Exocrine pancreatic insufficiency, dyserythropoeitic anemia, and calvarial hyperostosis are caused by a mutation in the COX4I2 gene.

Steatorrhea and malabsorption of lipid-soluble vitamins due to exocrine pancreatic insufficiency are common in patients with cystic fibrosis and are predominant in Shwachman-Bodian-Diamond, Pearson, and Johanson-Blizzard syndromes. In four patients who suffered from congenital exocrine pancreatic insufficiency, dyserythropoeitic anemia, and calvarial hyperostosis, we excluded these disorders and identified, by using homozygosity mapping, a mutation in the COX4I2 gene. The COX4 protein is an essential structural subunit of cytochrome c oxidase complex and has two isoforms, encoded by two different genes.