2- 3% of population are affected by neurodevelopmental disorders (NDDs), causing severe intellectual impairment, health complications and reduced life expectancy. In approximately half of the affected individuals the causal genetic variants remain unknown. Utilizing a comprehensive genetic screening strategy in a cohort of consanguineous families with multiple affected children, several gene variants associated with NDDs were identified. Among these, KCNH5 emerged as a compelling candidate due to its high expression in the nervous system and high degree of conservation in Drosophila melanogaster. Our study aims to elucidate the function of the fly orthologue, eag, and assess the ability of KCNH5 and the patient-derived variant to rescue its function in vivo. We conducted electrophysiological characterization of KCNH5 and its patient-derived variant using whole-cell- and single-channel-recordings to reveal potential functional changes. We additionally established assays for testing functional defects in eag-deficient Drosophila larvae in locomotion and nociceptive behavior. Furthermore, we characterized morphological differences of Drosophila sensory neurons in eag-deficient larvae. We aim to rescue the characterized functional and morphological defects of eag-mutant flies by expressing human KCNH5 and its patient variant, thereby assessing the pathogenic potential of the variant. We aim to further unravel the electrophysiological and functional properties of KCNH5 using the fly model, which should establish a system to assess pathogenicity of patient variants and further our understanding of NDDs.