A Novel Missense Variant in the NKX2-1 Prevents Transcriptional Rescue by TAZ.

Brain-lung-thyroid syndrome (BLTS) is caused by haploinsufficiency, resulting in chorea/choreoathetosis, respiratory problems, and hypothyroidism. Genes interacting with NKX2-1 mutants influence its phenotypic variability. We report a novel missense variant and the modifier function of TAZ/WWTR1 in BLTS. A child with BLTS underwent next-generation sequencing panel testing for thyroid disorders. His family was genotyped for variants and screened for germline mosaicism. Mutant was generated, and transactivation assays were performed on three NKX2-1 target gene promoters. DNA binding capacity and protein-protein interaction were analyzed. The patient had severe BLTS and carried a novel missense variant c.632A>G (p.N211S) in , which failed to bind to specific DNA promoters, reducing their transactivation. cotransfection did not significantly increase transcription of these genes, although the variant retained its ability to bind to TAZ. We identify a novel pathogenic variant that causes severe BLTS and is inherited through germline mosaicism. The mutant lacks DNA-binding capacity, impairing transactivation and suggesting that NKX2-1 binding to DNA is essential for TAZ-mediated transcriptional rescue.