[A case of late-onset cobalamin C disease (methylmalonic aciduria and homocystinuria, cobalamin C type)].

: We report the case of an 18-year-old Japanese woman with cobalamin (cbl) C disease. She was born between non- consanguineous parents, and had easy fatigability from a childhood. At 14 years old, she developed renal failure, and had repeated psychosis during 2 years. At 16 old, she developed her gait disturbance and her symptoms fluctuated, but the cause of gait disturbance was unclear. At 18 years old, she was admitted with worsening of gait disturbance. Physical examination revealed spastic paraparesis and bilateral peroneal nerve paralyses. Homocystinuria and methylmalonic aciduria were detected, although serum vitamin B12 was within normal range. Gene mutation analysis revealed Gly147Asp (440G>A) and Trp157Ser (470G>C) in the MMACHC gene as a compound heterozygous mutation. We diagnosed her as having late-onset cbl C disease, and her gait disturbance and renal failure improved after intramuscular hydroxocobalamin administration. Although late-onset cbl C disease is rare in Japan, it an important to consider this congenital disease because symptoms are expected to improve by medical intervention.