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

OBJECTIVE To investigate the clinical and genetic features of a Chinese girl featuring mental retardation, intellectual disability, language development delay and epilepsy. METHODS 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. RESULTS 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. CONCLUSION 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.