Background: Okur-Chung neurodevelopmental syndrome is a rare autosomal dominant developmental disorder that is characterized by delayed psychomotor development, behavioral problems, and variable dysmorphic features. This syndrome is caused by heterozygous mutations in the CSNK2A1 gene. Since this is a novel and rare clinical entity, the phenotypic spectrum of the syndrome remains unclear.

Case report: A Japanese male patient was born at 41 weeks of gestation after an uncomplicated pregnancy and delivery. He had distinctive facial features consisting of a prominent forehead, arched eyebrows, hypertelorism, a broad nasal bridge, a thin upper lip, and opened mouth. He also presented with sensorineural hearing loss due to cochlear nerve canal dysplasia and a history of a cluster of neonatal seizures. Neurodevelopmental delay and short stature became evident. At the last examination at 3 years of age, he could speak only a few meaningful words and exhibited intellectual disability (DQ 67).

Genetic analysis: Trio-whole-exome sequencing identified a de novo heterozygous missense mutation (c.593A>G, p.Lys198Arg) in CSNK2A1, which has been previously reported in multiple patients with Okur-Chung neurodevelopmental syndrome.

Conclusion: Trio whole-exome sequencing is a powerful tool for diagnosis of rare syndromic disorders with variable phenotypes. This is the first report of possible association between CSNK2A1 mutation and phenotypes of hearing loss with cochlear nerve canal dysplasia and neonatal seizure.