CNKSR2 gene mutation leads to Houge type of X-linked syndromic mental retardation: A case report and review of literature

RATIONALE: Mutations of connector enhancer of kinase suppressor of Ras-2 (CNKSR2) gene were identified as the cause of Houge type of X-linked syndromic mental retardation. The mutations of CNKSR2 gene are rare, we reporta patient carrying a novel nonsense mutation of CNKSR2,c.625C > T(p.Gln209(∗)) and review the clinical features and mutations of CNKSR2 gene for this rare condition considering previous literature. PATIENT CONCERNS: We report a case of a 7-year and 5-month-old Chinese patient with clinical symptoms of intellectual disability, language defect, epilepsy and hyperactivity. Genetic study revealed a novel nonsense variant of CNKSR2, which has not been reported yet. DIAGNOSIS: According to clinical manifestations, genetic pattern and ACMG classification of mutation site as Class 1-cause disease, the patient was diagnosed as Houge type of X-linked syndromic mental retardation caused by CNKSR2 gene mutation. INTERVENTIONS: The patient was administrated with a gradual titration of valproic acid (VPA). OUTCOMES: On administration of valproic acid, he had no further seizures. LESSONS: This is the first time to report a nonsense variant in CNKSR2, c.625C > T(p.Gln209(∗)), this finding could expand the spectrum of CNKSR2 mutations and might also support the further study of Houge type of X-linked syndromic mental retardation.