Phenotypic Spectrum in a Family Sharing a Heterozygous Variant.

Background And Purpose: Mutations in have classically been associated with benign familial neonatal and infantile seizures and more recently identified in patients with neurodevelopmental disorders and abnormal electroencephalogram (EEG) findings. We present 4 affected patients from a family with a pathogenic mutation in with a unique constellation of clinical findings.

Methods: A family of 3 affected siblings and mother sharing a pathogenic variant are described, including clinical history, genetic results, and EEG and magnetic resonance imaging (MRI) findings.

Results: This family shows a variety of clinical manifestations, including neonatal seizures, developmental delays, autism spectrum disorder, and anxiety. One child developed absence epilepsy, 2 children have infrequent convulsive seizures that have persisted into childhood, and their parent developed adult-onset epilepsy. An underlying c.1091G>A (R364H) variant in was found in all affected individuals.

Conclusions: The phenotypic variability of KCNQ3 channelopathies continues to expand as more individuals and families are described, and the variant identified in this family adds to the understanding of the manifestations of -related disorders.