Other names: MoCD Type A

Molybdenum cofactor deficiency (MoCD) type A is an ultra-rare, autosomal recessive, inborn error of metabolism caused by disruption in molybdenum cofactor (MoCo) synthesis.

MoCD type A is caused by mutations in the molybdenum cofactor synthesis 1 gene (MOCS1). The deficiency in molybdenum cofactor (MoCo) production leads to the lack of molybdenum-dependent enzyme activity resulting in decreased sulfite oxidase activity and buildup of sulfite and secondary metabolites (such as S-sulfocysteine (SSC)) in the brain. This causes irreversible neurological damage.

MoCD Type A presents shortly after birth, often with severe encephalopathy and intractable seizures. Neurological damage leads to severe psychomotor impairment and an inability to make coordinated movements.

Nulibry (fosdenopterin) is the first approved therapy to reduce the risk of mortality in patients with MoCD Type A. It works as a substrate replacement therapy that provides an exogenous source of cyclic pyranopterin monophosphate (cPMP), which is converted to molybdopterin. Molybdopterin is then converted to molybdenum cofactor, which is needed for the activation of molybdenum-dependent enzymes, including sulfite oxidase.

Drugs used to treat Molybdenum Cofactor Deficiency Type A