MAP3K15 (mitogen-activated protein kinase kinase kinase 15) is a serine/threonine kinase that functions as an upstream component of the MAP kinase signaling pathway, particularly activating the p38 MAPK cascade through phosphorylation of downstream MAP kinase kinases 1. The protein plays a protective role against metabolic dysfunction, as rare damaging variants in MAP3K15 are associated with 30% reduced risk of diabetes development and lower glycosylated hemoglobin levels, independent of body mass index 2. This protective effect extends to both type 1 and type 2 diabetes, with protein-truncating variants showing similar benefits in Finnish populations 2. MAP3K15 variants have been implicated in male-predominant congenital heart disease, where X-linked rare damaging variants contribute to sex differences in disease prevalence 3. The gene has also been identified as a potential biomarker in various conditions including nonobstructive azoospermia 4, giant congenital melanocytic nevus 5, and idiopathic pulmonary fibrosis 6. Additionally, MAP3K15 serves as a specific marker for hippocampal CA2 neurons, enabling targeted research of this brain region's role in social memory 7. The gene's diverse roles suggest it functions as an important regulatory node in multiple physiological pathways.