Abstract:This article reports the clinical and genetic features of a case of Tatton-Brown-Rahman syndrome (TBRS) caused by DNMT3A gene mutation. A girl, aged 8 months and 14 days, had the clinical manifestations of psychomotor retardation, hypotonia, ventricular enlargement, and tonsillar hernia malformation. Gene analysis identified a novel heterozygous mutation, c.134C > T(p.A45V), in the DNMT3A gene, and the wild type was observed at this locus in her parents. This mutation was determined as a possible pathogenic mutation according to the guidelines of American College of Medical Genetics and Genomics, which had not been reported in previous studies and conformed to autosomal dominant inheritance. This child was diagnosed with TBRS. TBRS often has a good prognosis, with overgrowth and mental retardation as the most common clinical manifestations, and behavioral and psychiatric problems, scoliosis, and afebrile seizures are possible complications of TBRS. The possibility of TBRS should be considered for children with overgrowth and mental retardation, and genetic diagnosis should be conducted when necessary.