Biochemical Analysis of a Patient with Fumarate Hydratase Deficiency

Abstract

Mutations in the human FH gene are associated with the rare recessive metabolic disease known as Fumarate Hydratase Deficiency (FHD). Symptoms associated with FHD include brain malformations, developmental delays, poor growth, and seizures. Many FHD patients do not survive past early childhood. The FH gene encodes the Krebs cycle enzyme fumarate hydratase, also known as fumarase. We describe the symptoms and treatment of a female adolescent with FHD, along with a biochemical analysis of the patient's fumarase variants. While FHD patients commonly experience infantile spasms, the patient had epileptic spasms that occurred only later in childhood. After several first line medication trials failed, the patient responded well to lacosamide for her seizures. We biochemically analyzed the patient's two fumarase variants, introducing each of the mutations (D65G and E432Kfs*17) into a recombinant plasmid containing the human FH gene. We purified and characterized wild-type fumarase along with the variants. E432Kfs*17 had defects in oligomerization and catalysis, including a ~1500-fold decrease in turnover (kcat). The variant D65G displayed oligomerization and turnover similar to wild-type, and only a very mild defect in Km. We hypothesize that the rather mild deficiency of the D65G variant may have contributed to the mild clinical severity of the patient.