The roles of homocysteinemia and methylmalonic acidemia in kidney injury in atypical hemolytic uremic syndrome caused by cobalamin C deficiency

• Published in: Pediatric nephrology (Berlin, West) Vol. 37; no. 6; pp. 1415 - 1418
• Main Authors: Wood, William D., Elmaghrabi, Ayah, Gotway, Garrett, Wolf, Matthias T. F.
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01.06.2022; Springer; Springer Nature B.V
• Subjects: Aciduria; Acute Kidney Injury - etiology; Amino Acid Metabolism, Inborn Errors; Atypical Hemolytic Uremic Syndrome - complications; Atypical Hemolytic Uremic Syndrome - diagnosis; Atypical Hemolytic Uremic Syndrome - genetics; Brief Report; Carnitine; Case studies; Complications and side effects; Female; Genetic screening; Health aspects; Hemolytic uremic syndrome; Homocysteine; Humans; Hyperhomocysteinemia; Hyperhomocysteinemia - complications; Infant, Newborn; Kidney - pathology; Kidney diseases; Kidneys; Medicine; Medicine & Public Health; Metabolic disorders; Methionine; Methylmalonic Acid; Methylmalonic acidemia; Methylmalonyl-CoA; Nephrology; Oxidoreductases - genetics; Patients; Pediatrics; Protein turnover; Risk factors; Succinyl-CoA; Thrombocytopenia; Thrombotic Microangiopathies - pathology; Thrombotic microangiopathy; Urology; Vitamin B 12; Vitamin B 12 Deficiency - complications; Vitamin B 12 Deficiency - diagnosis; Vitamin B12; Vitamin B12 deficiency; United States; aHUS; Thrombotic microangiopathy; Cobalamin C; Acute kidney injury
• ISSN: 0931-041X; 1432-198X; 1432-198X
• DOI: 10.1007/s00467-021-05372-6

Background Cobalamin C (cblC), a vitamin B12 processing protein, plays a crucial role in metabolism for the conversion of homocysteine to methionine and methylmalonyl-CoA to succinyl-CoA. CblC deficiency, an inborn error of cobalamin processing, is a rare cause of atypical hemolytic-uremic syndrome (aHUS) and results in hyperhomocysteinemia and methylmalonic aciduria. Both substances are thought to contribute to thrombotic microangiopathy (TMA) in cblC deficiency patients. However, the roles of homocysteine and methylmalonic acid (MMA) in these patients remain unclear. We want to shed more light on the contributions of homocysteine and MMA levels as contributing factors for thrombotic microangiopathy (TMA)/aHUS by a follow-up of a cblC deficiency patient over 6 years. Case diagnosis A 27-day-old Hispanic female presented with abnormal C3-carnitine on her newborn screen, poor feeding, decreased activity, and oligouria. She was diagnosed with cblC deficiency after laboratory results revealed elevated serum homocysteine, and serum MMA along with genetic testing showing a homozygous pathogenic frameshift variant in MMACHC . The patient developed aHUS and acute kidney injury (AKI), which resolved after appropriate therapy. Over 6 years, she continued to have normal kidney function with no thrombocytopenia despite persistently elevated homocysteine and MMA levels. Conclusion We question the roles of homocysteine and MMA as causative of aHUS/TMA in cblC deficiency as they remained elevated during follow-up but did not result in aHUS/TMA or AKI. Hyperhomocysteinemia and/or MMA caused by other metabolic diseases do not result in aHUS/TMA or AKI. This suggests that other nephrotoxic factors may trigger aHUS/TMA in cblC patients.