Sideroblastic anemia with B-cell immunodeficiency, periodic fevers, and developmental delay (SIFD) is a novel congenital sideroblastic anemia and immunodeficiency syndrome with additional features resembling a mitochondrial cytopathy. SIFD is caused by biallelic mutations in TRNT1, the gene encoding the CCA-adding enzyme essential for maturation of both nuclear and mitochondrial transfer RNAs.