PKD1L1 encodes polycystin-1L1, a ciliary protein essential for left-right axis specification during embryonic development. The protein functions as a component of calcium-permeant ion channels in primary cilia, where it controls cilium calcium concentration and regulates sonic hedgehog signaling 1. PKD1L1 forms mechanosensitive and temperature-sensitive channel complexes with PKD2L1, facilitating flow detection in left-right patterning 1. The protein contains multiple domains including Ig-like PKD, REJ, GPS, and transmembrane domains, with G-protein-coupled receptor signatures 1. PKD1L1 is expressed in testis, heart, and specifically in Leydig cells 1. Loss-of-function mutations cause heterotaxy syndrome with congenital heart defects, visceral malformations, and situs abnormalities 234. Additional phenotypes include biliary atresia with bile duct dysmorphogenesis and ciliopathy when deleted in liver tissue 5, congenital chylothorax with fetal hydrops 6, and congenital asplenia 3. The gene represents part of a vertebrate-specific genetic module controlling left-right asymmetry 7. Clinical significance includes its role as a monogenic cause identified in 56% of laterality disorder cases through whole-exome sequencing 2.