Kidney-Limited Microangiopathy Associated with Methionine Synthase (Cobalamin G) Deficiency in a Pediatric Patient: Case Report and Review of the Literature.

Thrombotic microangiopathy (TMA) is a recognized sequela of inborn errors of metabolism impacting vitamin B12 (cobalamin) synthesis. Methylmalonic aciduria and homocystinuria, cobalamin deficiency type C is a well-known etiology for TMA. TMA has only rarely previously been reported in methionine synthase (cobalamin G) deficiency. Furthermore, results of only 7 kidney biopsies have previously been reported in this clinical setting. Here, we report a case of kidney- and glomerular-limited chronic active microangiopathy demonstrated on kidney biopsy in a patient with biochemically confirmed cobalamin G deficiency. A literature review of all prior reported cases is also presented and demonstrates hypertension, proteinuria, and hematuria to be common presenting symptoms. Age on onset ranged from 7 months to 14 years. Kidney-limited phenotype was less common and occurred only in older children. Acute kidney injury was more common in younger patients. Therapy with hydroxocobalamin and angiotensin-converting enzyme inhibitors resulted in variable clinical responses.