Hyperkinetic stereotyped movements in a boy with biallelic CNTNAP2 variants.

This case expands the molecular and phenotypic spectrum of CASPR2 deficiency disorder, suggesting that Hyperkinetic stereotyped movements may be a rare, yet significant, clinical feature of this complex neurological disorder. Furthermore, the identification of an in-frame, largely non-coding duplication in CNTNAP2 points to a sophisticated underlying molecular mechanism, likely involving impaired FOXP2 binding.