Aspartylglucosaminuria

What it is, symptoms and effects

From: MedlinePlus Genetics, National Library of Medicine

Aspartylglucosaminuria is a condition that primarily affects mental functioning and movement. This conditions worsens over time. Infants with aspartylglucosaminuria appear healthy at birth, and development is typically normal throughout early childhood. Around the age of 2 or 3, affected children usually begin to have delayed speech, mild intellectual disability, and problems coordinating movements. Other features that develop in childhood include respiratory infections, a protrusion of organs through gaps in muscles (hernia), and a growth spurt resulting in a large head size (macrocephaly).

Intellectual disability and movement problems worsen in adolescence. Most people with this disorder lose much of the speech they have learned, and affected adults usually have only a few words in their vocabulary. Adults with aspartylglucosaminuria often have psychological disorders and may develop seizures.

People with aspartylglucosaminuria may also have bones that become progressively weak and prone to fracture (osteoporosis), an unusually large range of joint movement (hypermobility), and loose skin. Affected individuals tend to have a characteristic facial appearance that includes widely spaced eyes (ocular hypertelorism), small ears, and full lips. The nose is short and broad and the face is usually square-shaped. They often have poor oral health, including infections and gum disease (gingivitis). Children with this condition may be tall for their age, but lack of a growth spurt in puberty typically causes adults to be short with a small head size (microcephaly). Individuals with aspartylglucosaminuria usually survive into mid-adulthood.

Causes and biological mechanisms

From: MedlinePlus Genetics, National Library of Medicine

Variants (also known as mutations) in the AGA gene cause aspartylglucosaminuria. The AGA gene provides instructions for producing an enzyme called aspartylglucosaminidase. This enzyme is active in lysosomes, which are structures inside cells that act as recycling centers. Within lysosomes, the enzyme helps break down complex chains of sugar molecules (oligosaccharides) attached to certain proteins (glycoproteins).

AGA gene variants result in a lack (deficiency) of the aspartylglucosaminidase enzyme in lysosomes, preventing the normal breakdown of glycoproteins. As a result, glycoproteins can build up within the lysosomes. Excess glycoproteins disrupt the normal functions of the cell and can result in cell death. A buildup of glycoproteins seems to particularly affect nerve cells in the brain; loss of these cells causes many of the signs and symptoms of aspartylglucosaminuria.

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 variants. The parents of an individual with an autosomal recessive condition each carry one copy of the altered gene, but they typically do not show signs and symptoms of the condition.

How common is it?

From: MedlinePlus Genetics, National Library of Medicine

In Finland, it is estimated that 1 to 3 individuals are born with aspartylglucosaminuria each year. This condition is less common outside of Finland, but the incidence is unknown.

Reported clinical features and what the terms mean

The following findings are associated with this condition in Orphanet. They are not a checklist for diagnosing yourself, and they do not all occur in every affected person. Some are examination, imaging or laboratory findings that cannot be recognised at home.

The frequency labels describe how often a finding was reported among people with the condition in the source. They do not give the chance that a person with that symptom has the condition. Definitions below reproduce HPO terminology; they explain the term, not the likely severity in an individual.

Abnormal facial shape · Very frequent (99-80%)

An abnormal morphology (form) of the face or its components.

Abnormality of amino acid metabolism · Very frequent (99-80%)

Abnormality of an amino acid metabolic process.

Abnormality of speech or vocalization · Very frequent (99-80%)

An abnormality in the sound (volume) or cadence (rate) of speech.

Aspartylglucosaminuria · Very frequent (99-80%)

Excretion of excess amounts of aspartylglucosamine in the urine.

Delayed speech and language development · Very frequent (99-80%)

A degree of language development that is significantly below the norm for a child of a specified age.

Dyskinesia · Very frequent (99-80%)

A movement disorder which consists of effects including diminished voluntary movements and the presence of involuntary movements.

Gingival overgrowth · Very frequent (99-80%)

Hyperplasia of the gingiva (that is, a thickening of the soft tissue overlying the alveolar ridge. The degree of thickening ranges from involvement of the interdental papillae alone to gingival overgrowth covering the entire tooth crown.

Hypertelorism · Very frequent (99-80%)

Interpupillary distance more than 2 SD above the mean (alternatively, the appearance of an increased interpupillary distance or widely spaced eyes).

Intellectual disability · Very frequent (99-80%)

The term intellectual disability or intellectual developmental disorder is used to describe significantly sub-average intellectual and adaptive functioning based on clinical assessment and as measured by individually administered, appropriately normed, standardized and validated tests of intellectual functioning and adaptive behavior, with onset during the developmental period from infancy through adolescence.

Mandibular prognathia · Very frequent (99-80%)

Abnormal prominence of the chin related to increased length of the mandible.

Microtia · Very frequent (99-80%)

Underdevelopment of the external ear.

Scoliosis · Very frequent (99-80%)

The presence of an abnormal lateral curvature of the spine.

Short nose · Very frequent (99-80%)

Distance from nasion to subnasale more than two standard deviations below the mean, or alternatively, an apparently decreased length from the nasal root to the nasal tip.

Thick vermilion border · Very frequent (99-80%)

Increased width of the skin of vermilion border region of upper lip.

Other findings in the same source

From: Orphanet

Additional reported features include Umbilical hernia (Very frequent (99-80%)); Wide nasal bridge (Very frequent (99-80%)); Large face (Very frequent (99-80%)); Abnormal cortical bone morphology (Frequent (79-30%)); Abnormal morphology of ulna (Frequent (79-30%)); Abnormality of the dentition (Frequent (79-30%)); Anterior beaking of lumbar vertebrae (Frequent (79-30%)); Carious teeth (Frequent (79-30%)); Coarse facial features (Frequent (79-30%)); Macroglossia (Frequent (79-30%)). This is a selected summary, not a complete description of the condition.

Which doctor should you see?

The suggested department for discussing Aspartylglucosaminuria is Metabolic Medicine, with a metabolic specialist / clinical geneticist as the relevant type of clinician. Paediatrician (children) or physician (adults), with metabolic specialist / 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.

• Is a biochemical or molecular result needed to clarify the diagnosis?
• Does this condition require an individual plan for illness or reduced food intake?
• Should nutrition advice come from a specialist metabolic dietitian?

Treatment discussions and follow-up

The material gathered for this draft does not provide a complete condition-specific treatment pathway for Aspartylglucosaminuria. That gap does not mean that treatment is unavailable. A clinician needs to establish the diagnosis and review current guidance before recommending medicines, procedures, rehabilitation or other support.

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.