Alpha-N-acetylgalactosaminidase deficiency

What it is, symptoms and effects

From: MedlinePlus Genetics, National Library of Medicine

Alpha-N-acetylgalactosaminidase deficiency, also known as Schindler disease, is an inherited disorder that can affect the development of the nervous system. People with alpha-N-acetylgalactosaminidase deficiency often have distinctive facial features that can be described as "coarse" and tooth abnormalities such as widely-spaced teeth and missing teeth (hypodontia).

The three types of alpha-N-acetylgalactosaminidase deficiency differ in the severity of their signs and symptoms and the age at which they first appear. The signs and symptoms of alpha-N-acetylgalactosaminidase deficiency can vary, even among members of the same family.

Type I is the most severe form of this condition. Babies with alpha-N-acetylgalactosaminidase deficiency type I appear healthy at birth. However, by late infancy, these babies typically have trouble meeting normal developmental milestones. By the age of 2 years, individuals with type I begin to lose skills that they had already acquired (developmental regression). Individuals with type I often experience weak muscle tone (hypotonia), vision and hearing loss, and seizures. During early childhood, children with type I typically lose awareness of their surroundings and eventually become unresponsive.

Alpha-N-acetylgalactosaminidase deficiency type II is the least severe form. Type II is typically diagnosed in adulthood. Affected individuals may have mild cognitive impairment and hearing loss caused by abnormalities of the inner ear (sensorineural hearing loss). They may also experience a loss of sensation or muscle weakness in the extremities (peripheral neuropathy). Clusters of enlarged blood vessels that form small, dark red spots on the skin (angiokeratomas) are a characteristic feature of alpha-N-acetylgalactosaminidase deficiency type II.

Type III is the intermediate form of alpha-N-acetylgalactosaminidase deficiency. People with type III may show a variety of signs and symptoms, including developmental, speech, and language delays; seizures that begin in infancy; and features of autism spectrum disorder that appear in childhood. Autism spectrum disorder is characterized by impaired communication and socialization skills. People with type III may also have skeletal signs and symptoms, such as pain in the lower back, hips, and knees. Wear on the cartilage (disks) and bones of the neck (cervical spondylosis) and a cyst-like collection of cerebrospinal fluid that forms in the spinal cord (syringohydromyelia) have also been reported.

Causes and biological mechanisms

From: MedlinePlus Genetics, National Library of Medicine

Variants (also called mutations) in the NAGA gene cause alpha-N-acetylgalactosaminidase deficiency. The NAGA gene provides instructions for making the enzyme alpha-N-acetylgalactosaminidase. This enzyme works in the lysosomes, which are compartments within cells that digest and recycle materials. Alpha-N-acetylgalactosaminidase helps break down complexes called glycoproteins and glycolipids, which consist of sugar molecules attached to certain proteins and fats.

Variants in the NAGA gene can alter the alpha-N-acetylgalactosaminidase enzyme and interfere with the breakdown of glycoproteins and glycolipids. As these substances accumulate in the lysosomes, they can cause cells to malfunction and eventually die. Cell damage in the nervous system and other tissues and organs of the body leads to the signs and symptoms seen in people with alpha-N-acetylgalactosaminidase deficiency.

Researchers are studying why some people with NAGA gene variants have severe signs and symptoms, while others with the same gene variant have milder features or no features at all.

Conditions that cause molecules to build up inside lysosomes, such as alpha-N-acetylgalactosaminidase deficiency, belong to a large family of lysosomal storage disorders.

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 must have a variant to cause the disorder. 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

Alpha-N-acetylgalactosaminidase deficiency is very rare. Fewer than 50 individuals with this condition have been reported in the medical literature. Some cases of alpha-N-acetylgalactosaminidase deficiency likely remain undiagnosed.

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.

Blindness · Very frequent (99-80%)

Blindness is the condition of lacking visual perception defined as a profound reduction in visual perception. On the 6m visual acuity scale, blindness is defined as less than 3/60. On the 20ft visual acuity scale, blindness is defined as less than 20/400. On the decimal visual acuity scale, blindness is defined as less than 0.05. Blindness is typically characterized by a visual field of no greater than 10 degrees in radius around central fixation.

Developmental regression · Very frequent (99-80%)

Loss of developmental skills, as manifested by loss of developmental milestones.

Global developmental delay · Very frequent (99-80%)

A delay in the achievement of motor or mental milestones in the domains of development of a child, including motor skills, speech and language, cognitive skills, and social and emotional skills. This term should only be used to describe children younger than five years of age.

Hearing impairment · Very frequent (99-80%)

A decreased magnitude of the sensory perception of sound.

Hypotonia · Very frequent (99-80%)

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.

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.

Oligosacchariduria · Very frequent (99-80%)

Increased urinary excretion of oligosaccharides (low molecular weight carbohydrate chains composed of at least three monosaccharide subunits), derived from a partial degradation of glycoproteins.

Spasticity · Very frequent (99-80%)

A motor disorder characterized by a velocity-dependent increase in tonic stretch reflexes with increased muscle tone, exaggerated (hyperexcitable) tendon reflexes.

Other findings in the same source

From: Orphanet

Additional reported features include Cataract (Frequent (79-30%)); Cerebellar hypoplasia (Frequent (79-30%)); Cerebral cortical atrophy (Frequent (79-30%)); Clonus (Frequent (79-30%)); Coarse facial features (Frequent (79-30%)); Nystagmus (Frequent (79-30%)); Peripheral neuropathy (Frequent (79-30%)); Seizure (Frequent (79-30%)); Tetraplegia (Frequent (79-30%)); Vertigo (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 Alpha-N-acetylgalactosaminidase deficiency 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 Alpha-N-acetylgalactosaminidase deficiency. 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.