TCF15 (transcription factor 15) is a basic helix-loop-helix (bHLH) transcription factor that plays crucial roles in early embryonic development and tissue-specific gene regulation 1. The gene consists of two exons separated by a 5-kb intron and is located on chromosome 20 1. TCF15 functions by forming heterodimers with other bHLH proteins, such as MEOX2, to regulate transcription of target genes through E-box DNA binding motifs 2. In cardiovascular biology, MEOX2/TCF15 heterodimers are highly expressed in heart capillary endothelial cells where they regulate fatty acid transport by controlling expression of CD36 and lipoprotein lipase, facilitating fatty acid uptake and transfer to cardiomyocytes 2. Combined haplodeficiency of both genes impairs cardiac contractility, highlighting their clinical significance 2. During embryonic development, TCF15 is essential for paraxial mesoderm formation and axis extension, with cis-regulatory elements controlling its spatiotemporal expression during somitogenesis 3. Genetic variation in MEOX2, but interestingly not TCF15, has been associated with coronary heart disease risk in population studies 4. TCF15 expression is also dysregulated in various pathological conditions including preterm birth 5 and colorectal cancer, where it functions as part of epithelial-mesenchymal transition regulatory networks 6.