Health condition
Congenital disorders of glycosylation
Congenital disorders of glycosylation (CDG) are a large family of inherited conditions affecting how the body attaches sugar chains to proteins - hugely variable, increasingly diagnosed by genomic testing at all ages.
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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Over 150 subtypes; PMM2-CDG is the most common - most are autosomal recessive
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Features span neurology (ataxia, seizures, developmental issues), liver dysfunction, clotting abnormalities, hormone problems and unusual fat distribution
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Screening uses transferrin isoform analysis; whole exome or genome sequencing identifies the subtype
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A few subtypes have specific treatments - for the rest, coordinated surveillance matters
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
Glycosylation - decorating proteins with sugar chains - touches almost every organ system, which is why CDG can look like nearly anything: an ataxic child who becomes an adult with stable coordination problems, unexplained abnormal liver enzymes with odd clotting results, or multi-system illness that has defied classification for years. Milder subtypes definitely reach adulthood undiagnosed, and CDG regularly emerges from whole genome sequencing in the diagnostic-odyssey population.
Testing, surveillance and specialist care
A transferrin glycoform screen is a useful biochemical pointer, but genomic sequencing has become the definitive route to a subtype, and the subtype dictates prognosis, surveillance and - for entities like MPI-CDG - specific treatment. Care is coordinated through metabolic centres, with genetic counselling for parents, siblings and family planning. 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 Congenital disorders of glycosylation.
Quick, plain-English answers to what people ask us most.
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What are congenital disorders of glycosylation?
Congenital disorders of glycosylation (CDG) are a group of rare inherited metabolic conditions affecting the body's ability to properly attach sugar molecules (glycosylation) to proteins and fats, a process essential for the normal function of many cells and organs throughout the body. Because glycosylation affects so many different proteins, these conditions can cause a wide range of symptoms affecting multiple body systems simultaneously. There are many specific subtypes, each caused by a different genetic defect within this complex process.
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What causes CDG?
These conditions are caused by inherited genetic mutations affecting one of the many enzymes involved in the complex, multi-step process of glycosylation. Most types are inherited in an autosomal recessive pattern, meaning both parents carry one copy of the altered gene. Genetic testing can identify the specific gene and mutation involved, which helps confirm the diagnosis and clarify the specific subtype.
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What symptoms do congenital disorders of glycosylation cause?
Symptoms vary enormously depending on the specific subtype and can include developmental delay, neurological symptoms, poor growth, liver problems, immune deficiency, and abnormalities affecting multiple other organs, reflecting the widespread role of glycosylation throughout the body. Severity ranges from relatively mild to very severe, life-limiting disease depending on the specific genetic defect. This wide variability makes early, specific diagnosis particularly important for guiding appropriate management and family counselling.
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How are CDG diagnosed?
Diagnosis often involves specific blood tests looking for abnormal glycosylation patterns on certain proteins, alongside genetic testing to identify the specific underlying gene mutation. Because of the wide range of possible symptoms, diagnosis can sometimes take time and specialist input, particularly in less clear-cut cases. A specialist metabolic medicine team with experience in these rare conditions typically leads this detailed diagnostic process.
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How are CDG managed?
Management is highly individualised based on the specific subtype and which organ systems are affected, and can include supportive treatments for specific symptoms (such as nutritional support, physiotherapy, or seizure management), and for a small number of specific subtypes, targeted treatments addressing the underlying metabolic defect directly. Given the rarity and complexity of these conditions, care is usually coordinated by a specialist metabolic medicine centre. Multidisciplinary support across various specialities is often needed given the wide-ranging effects on the body.
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When should I see a specialist?
If a child has unexplained developmental delay alongside features affecting multiple body systems, or a specific CDG diagnosis is suspected, referral to a specialist metabolic medicine centre is important for detailed assessment. NHS metabolic medicine referral can take several weeks to months given the specialised nature of these services; a private consultation can help arrange earlier initial assessment and appropriate specialist referral.