Orotic aciduria 1

A disorder of pyrimidine metabolism resulting in megaloblastic anemia and orotic acid crystalluria that is frequently associated with some degree of physical and intellectual disability. A minority of cases have additional features, particularly congenital malformations and immune deficiencies.

Mitochondrial DNA depletion syndrome 8A

A disorder due to mitochondrial dysfunction characterized by various combinations of neonatal hypotonia, neurological deterioration, respiratory distress, lactic acidosis, and renal tubulopathy.

Mitochondrial DNA depletion syndrome 2

A disorder due to mitochondrial dysfunction characterized by childhood onset of muscle weakness associated with depletion of mtDNA in skeletal muscle. There is wide clinical variability; some patients have onset in infancy and show a rapidly progressive course with early death due to respiratory failure, whereas others have later onset of a slowly progressive myopathy.

P5N deficiency

Autosomal recessive condition causing hemolytic anemia characterized by marked basophilic stippling and the accumulation of high concentrations of pyrimidine nucleotides within the erythrocyte. It is implicated in the anemia of lead poisoning and is possibly associated with learning difficulties.

Beta-ureidopropionase deficiency

An inborn error of metabolism due to a defect in pyrimidine degradation. It is characterized by muscular hypotonia, dystonic movements, scoliosis, microcephaly and severe developmental delay. Patients show strongly elevated levels of N-carbamyl-beta-alanine and N-carbamyl-beta-aminoisobutyric acid in plasma, cerebrospinal fluid and urine.

Dihydropyrimidinase deficiency

An autosomal recessive disorder of pyrimidine metabolism characterized by dihydropyrimidinuria. It is associated with a variable clinical phenotype characterized by epileptic or convulsive attacks, dysmorphic features and severe developmental delay, and congenital microvillous atrophy. Most patients are, however, asymptomatic.

Dihydropyrimidine dehydrogenase deficiency

A metabolic disorder with large phenotypic variability, ranging from no symptoms to a convulsive disorder with motor and intellectual disability. It is characterized by persistent urinary excretion of excessive amounts of uracil, thymine and 5-hydroxymethyluracil. Patients suffering from this disease show a severe reaction to the anticancer drug 5-fluorouracil.

Mitochondrial DNA depletion syndrome 20, MNGIE type

An autosomal recessive mitochondrial disorder characterized by severe gut dysmotility, muscle weakness and atrophy, neurological abnormalities including epilepsy, migraine, stroke-like episodes, learning difficulties or cognitive decline, and neurogenic bladder. Brain imaging usually shows diffuse leukoencephalopathy and may show cerebellar atrophy. Disease onset can range from infancy to the teenage years.

Progressive external ophthalmoplegia with mitochondrial DNA deletions, autosomal dominant, 1

A disorder characterized by progressive weakness of ocular muscles and levator muscle of the upper eyelid. In a minority of cases, it is associated with skeletal myopathy, which predominantly involves axial or proximal muscles and which causes abnormal fatigability and even permanent muscle weakness. Ragged-red fibers and atrophy are found on muscle biopsy. A large proportion of chronic ophthalmoplegias are associated with other symptoms, leading to a multisystemic pattern of this disease. Additional symptoms are variable, and may include cataracts, hearing loss, sensory axonal neuropathy, ataxia, depression, hypogonadism, and parkinsonism.

Mitochondrial DNA depletion syndrome 1, MNGIE type

A multisystem disease associated with mitochondrial dysfunction. It is clinically characterized by onset between the second and fifth decades of life, ptosis, progressive external ophthalmoplegia, gastrointestinal dysmotility (often pseudoobstruction), diffuse leukoencephalopathy, cachexia, peripheral neuropathy, and myopathy.