Purpose: The “NALCN channelosome” is an ion channel complex that consists of multiple proteins, including NALCN, UNC79, UNC80, and FAM155A. Only a small number of individuals with a neurodevelopmental syndrome have been reported with disease causing variants in NALCN and UNC80. However, no pathogenic UNC79 variants have been reported, and in vivo function of UNC79 in humans is largely unknown. Methods: We used international gene-matching efforts to identify patients harboring ultrarare heterozygous loss-of-function UNC79 variants and no other putative responsible genes. We used genetic manipulations in Drosophila and mice to test potential causal relationships between UNC79 variants and the pathology. Results: We found 6 unrelated and affected patients with UNC79 variants. Five patients presented with overlapping neurodevelopmental features, including mild to moderate intellectual disability and a mild developmental delay, whereas a single patient reportedly had normal cognitive and motor development but was diagnosed with epilepsy and autistic features. All displayed behavioral issues and 4 patients had epilepsy. Drosophila with UNC79 knocked down displayed induced seizure-like phenotype. Mice with a heterozygous loss-of-function variant have a developmental delay in body weight compared with wild type. In addition, they have impaired ability in learning and memory. Conclusion: Our results demonstrate that heterozygous loss-of-function UNC79 variants are associated with neurologic pathologies.