ALG1-congenital disorder of glycosylation

What it is, symptoms and effects

From: MedlinePlus Genetics, National Library of Medicine

ALG1-congenital disorder of glycosylation (ALG1-CDG, also known as congenital disorder of glycosylation type Ik) is an inherited disorder with varying signs and symptoms that typically develop during infancy and can affect several body systems.

Individuals with ALG1-CDG often have intellectual disability, delayed development, and weak muscle tone (hypotonia). Many affected individuals develop seizures that can be difficult to treat. Individuals with ALG1-CDG may also have movement problems such as involuntary rhythmic shaking (tremor) or difficulties with movement and balance (ataxia).

People with ALG1-CDG often have problems with blood clotting, which can lead to abnormal clotting or bleeding episodes. Additionally, affected individuals may produce abnormally low levels of proteins called antibodies (or immunoglobulins), particularly immunoglobulin G (IgG). Antibodies help protect the body against infection by foreign particles and germs. A reduction in antibodies can make it difficult for affected individuals to fight infections.

Some people with ALG1-CDG have physical abnormalities such as a small head size (microcephaly); unusual facial features; joint deformities called contractures; long, slender fingers and toes (arachnodactyly); or unusually fleshy pads at the tips of the fingers and toes. Eye problems that may occur in people with this condition include eyes that do not point in the same direction (strabismus) or involuntary eye movements (nystagmus). Rarely, affected individuals develop vision loss.

Less common abnormalities that occur in people with ALG1-CDG include respiratory problems, reduced sensation in their arms and legs (peripheral neuropathy), swelling (edema), and gastrointestinal difficulties.

The signs and symptoms of ALG1-CDG are often severe, with affected individuals surviving only into infancy or childhood. However, some people with this condition are more mildly affected and survive into adulthood.

Causes and biological mechanisms

From: MedlinePlus Genetics, National Library of Medicine

Mutations in the ALG1 gene cause ALG1-CDG. This gene provides instructions for making an enzyme that is involved in a process called glycosylation. During this process, complex chains of sugar molecules (oligosaccharides) are added to proteins and fats (lipids). Glycosylation modifies proteins and lipids so they can fully perform their functions. The enzyme produced from the ALG1 gene transfers a simple sugar called mannose to growing oligosaccharides at a particular step in the formation of the sugar chain. Once the correct number of sugar molecules are linked together, the oligosaccharide is attached to a protein or lipid.

ALG1 gene mutations lead to the production of an abnormal enzyme with reduced activity. The poorly functioning enzyme cannot add mannose to sugar chains efficiently, and the resulting oligosaccharides are often incomplete. Although the short oligosaccharides can be transferred to proteins and fats, the process is not as efficient as with the full-length oligosaccharide. The wide variety of signs and symptoms in ALG1-CDG are likely due to impaired glycosylation of proteins and lipids that are needed for normal function of many organs and tissues.

Inheritance and family implications

From: MedlinePlus Genetics, National Library of Medicine

This condition is inherited in an autosomal recessive pattern, which means both copies of the gene in each cell have mutations. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition.

How common is it?

From: MedlinePlus Genetics, National Library of Medicine

ALG1-CDG appears to be a rare disorder; fewer than 30 affected individuals have been described in the scientific literature.

Which doctor should you see?

The suggested department for discussing ALG1-congenital disorder of glycosylation is Clinical Genetics, with a clinical geneticist as the relevant type of clinician. Paediatrician (children) or physician (adults), with clinical geneticist referral.

This is an editorial referral starting point. The appropriate clinic depends on the person’s age, symptoms, previous diagnosis and local services. The first clinician can decide whether another specialty or a team is needed; a department label does not confirm the diagnosis.

How to prepare for an assessment

Bring a short timeline of the main symptoms: when they first appeared, whether they are constant or episodic, what seems to change them, and how they affect daily activities. Include previous reports, discharge summaries, current medicines and supplements, allergies, and any relevant family history. A dated record is more useful than trying to match every feature in an online article.

Ask the clinician what is already established and what remains uncertain. If a test is suggested, ask what question it answers, what its limitations are and how the result would change the next step. The information here is not an instruction to arrange every possible test. In children, bring growth, developmental and school information if it is relevant to the concern.

• Does the exact genetic or chromosome finding explain the observed features?
• Would a genetic counsellor help the family understand the result?
• Which organ-specific assessments are appropriate for this particular diagnosis?

Treatment discussions and follow-up

Where the source describes treatments, these are an overview of possible care, not a prescription for an individual. Ask which option applies to the confirmed diagnosis, what benefit is expected, what adverse effects to watch for and how progress will be assessed. Availability, approvals and local practice can differ from the country described in the source.

Before leaving the appointment, clarify the next review date, who will communicate results, and whom to contact if the situation changes. Discuss difficulties with sleep, work, school, mobility, eating or emotional wellbeing when these are relevant. Practical support may require coordination between the treating clinician and other services.

The collected references do not establish a complete prevention or long-term outlook section for this entry. Missing information should not be interpreted as proof that prevention is impossible or that a particular outcome is inevitable. Ask what is known for the exact subtype, stage and personal circumstances, and which uncertainties remain.

When to seek emergency help

Severe breathing difficulty, collapse, new stroke-like symptoms, a seizure that is prolonged or repeated without recovery, uncontrolled major bleeding, or an immediate risk of self-harm require emergency help. In India, call 112 or reach the nearest emergency department. This is a general, non-exhaustive warning list; it is not a condition-specific triage tool.