Asano et al. (1988) reported 2 female sibs with succinic acidemia, a hitherto unreported organic acidemia. Succinic acidemia, lactic acidosis, and respiratory distress were present in 1 sib, who died 37 days after birth. The second sib was ... Asano et al. (1988) reported 2 female sibs with succinic acidemia, a hitherto unreported organic acidemia. Succinic acidemia, lactic acidosis, and respiratory distress were present in 1 sib, who died 37 days after birth. The second sib was the product of a pregnancy that was electively terminated at 22 weeks. Serum succinic acid levels were greatly increased in both sibs and NADH-cytochrome c reductase activity was significantly low in both. In the fetal case, NADH-ferricyanide reductase activity was also low, suggesting a complex I deficiency of the electron transport system in the mitochondrial membrane. This was presumably an autosomal recessive disorder. Elpeleg and Hurvitz (1990) concluded that the sibs reported by Asano et al. (1988) had a form of mitochondrial complex I deficiency (252010). Elpeleg and Hurvitz (1990) noted that increased urinary levels of succinic acid is not unusual in sick infants and can be considered an accompanying nonspecific finding, not a new form of organic acidemia. They also reviewed the laboratory data reported by Asano et al. (1988), which were interpreted as consistent with isolated complex I deficiency.