NGLY1-congenital disorder of deglycosylation

What it is, symptoms and effects

From: MedlinePlus Genetics, National Library of Medicine

NGLY1-congenital disorder of deglycosylation (NGLY1-CDDG) is an inherited condition that affects many parts of the body. The severity of the signs and symptoms varies widely among people with the condition.

Individuals with NGLY1-CDDG typically develop features of the condition during infancy. They often have delayed development of speech and motor skills, such as sitting and walking, and weak muscle tone (hypotonia). Many affected individuals have movement abnormalities, such as uncontrolled movements of the limbs (choreoathetosis), and some develop seizures that are difficult to treat. Individuals with NGLY1-CDDG may also have problems with liver function. Some affected individuals have eye abnormalities, including degeneration of the nerves that carry information from the eyes to the brain (optic atrophy) and changes in the light-sensing tissue at the back of the eye (the retina). A reduction or absence of tears (hypolacrima or alacrima) is a common feature of NGLY1-CDDG.

Causes and biological mechanisms

From: MedlinePlus Genetics, National Library of Medicine

NGLY1-CDDG is caused by mutations in the NGLY1 gene. The enzyme produced from this gene, called N-glycanase 1, helps cells get rid of abnormal proteins. It removes chains of sugars (glycans) from misfolded proteins through a process called deglycosylation, which is thought to be an essential step for certain abnormal proteins to be broken down. The gene mutations that cause NGLY1-CDDG impair production of the N-glycanase 1 enzyme, resulting in a severe reduction or absence of the enzyme's function. Without the removal of glycans, the misfolded proteins cannot be broken down. It is thought that the abnormal proteins accumulate and form clumps (aggregates) in cells. These aggregates may damage cells in the brain, liver, and eyes, leading to the signs and symptoms of NGLY1-CDDG.

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

NGLY1-CDDG is a rare disorder. At least 46 individuals with the condition have been described in the medical literature.

Understanding terms used in the source

These definitions explain medical words used above. A definition is not evidence that another condition is present, and it does not predict how a symptom will develop. Ask the clinician which terms apply to the actual examination or test result.

Choreoathetosis

Involuntary movements characterized by both athetosis (inability to sustain muscles in a fixed position) and chorea (widespread jerky arrhythmic movements).

Optic atrophy

Atrophy of the optic nerve. Optic atrophy results from the death of the retinal ganglion cell axons that comprise the optic nerve and manifesting as a pale optic nerve on fundoscopy.

Hypotonia

Hypotonia is an abnormally low muscle tone (the amount of tension or resistance to movement in a muscle). Even when relaxed, muscles have a continuous and passive partial contraction which provides some resistance to passive stretching. Hypotonia thus manifests as diminished resistance to passive stretching. Hypotonia is not the same as muscle weakness, although the two conditions can co-exist.

Affected

This term applies to a family member who is diagnosed with the same condition as the individual who is the primary focus of investigation (the proband).

Alacrima

The complete absence of aqueous tear production. Typically, this is clinically measured by a Schirmer I test result of 0 millimeters of wetting on the filter paper strip after 5 minutes.

Which doctor should you see?

The suggested department for discussing NGLY1-congenital disorder of deglycosylation 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.