Case report of paroxysmal dystonia in a child with KBG syndrome: Expansion of the phenotype and utility of whole exome sequencing.

RATIONALE

KBG syndrome is a rare, autosomal dominant neurodevelopmental disorder characterized by developmental delay, macrodontia, distinctive facial features, and a range of systemic manifestations.

PATIENT CONCERNS

We report a pediatric patient with a history of global developmental delay, autism spectrum disorder, sensorineural hearing loss, and spastic diplegia who developed episodic, unilateral dystonic spells beginning at age 7, leading to impaired mobility.

DIAGNOSES

Initial genetic testing revealed a maternally inherited 3p26 duplication, which did not fully account for the patient's clinical presentation. Whole exome sequencing (WES) was subsequently performed and identified a pathogenic frameshift mutation in ANKRD11, confirming a diagnosis of KBG syndrome. Additional genetic variants were found in CDH23, potentially explaining the patient's profound hearing loss.

INTERVENTIONS

After receiving a diagnosis, the patient received multidisciplinary care including intensive speech, occupational, physical, applied behavior analysis therapies, and educational planning to address his neurodevelopmental needs.

OUTCOMES

WES established a unifying diagnosis that better accounted for the patient's constellation of findings. Recognition of KBG syndrome facilitated appropriate medical, rehabilitative, and educational interventions. The presence of paroxysmal dystonia, previously unrecognized in KBG syndrome, adds to the expanding phenotypic spectrum.

LESSONS

This case underscores the diagnostic value of WES in patients with complex neurodevelopmental presentations and unexplained movement disorders. Our findings support the inclusion of ANKRD11 in the differential for pediatric dystonia and suggest a potential, previously underrecognized neurologic feature of KBG syndrome. Broader access to genomic diagnostics may reduce the diagnostic odyssey for similar patients and inform more targeted care strategies.