TBC1D24-related familial infantile multifocal myoclonus: Description of a new Chinese pedigree with a 20 year follow up

Disorders associated with mutations in the Tre2/Bub2/Cdc16 (TBC)1 domain family member 24 gene (TBC1D24) present a wide range of phenotypes, ranging from mild to fatal seizure diseases, non-syndromic deafness, and complex syndromes such as deafness, onychodystrophy, osteodystrophy, and mental retardation(DOOR syndrome). In this study, we introduce three siblings of a previously unreported Chinese family with familial infantile myoclonic epilepsy caused by a homozygous TBC1D24 mutation. Genomic DNA was extracted from whole blood of the proband, his parents, and sisters. TBC1D24 exomes were sequenced by whole exome sequencing then analyzed by genetic analysis with Sanger sequencing validation. The patients were followed up for more than 20 years to summarize their clinical features. Genetic analysis identified a homozygous TBC1D24 mutation (c.241_252del12) in the proband and his sisters. Prediction models suggest that the mutation leads to an alteration in the properties and structure of the TBC1D24 protein, especially in the folding direction of the loop region, which is likely to decrease protein activity. The patients manifested with early-onset myoclonic epilepsy, were prone to status epilepticus, and seizures only occurred during wakefulness. Imaging characteristics included cerebellar atrophy and abnormal cerebellar signals. We report a pedigree case of infantile myoclonic epilepsy caused by a homozygous TBC1D24 mutation. Our long-term clinical follow-up not only enriches the clinical phenotype of the disease, but also provides a clinical experience for the early diagnosis and clinical treatment of the disease.