Health condition
Molybdenum cofactor deficiency
Molybdenum cofactor deficiency and isolated sulphite oxidase deficiency are rare recessive disorders in which sulphite accumulates and injures the brain - classically neonatal, with milder late-onset variants now recognised, and a targeted treatment (fosdenopterin) for type A disease.
Why trust this guide
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Editorial team
Written by our editorial team from the UK sources listed on each page.
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Sourced from guidance
Checked against current NHS and UK specialist society guidance at the time of review.
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Current for 2026
Reviewed on 2026-09-27 with the next review scheduled for 2027-09-27.
Key facts
The essentials at a glance.
Which gene and test confirm it, who should be tested in the family, and which specialist to see.
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Caused by variants in MOCS1, MOCS2, MOCS3 or GPHN (cofactor synthesis) or SUOX (isolated sulphite oxidase deficiency); all autosomal recessive
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Classic presentation: severe neonatal seizures and encephalopathy with very low plasma uric acid (in cofactor deficiency) and raised urinary sulphite
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Milder, later-onset forms exist - presenting with movement disorders, developmental regression or lens dislocation - and are underdiagnosed
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Fosdenopterin (cPMP replacement) treats MOCS1-related (type A) disease, making early molecular diagnosis genuinely urgent in infants
Understanding the condition
What it is and what happens next.
What causes it, how it is confirmed, and the testing and specialist routes available in the UK.
What it is and how it presents
The molybdenum cofactor powers a small set of enzymes, of which sulphite oxidase matters most: without it, sulphite - generated continuously from sulphur amino acid turnover - accumulates as a neurotoxin. The full deficiency devastates newborns within days, but partial enzyme function stretches the phenotype into childhood and beyond: an unexplained dystonia, seizures with lens dislocation mimicking homocystinuria, or stroke-like episodes in the basal ganglia on MRI. A near-absent plasma uric acid is the elegant, routinely available clue in cofactor deficiency - one of medicine's cheapest screening tests for one of its rarest diseases.
Testing, surveillance and specialist care
Confirmation runs through urinary sulphite and sulphocysteine, uric acid, and sequencing of the responsible genes, which now carries treatment weight given fosdenopterin's arrival for type A disease and dietary strategies trialled in milder SUOX deficiency. Affected families receive counselling on the 25% recurrence risk with prenatal and pre-implantation options through genetics services. NHS clinical genetics services carry some of the longest waits in the health service, often many months for a first appointment, whereas private genetic testing and a specialist review can typically be arranged within around two weeks.
Seeing a specialist
Who to see, and how quickly you can be seen.
The specialist for this condition is usually a metabolic physician (inherited metabolic disease clinic). Your GP can refer you on the NHS, or you can arrange a private consultation directly.
A quiet reminder
This guide is for information, not medical advice.
Your GP knows your history and can tell you which parts apply to you. If in doubt, see them - and seek urgent care for any emergency symptoms.
Frequently asked
Common questions about Molybdenum cofactor deficiency.
Quick, plain-English answers to what people ask us most.
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What is molybdenum cofactor deficiency?
Molybdenum cofactor deficiency is a rare, severe inherited metabolic disorder in which the body cannot make a cofactor needed by several essential enzymes, leading to toxic build-up of certain substances and severe neurological damage, usually presenting shortly after birth.
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What causes molybdenum cofactor deficiency?
It's caused by mutations in one of several genes needed to synthesise molybdenum cofactor, inherited in an autosomal recessive pattern, meaning both parents carry one copy of a faulty gene without necessarily being affected themselves.
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What are the symptoms of molybdenum cofactor deficiency?
Affected infants typically develop severe seizures shortly after birth, feeding difficulties, and rapid, significant developmental regression, reflecting the toxic effects of accumulated substances on the developing brain.
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Is molybdenum cofactor deficiency dangerous?
Yes, this is a very serious condition; most classic forms cause profound and irreversible brain damage, and historically the prognosis has been poor, though a specific treatable variant has recently been identified for one genetic type.
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Is molybdenum cofactor deficiency hereditary?
Yes, it's inherited in an autosomal recessive pattern, so parents of an affected child are both carriers, and future pregnancies carry a recurrence risk that genetic counselling can help families understand.
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Can molybdenum cofactor deficiency be treated?
For one specific genetic subtype, a substrate replacement therapy is now available and can be life-changing if started very early, but for other subtypes, treatment remains supportive, focused on seizure control and symptom management.
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When should families seek urgent specialist assessment for suspected molybdenum cofactor deficiency?
Any newborn with severe, treatment-resistant seizures shortly after birth needs urgent specialist metabolic and neurology assessment in hospital, since a treatable subtype exists and early diagnosis significantly affects outcome; this is an emergency assessment, not something to delay for a routine appointment.