Deletion of Mfrn1 in hepatocytes leads to increased protoporphyrin IX in mice fed ALA. ALA was added to the drinking water of mice of the noted genotypes. Four weeks later, the ALA-fed mice and control mice were killed and the level of protoporphyrin IX (PPIX) measured in plasma (A), liver (B), and erythrocytes (C). (D) PCR analysis of Mfrn1 deletion in fibroblasts incubated with Tat-Cre. (E) Levels of PPIX in wild-type and Mfrn1-deleted fibroblasts. *P < .05.