OBJECTIVE: To elucidate the clinical and genetic characteristics of familial cases with Glucose transporter type 1 deficiency syndrome (Glut1DS). METHODS: A survey of family history was conducted on children (proband) with Glut1DS who had visited Peking University First Hospital between November 2008 and April 2024 by focusing on the clinical manifestations of family members. Peripheral venous blood (2 mL) was collected from the pediatric patients and their parents. Genomic DNA was extracted and sequenced subsequently. Sanger sequencing was performed to validate the identified variant sites of the SLC2A1 gene in the probands and their family members. The pathogenicity of suspected variants was analyzed according to the 2015 American College of Medical Genetics and Genomics (ACMG) Standards and Guidelines for the Interpretation of Sequence Variants. The clinical features, auxiliary examinations, and mutational characteristics of family members with SLC2A1 variants were analyzed. This study has been approved by the Clinical Research Ethics Committee of Peking University First Hospital (Ethics No. 2021 Research 332). RESULTS: Among 87 cases with Glut1DS, 10 families with autosomal dominate inherited cases were identified, accounting for 11.0% of the cases. Of the 11 children, 8 were boys and 3 were girls. The onset of the disease had ranged from 3 months to 120 months (median 6 months), with 4 cases of early-onset classic type, 2 cases of late-onset classic type, and 5 cases of non-classic type. Six children had seizures, and 7 exhibited movement disorders. Seven children underwent developmental assessment, of which 3 had mild developmental delay, 2 were borderline, and 2 were normal. Nine children underwent lumbar puncture. The cerebrospinal fluid glucose levels ranged from 1.45 to 2.25 mmol/L (median 1.86 mmol/L), and the cerebrospinal fluid to blood glucose ratios ranged from 0.29 to 0.44 (median 0.35). Among the 8 fathers with SLC2A1 gene variants, 4 were asymptomatic, 2 developed paroxysmal exercise-induced movement disorders (PED) in childhood and adulthood, respectively. 1 had poor memory since childhood, 1 developed migraines during adolescence, and his sister was an asymptomatic carrier. The father with childhood-onset PED had a cerebrospinal fluid test with CSF glucose of 1.85 mmol/L. Of the 3 mothers with SLC2A1 gene mutations, 1 was an asymptomatic carrier; 2 developed PED in childhood and after the age of 20, respectively. The mother who developed PED in childhood also had psychomotor developmental delay. Genetic testing results revealed that among 10 families, 8 carried missense variants, 1 carried a nonsense variant, and 1 carried a small fragment insertion leading to a frameshift variant. Among the 11 cases, SLC2A1 gene variants in 8 children were inherited from their fathers, while in 3 cases, the variants were inherited from their mothers. The pathogenicity of the genetic variants was evaluated according to the Standards and Guidelines for the Interpretation of Sequence Variants published by the ACMG. Among the 8 variants identified in the 10 families, 4 were classified as pathogenic variants, 1 as likely pathogenic, and 3 as variants of uncertain significance (VUS). Four variant sites, including c.204_205insTCTC (p.V69fs), c.412G>C (p.G138R), c.431T>G (p.V144G), and c.875A>G (p.Y292C), were not previously reported in the literature. Among these, the latter three were categorized as VUS. CONCLUSION: Familial Glut1DS account for 11.0% of the cases in China, with the majority of SLC2A1 gene variants inherited from the fathers, predominantly missense mutations, and with an autosomal dominant inheritance pattern. Probands tend to have earlier onset and more severe symptoms than their parents, who often present with mild or no symptoms.