episode normal gait. Segment 2: paroxysmal episode characterized by dyskinetic movements and dystonic postures involving the legs. Segment 3: paroxysmal episode characterized by dyskinetic movements leading to a fall and difficulties maintaining an erect posture induced by exertion. Segment 4: an episode of myoclonus causes the patient to fall while sitting. Segment 1 to 5 was recorded before the ketogenic diet was started. Segment 5: normal movements while on a ketogenic diet. Segment 2 and 3 showed the previously described “criss‐cross gait” pattern of Glut1‐DS patients. 8
FIG. 1.
Shows the Glut1 expression level as determined by the METAglut1 test. Box plots were drawn using data from a series of 30 Glut1DS patients published in Gras et al. 6 As control, more than 300 blood donors were used. The patient's residual Glut1 expression on erythrocytes is shown (box plots show percentiles 5th, 25th, 75th, and 95th, and the mean).
Discussion
Glut1DS is a well‐known clinical entity comprising a classical (90%) and a non‐classical (10%) phenotype. Non‐epileptic paroxysmal events, such as those presented by our patient, have been detected in 28% of a series of 57 patients with Glut1DS. 4 Although paroxysmal exercise‐induced dyskinesia is the most common type of paroxysmal dyskinesia in Glut1DS, other non‐kinesigenic dyskinesia, episodic ataxia, or a combination of subtypes can also be present (Video 1). 5
The diagnosis of Glut1DS is established with a CSF glucose concentration of <60 mg/dL in combination with a normal blood glucose concentration and with the identification of a heterozygous pathogenic variant in the SLC2A1 gene by molecular genetic testing. However, the decrease of more than 20% in Glut1 expression on the surface of the erythrocytes detected by the METAglut1 test compared to the general population is also highly suggestive. 6
Gras et al, 6 first introduced the METAglut1 as a simple diagnostic blood test for Glut1DS using flow cytometry, with a detection rate of 78% in patients with proven Glut1DS. An EDTA tube is used to obtain whole blood for the METAglut1 test. The patient does not need to fast before the blood draw. The sample is sent to the central lab at 4°C and results are available in 48 hours. The assay takes approximately 1 hour to run and analyze 1 to 18 samples. Glut1 expression is measured directly on erythrocytes using a simple flow cytometer. 6 Currently, the test is only available in France but it is expected to be implemented soon in a number of European countries with the CE mark (Spain, Italy, and Germany).
The fact that METAglut1 can be performed using blood analysis rather than a lumbar puncture and that it takes only a short time to perform compared to months for a genetic study in a hospital setting, clearly demonstrates its use in screening for Glut1DS. The latest international Glut1DS study group review concluded that the METAglut1 test is not yet a standard diagnostic tool for Glut1DS, 7 whereas ongoing studies should provide actionable results soon (NCT 03722212).
In conclusion, our report describes a case of non‐kinesigenic paroxysmal dyskinesias associated with Glut1DS and highlights METAglut1 test use for rapid disease diagnosis.
Author Roles
(1) Research project: A. Conception, B. Organization, C. Execution; (2) Statistical Analysis: A. Design, B. Execution, C. Review and Critique; (3) Manuscript: A. Writing of the First Draft, B. Review and Critique.
L.S.: 3A, 3B
L.M.: 1C, 3B
D.Y.: 1C, 3B
C.V.: 1C, 3B
V.P.: 1C, 2A, 3B
J.D.O.E.: 1A, 1B, 1C, 3B
Disclosures
Ethical Compliance Statement
The legal guardians gave their written consent to the recording of the patient for publication, and the study received ethical approval by the Ethics Committee (ART‐07‐21). We confirm that we have read the Journal's position on issues involved in ethical publication and affirm that this work is consistent with those guidelines.
Funding Sources and Conflicts of Interest
No specific funding was received for this work. V.P. is the cofounder and CEO of Metafora Biosystems. The authors declare that there are no other conflicts of interest relevant to this work.
Financial Disclosures for the Previous 12 Months
The authors declare that there are no additional disclosures to report.
Supporting information
Appendix S1. Neuropsychological evaluation. (A) Kaufman K‐BIT Brief Intelligence Test. The global composite IQ score is 94, placing the intellectual capabilities of the patient at a medium level rather than the expected level for her age. (B) Vineland‐II Interview. The patient achieves appropriate sociability scores, but deviates from normal communication, daily skills, and psychomotor development. (C) Navarra oral language test (PLON). The PLON results suggest that the linguistic content and use are within normal limits. The findings of the language form section demonstrate that certain features of morphology and syntax do not develop with age.
Acknowledgments
The authors thank the patient and her family.
References
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Supplementary Materials
Appendix S1. Neuropsychological evaluation. (A) Kaufman K‐BIT Brief Intelligence Test. The global composite IQ score is 94, placing the intellectual capabilities of the patient at a medium level rather than the expected level for her age. (B) Vineland‐II Interview. The patient achieves appropriate sociability scores, but deviates from normal communication, daily skills, and psychomotor development. (C) Navarra oral language test (PLON). The PLON results suggest that the linguistic content and use are within normal limits. The findings of the language form section demonstrate that certain features of morphology and syntax do not develop with age.