ALPHA N ACETYL GLUCOSAMINIDASE

The ALPHA N ACETYL GLUCOSAMINIDASE test measures the activity of alpha-N-acetylglucosaminidase, a lysosomal enzyme also known as NAGLU. This enzyme helps break down heparan sulfate, a complex molecule naturally found in the body. Significantly reduced NAGLU activity is associated with mucopolysaccharidosis type IIIB, commonly called Sanfilippo syndrome type B. This is a rare inherited lysosomal storage disorder in which partially broken-down heparan sulfate accumulates within cells and progressively affects the nervous system and other parts of the body.

Children with Sanfilippo syndrome may appear healthy at birth and during early childhood. Symptoms often develop gradually, and the condition can initially resemble common developmental or behavioural disorders. Measuring NAGLU enzyme activity can provide important biochemical evidence and guide confirmatory molecular testing. Early identification helps families obtain appropriate specialist care, genetic counselling and supportive management.

Benefits of the Test

• Measures alpha-N-acetylglucosaminidase enzyme activity.
• Helps diagnose Sanfilippo syndrome type B or MPS IIIB.
• Supports investigation of unexplained developmental or behavioural changes.
• Helps distinguish MPS IIIB from other mucopolysaccharidoses and neurological disorders.
• Provides biochemical evidence that can guide NAGLU gene analysis.
• May assist with targeted family testing after a diagnosis is confirmed.

Why Doctors Recommend This Test

A paediatrician, neurologist, clinical geneticist or metabolic specialist may recommend this test when a child has features suggestive of Sanfilippo syndrome. Possible findings include delayed speech or development, progressive loss of previously acquired abilities, hyperactivity, difficulty concentrating, sleep disturbance, behavioural changes, seizures, problems with walking, reduced coordination or gradual intellectual decline. Some children may also have recurrent respiratory or ear infections, hearing impairment, coarse hair, thick eyebrows, diarrhoea, enlarged liver or spleen, joint stiffness or subtle facial changes.

The early symptoms are not specific to MPS IIIB and may overlap with autism spectrum disorder, attention-related conditions and other genetic or neurological diseases. Doctors therefore use enzyme testing together with clinical assessment, urinary glycosaminoglycan analysis and genetic testing. Demonstrating markedly reduced NAGLU activity supports MPS IIIB, while molecular analysis of the NAGLU gene is generally used to confirm the diagnosis.

Preparation Before Test

Fasting is usually not required unless the doctor or laboratory gives specific instructions. Inform the healthcare team about current medicines, supplements, recent blood transfusions and any known family history of mucopolysaccharidosis, developmental disorders or unexplained childhood neurological disease. Depending on the validated laboratory method, testing may use leukocytes, plasma, cultured skin fibroblasts or a dried blood spot. Accurate collection, transportation and temperature control are important because improper handling can affect enzyme activity.

Normal Reporting Time

This is a specialized enzyme assay and generally requires several working days or longer. The exact reporting time depends on the specimen type, sample transportation, testing schedule, quality-control procedures and whether repeat or confirmatory analysis is required. Focus Diagnostics will provide the applicable turnaround estimate during sample collection.

Who Should Take This Test?

• Children with unexplained developmental delay or loss of acquired abilities.
• Patients with progressive behavioural, neurological or sleep-related abnormalities.
• Individuals with abnormal urinary glycosaminoglycan screening results.
• People with a family history of MPS IIIB or known NAGLU gene variants.
• Siblings or relatives of a person with confirmed Sanfilippo syndrome type B.
• Patients referred by a geneticist, neurologist or metabolic specialist.

Detailed Information

MPS IIIB is caused by disease-causing variants in the NAGLU gene and follows an autosomal recessive inheritance pattern. An affected person generally inherits one altered gene copy from each parent. Parents with one altered copy are usually healthy carriers. When both parents are carriers, each pregnancy has a 25% probability of an affected child, a 50% probability of a carrier child and a 25% probability of a child who inherits neither familial variant.

Very low NAGLU enzyme activity can support the diagnosis, but results must be interpreted according to the laboratory's method, specimen type and reference interval. An abnormal result may be followed by NAGLU gene sequencing and other molecular studies. Doctors may also request urine glycosaminoglycan testing, neurological assessment, developmental evaluation, hearing tests, eye examination, imaging or other investigations. A normal or borderline result should be reviewed carefully when clinical suspicion remains high because sample quality and technical factors can influence enzyme measurements.

Management of MPS IIIB is individualized and usually involves a multidisciplinary team. Care may include behavioural and sleep support, seizure control, physiotherapy, nutritional care, hearing management, respiratory care and developmental services. Research into disease-specific treatments continues, but treatment decisions should be discussed with a specialist familiar with inherited metabolic disorders. Genetic counselling can help families understand inheritance, carrier testing, testing of relatives and available reproductive options.