CFTR and Meconium ileus: Meconium ileus displays heritability estimates of ~88% [6] and can be discordant for CF siblings with identical CFTR mutations, further highlighting the importance of genetic background beyond CFTR. Meconium, or first stool of a newborn, is typically comprised of intestinal mucins, proteins, bile salts, and cellular debris that are shed from the intestinal mucosa during the fetal period [7].