Case presentation: a severe case of cobalamin c deficiency presenting with nephrotic syndrome, malignant hypertension and hemolytic anemia.

Background: The etiology of nephrotic syndrome can vary, with underlying metabolic diseases being a potential factor. Cobalamin C (cblC) defect is an autosomal recessive inborn error of metabolism caused by mutations in the MMACHC gene, resulting in impaired vitamin B12 processing. While cblC defect typically manifests with hematological and neurological symptoms, renal involvement is increasingly recognized but remains rare.

Case Presentation: We describe a 7-month-old male patient presenting with fatigue and edema. His first laboratory findings showed anemia, thrombocytopenia, hypoalbuminemia and proteinuria and further examinations reveals hemolysis in peripheric blood smear. During his follow up respiratory distress due to pleural effusion in the right hemithorax was noticed. And fluid leakage to the third spaces supported nephrotic syndrome diagnosis. The patient's condition deteriorated, leading to intensive care admission due to, hypertensive crisis, and respiratory distress. High total plasma homocysteine and low methionine levels raised suspicion of cobalamin metabolism disorders. Genetic testing confirmed biallelic MMACHC gene mutations, establishing the diagnosis of cblC defect. Treatment with hydroxycobalamin, folic acid, and betaine led to remarkable clinical improvement.

Discussion/conclusion: This case underscores the significance of recognizing metabolic disorders like cblC defect in atypical presentations of nephrotic syndrome. Early diagnosis and comprehensive management are vital to prevent irreversible renal damage. While cblC defects are more commonly associated with atypical hemolytic uremic syndrome, this case highlights the importance of considering cobalamin defects in the differential diagnosis of nephrotic syndrome, especially when associated with accompanying findings such as hemolysis. Our case, which has one of the highest homocysteine levels reported in the literature, emphasizes this situation again.