Phenotype variability of GLUT1 deficiency syndrome: Description of a case series with novel SLC2A1 gene mutations

Glucose transporter type 1 (GLUT1) deficiency due to SLC2A1 mutations causes a wide spectrum of neurologic disorders ranging from severe encephalopathy with developmental delay, epilepsy, ataxia, and acquired microcephaly to atypical less severe variants. Early diagnosis is crucial for prompt initiation of a ketogenic diet. Recognizing GLUT1 deficiency syndrome (GLUT1DS) may be challenging and results in delayed diagnosis. Here we describe the clinical and molecular findings of patients with SLC2A1 mutations referred to our adult Epilepsy Center. Patients with a clinical history suggestive of GLUT1DS were screened for SLC2A1 mutations. Blood samples were collected from probands and first-degree relatives. A lumbar puncture was performed in two patients in fasting state, and cerebrospinal fluid and blood glucose measurement were undertaken at the same time. Since 2010, 19 GLUT1DS probands have been screened for SLC2A1 mutations. We identified four different SLC2A1 mutations in three sporadic cases and one family. Three mutations (c.130_135delTACAAC, c.342_343insA, and c.845A > G) were novel, whereas one was previously reported in the literature associated with a different phenotype (c.497_499delTCG). Here we describe a small case series of patients with sporadic and familial GLUT1DS presenting with a broad phenotypic heterogeneity which is likely to be responsible for the considerable delay in diagnosis.