Defects in SLC6A1 can cause epilepsy and developmental delay (MIM 616421), overlapping with the presentation observed and reported to date in patients with deleterious variants in TCF20. For all the other patients, the clinical test referenced in this study, either exome sequencing or microarray, did not detect additional pathogenic or likely pathogenic variants in other known disease genes underlying the observed neurodevelopmental disorder. The gene discussed is TCF20; the disease is neurodevelopmental disorder.