KCNQ2 p.(Arg214Trp): systematic review with retrospective analysis and expanding the phenotype
Heterozygous pathogenic variants in the KCNQ2 gene underlie a broad phenotypic spectrum ranging from self-limited (familial) neonatal epilepsy (SeLNE) to developmental and epileptic encephalopathy or isolated intellectual disability. The KCNQ2 gene encodes subunits of a voltage-gated potassium channel involved in neuronal excitability, and its mutations are known to have both loss-of-function (LoF) and gain-of-function (GoF) effects, resulting in distinct neurological syndromes. The recurrent missense LoF variant KCNQ2 p.(Arg214Trp) has been previously reported in a single family with a presumed SeLNE phenotype, without detailed adult follow-up and with additional database-reported evidence suggesting a broader phenotype associated with this recurrent variant. Here, we report a family with two adult carriers of the heterozygous KCNQ2 p.(Arg214Trp) variant identified through whole-exome sequencing, including long-term follow-up into late adulthood. In addition, a literature review of previously reported cases carrying the same recurrent variant was performed. Both individuals presented with early-onset focal epilepsy with a relapsing course, characterized by prolonged seizure-free periods followed by recurrence in adulthood. The proband demonstrated transient motor regression, developmental delay, moderate intellectual disability, ataxia and fine motor impairment. The father exhibited milder cognitive impairment and additional comorbidities in later life. These findings challenge the concept of KCNQ2 p.(Arg214Trp) as a self-limited epilepsy-associated variant and indicate a broader phenotypic spectrum, with persistence of epilepsy and associated neurological and non-neurological comorbidities into adulthood. Our report provides new insights into adult outcomes, aiding in genetic counseling and the long-term management of affected individuals. More extensive studies with larger cohorts carrying this variant are necessary to better define the full phenotypic spectrum and to distinguish comorbidities associated with different etiological factors, including perinatal factors.