We report an inborn error of the tricarboxylic acid cycle, fumarase deficiency, in two siblings born to first cousin parents. They presented with progressive encephalopathy, dystonia, leucopenia, and neutropenia. Elevation of lactate in the cerebrospinal fluid and high fumarate excretion in the
Fumarase deficiency is a rare autosomal recessive inborn error of metabolism of the Krebs Tricarboxylic Acid cycle. A heavy neurological disease burden is imparted by fumarase deficiency, commonly manifesting as microcephaly, dystonia, global developmental delay, seizures, and lethality in the