[A case with autosomal dominant mental retardation type 5 due to de novo SYNGAP1 variant].

To investigate the clinical and genetic features of a Chinese girl featuring mental retardation, intellectual disability, language development delay and epilepsy.G-banded chromosomal karyotyping was carried out for the child. Genomic DNA of the patient and her parents was extracted and subjected to high-throughput sequencing. The results were analyzed with bioinformatic tools and validated by Sanger sequencing.The karyotype of the child was ascertained as 46,XX. Sequencing result showed that she has carried a de novo heterozygous c.1861C>T (p.R621X) variant of the SYNGAP1 gene.The nonsense variant c.1861C>T (p.R621X) of the SYNGAP1 gene probably underlies the disease in this child. Above result has enabled genetic diagnosis and counseling for her family.