National Referral Laboratory

Test Panels and Screens

The National Referral Laboratory performs a number of biochemical analyses, including enzyme assay panels, in order to screen for a number of disorders at the one time. Positive results should be followed up by testing to determine or confirm the specific disorder.

This page contains information on the following screens and panels:

• Lysosomal Enzyme Panel (Neurolipidosis screen, White Cell Enzymes)
• Very long chain fatty acid analysis
• Phytanic acid analysis (+ pristanic acid)
• Urine mucopolysaccharide screen
• Urine oligosaccharide screen
• Transferrin isoform analysis

Lysosomal Enzyme Panel (Neurolipidosis screen, White Cell Enzymes)

The lysosomal enzyme panel tests for a range of lysosomal storage disorders (see below), with many showing overlapping clinical presentations. Note that this panel does not include testing for the mucopolysaccharidoses (MPS disorders).

The panel can be performed on either blood or cultured cells. For blood, we ask for 10mL EDTA blood, shipped at room temperature to be received by the National Referral Laboratory within 36 hours of collection. Greater shipping times can lead to the deterioration of a number of the enzymes, causing false positive results. It can also lead to a significantly reduced yield of leucocytes. The minimum volume for the full panel is 6mL. Smaller samples (minimum volume 3mL) can only be used for half of the enzyme panel and we will require a second sample for completion of the panel.

In blood, the panel includes 13 leucocyte enzyme assays and 2 plasma enzyme assays. It is able to detect patients affected by the following disorders:

• GM1-gangliosidosis
• GM2-gangliosidosis type 1 (Tay-Sachs disease, b-hexosaminidase A deficiency)
• GM2-gangliosidosis type 2 (Sandhoff disease)
• Metachromatic leucodystrophy
• Krabbe disease
• Gaucher disease
• Niemann-Pick disease type A and B
• Acid lipase deficiency (Wolman disease, cholesterol ester storage disease)
• Fucosidosis
• a-Mannosidosis
• MPS-VII (Sly syndrome)
• Mucolipidosis type II (I-cell disease)
• Mucolipidosis type III (Pseudo-Hurler polydystrophy)
• Ceroid lipofuscinosis neuronal type 1 (infantile NCL)
• Ceroid lipofuscinosis neuronal type 2 (late-infantile NCL)
• Galactosialidosis
• Schindler's disease

Very long chain fatty acid analysis

Very long chain fatty acid analysis is used for the detection of a range of peroxisomal disorders. This includes X-linked adrenoleucodystrophy (ALD), X-linked adrenomyeloneuropathy (AMN), peroxisomal biogenesis disorders of the Zellweger spectrum (Zellweger syndrome, neonatal ALD and infantile Refsum disease) and isolated disorders of peroxisomal b-oxidation (D-bifunctional protein deficiency, acyl-CoA oxidase deficiency).

This analysis can be performed on EDTA plasma, Li-heparin plasma or serum. Note that we are able to use plasma from an EDTA blood sample sent for the lysosomal enzyme panel. The minimum volume for analysis is 2mL. This testing can also be performed on cultured cells.

Phytanic acid analysis (+ pristanic acid analysis)

Phytanic acid analysis is also used for the detection of a number of peroxisomal disorders. It is elevated in Refsum disease, rhizomelic chondrodysplasia punctata (RCDP) and peroxisomal biogenesis disorders of the Zellweger spectrum (Zellweger syndrome, neonatal ALD and infantile Refsum disease).

It is important to note that phytanic acid is derived from the diet and will be normal in affected patients for the first few months of life. For the first 6 months of life, we recommend that plasmalogen analysis be used in place of phytanic acid for the diagnosis of infants suspected of RCDP.

Pristanic acid analysis, which is performed qualitatively, is used principally in the diagnosis of a-methylacyl CoA racemase deficiency and is often useful in the characterisation of peroxisomal disease.

Phytanic acid and pristanic acid analyses can be performed on EDTA plasma, Li-heparin plasma or serum. Note that we are able to use plasma from an EDTA blood sample sent for the lysosomal enzyme panel. The minimum volume for analysis is 2mL.

Urine mucopolysaccharide screen

This analysis is performed as the first stage in the diagnosis of the mucopolysaccharidoses (includes Hurler syndrome, Hunter syndrome, Sanfilippo syndrome, Morquio syndrome, Maroteaux-Lamy syndrome and Sly syndrome). Positive results are then followed by specific enzyme assays.

We require at least 15mL of urine (preferably an early morning sample). This can be sent frozen, freeze-dried or on filter paper.

Note that a urine mucopolysaccharide screen is required before we will proceed with enzyme testing for the mucopolysaccharidoses.

Urine oligosaccharide screen

The oligosaccharide screen is able to detect lysosomal storage disorders that result in the excretion of elevated levels of oligosaccharides. Positive results are then followed by specific enzyme assays.

We require at least 15mL of urine (preferably an early morning sample). This can be sent frozen, freeze-dried or on filter paper.

The oligosaccharide screen is able to detect patients affected by:

• GM1-gangliosidosis
• Galactosialidosis
• Sialidosis (Mucolipidosis I, neuraminidase deficiency)
• Mucolipidosis type II (I-cell disease)
• Mucolipidosis type III (Pseudo-Hurler polydystrophy)
• Fucosidosis
• a-Mannosidosis
• Aspartylglucosaminuria

Transferrin isoform analysis

Transferrin isoform analysis is used to detect patients affected by a congenital disorder of N-glycosylation (CDG). These are caused by a deficiency in one of at least 20 different enzymes. In patients with a positive transferrin isoform result, we are able to perform enzyme analysis for CDG types Ia and Ib only.

Note that there is one reported case where the transferrin isoform pattern was normal in an affected baby for the first six weeks of life. Any normal result obtained in a neonate should be repeated when the baby is at least 2 months of age.

For transferrin isoform analysis we require at least 500mL of serum or Li-heparin plasma. Note that EDTA plasma is not suitable.

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