Diagnosis of a case with mental retardation due to novel compound heterozygous variants of TRAPPC9 gene

Objective To explore the genetic basis for a boy with mental retardation. Methods Clinical data and peripheral blood samples of the family were collected. Potential variants were screened by using a panel for genes associated with intellectual impairment. Suspected variants were verified by PCR and Sanger sequencing. Results The child presented with mental retardation, language delay and poor self-care. Imaging analysis showed widening of brain fissures and subarachnoid space, and dysplasia of corpus callosum. Three novel heterozygous variants, namely c. 1705T>C(p.S569P), c. 1708dupC (p.R570Pfs*80) and c. 2273delA (p.N758Tfs*22), were identified in the TRAPPC9 gene. The mother of the proband has carried the c. 1708dupC (p.R570Pfs*80) and c. 1705T>C(p.S569P) variants, while his father has carried the c. 2273delA (p.N758Tfs*22) variant. Conclusion The compound heterozygous variants of the TRAPPC9 gene probably underlie the disease in this family. Considering the clinical and genetic heterogeneity of mental retardation, genetic testing is essential for attaining diagnosis for patients with the relevant phenotype. Key words: Mental retardation, autosomal recessive 13; TRAPPC9 gene; Double variant; Compound heterozygous variant