A study of modifier genes for intestinal CF in human chromosome 19q13 has linked meconium ileus with polymorphic markers within the KCNN4 gene24 making its product, the KCa3.1, a strong candidate to modulate the severity of the effect of CFTR inactivation in intestinal function. The gene discussed is KCNN4; the disease is intestinal obstruction in the newborn due to guanylate cyclase 2C deficiency.