Primary deficiency of Coenzyme Q10 (CoQ10, CoQ, ubiquinone) encompasses a heterogeneous group of disorders caused by molecular defects in genes encoding proteins required for biosynthesis of CoQ10, an essential lipid that is endogenously synthetized and exerts crucial functions within cells. Patients with CoQ10 deficiency have reduced levels of CoQ in tissues. COQ2 encodes for the enzyme required for the second step of the final reaction sequence of CoQ10 biosynthesis. Mutations in COQ2 were first described in 2006 and cause a defect in CoQ10 biosynthesis.

Clinical features
Mutations in COQ2 can affect different organs and the clinical picture is extremely variable with different age of onset, ranging from a severe neonatal multisystemic disorder to nephrotic syndrome with or without encephalopathy, to an adult-onset multisystem atrophy-like atrophy phenotype.

The estimated incidence of all primary coenzyme Q10 deficiencies is less than 1:100,000. The exact prevalence of this condition is currently unknown, because of the lack of precise epidemiologic data. However, COQ2-associated CoQ10 deficiency is an ultra-rare disease and so far, approximately 20 families harbouring defects in this gene have been reported. Since this condition has been described in 2006, it is possible that its frequency is under-estimated.

The disease is inherited as an autosomal recessive condition: biallelic mutations (in homozygosity or compound heterozygosity) are required to manifest the disease. Patients parents are asymptomatic carriers and at conception each sibling of a patient has a 25% risk of being affected.