In our idiopathic speech delay cohort, we identified a pathogenic frameshift variant in SETD1A and likely pathogenic variants in SPTBN1 and ARF3. In the remaining 20 probands, multiple rare pLoF and likely deleterious missense variants were identified that might play causal roles in the observed speech delay, but that require additional evidence to be formally classified as pathogenic. Here, SETD1A is linked to Delayed speech and language development.