A case report of autosomal recessive methemoglobinemia in a child

Aline Khalil1, Duaa AL Lawati2,3, Patcha Yenjabog3,4, Ziad Kazzi1,3 , Tharwat EL Zahran1

1Department of Emergency Medicine, American University of Beirut Medical Center, Beirut, Lebanon
2Department of Emergency Medicine, Khoula Hospital, Ministry of Health, Muscat, Oman
3Department of Emergency Medicine, Emory University, Atlanta, Georgia, USA
4Department of Pediatrics, Division of Pediatric Pulmonary and Critical Care, Faculty of Medicine, Vajira Hospital, Navamindradhiraj University, Bangkok, Thailand

Keywords: Case reports, cyanosis, genetic testing, methemoglobinemia, pediatrics

Abstract

Methemoglobinemia is a rare hematologic disorder characterized by impaired oxygen delivery due to oxidation of hemoglobin iron from the ferrous (Fe2+) to the ferric (Fe3+) state, leading to elevated methemoglobin (MetHb) levels and cyanosis. We report the case of a 3 year old female with a history of congenital cyanotic heart disease who presented with worsening cyanosis and was found to have a MetHb level of 49.3%. She responded initially to methylene blue therapy, but levels fluctuated over the following week. Whole exome sequencing revealed a homozygous missense variant in the cytochrome b5 (CytB5) reductase 3 gene, consistent with autosomal recessive methemoglobinemia due to CytB5 reductase deficiency. The identified variant has not been previously reported and was classified as a variant of uncertain significance. This case underscores the importance of considering hereditary methemoglobinemia in children with unexplained cyanosis and persistent MetHb elevation. Genetic evaluation remains essential in suspected hereditary cases to inform prognosis, guide long term care, and support family counseling.

How to cite this article: Khalil AK, AL Lawati D, Yenjabog P, Kazzi Z, EL Zahran T. A case report of autosomal recessive methemoglobinemia in a child. Turk J Emerg Med 2026;26:351-4.