Congenital cyanosis due to methemoglobin reductase deficiency: first reported Tunisian case

During investigation of chronic cyanosis in a 25 year old male, after excluding pulmonary and cardiac causes, methemoglobinemia was suspected. Investigation of the activity of methemoglobin reductase clenched the diagnosis of homozygous cytochrome b5 reductase deficiency in a case of recessive congenital methemoglobin type I (absence of neurologic symptoms).