Genetic and cellular studies of oxidative stress in methylmalonic aciduria (MMA) cobalamin deficiency type C (cblC) with homocystinuria (MMACHC).

[homocystinuria without methylmalonic aciduria]

Methylmalonic aciduria (MMA ) cobalamin deficiency type C (cblC ) with homocystinuria (MMACHC ) is the most frequent genetic disorder of vitamin B (12 ) metabolism . The aim of this work was to identify the mutational spectrum in a cohort of cblC-affected patients and the analysis of the cellular oxidative stress and apoptosis processes , in the presence or absence of vitamin B (12 ). The mutational spectrum includes nine previously described mutations : c .3 G >A (p .M 1 L ), c .217 C >T (p .R 73 X ), c .271 dupA (p .R 91 KfsX 14 ), c .331 C >T (p .R 111 X ), c .394 C >T (p .R 132 X ), c .457 C >T (p .R 153 X ), c .481 C >T (p .R 161 X ), c .565 C >A (p .R 189 S ), and c .615 C >G (p .Y 205 X ), and two novel changes , c .90 G >A (p .W 30 X ) and c .81 +2 T >G (IVS 1 +2 T >G ). The most frequent change was the known c .271 dupA mutation , which accounts for 85 % of the mutant alleles characterized in this cohort of patients . Owing to its high frequency , a real-time PCR and subsequent high -resolution melting (HRM ) analysis for this mutation has been established for diagnostic purposes . All cell lines studied presented a significant increase of intracellular reactive oxygen species (ROS ) content , and also a high rate of apoptosis , suggesting that elevated ROS levels might induce apoptosis in cblC patients . In addition , ROS levels decreased in hydroxocobalamin-incubated cells , indicating that cobalamin might either directly or indirectly act as a scavenger of ROS . ROS production might be considered as a phenotypic modifier in cblC patients , and cobalamin supplementation or additional antioxidant drugs might suppress apoptosis and prevent cellular damage in these patients .