Beyond a routine blood gas, an easily picked but missed diagnosis of chronic Encephalopathy

Recessive congenital methemoglobinemia (RCM) is a rare neurological disorder caused by a deficiency in NADH-CYB5R. RCM has two main types I&II, with cyanosis being the hallmark feature in both. Type-I is a mild form, with cyanosis being the only feature. While type-II is the severe form with prominent neurological symptoms including, dystonia and spasticity. However, the cyanosis is subtle and difficult to appreciate. The cyanosis in RCM is treated with ascorbic-acid or methylene-blue. However, those treatments will not alter the neurological complication. In this paper, we report two cases of RCM type-II in Saudi siblings. They presented with cyanosis at birth; a CO-oximetry was done showing a high level of methemoglobin and a trail of methylene blue was used. The siblings were followed up and showed signs of developmental delay, hypotonia, exaggerated reflex, and seizure. A genetic analysis was requested, which showed missense mutation (c.274 C > T), leading to amino acid substitution; p. Arg92Trp.