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Test ID: AGXTG Alanine:Glyoxylate Aminotransferase (AGXT) Mutation Analysis (G170R), Blood

Useful For

Identifying patients with the pyridoxine responsive form of primary hyperoxaluria type 1 (PH1)

 

Determining the presence of the Gly170Arg (G170R) mutation in the AGXT gene

 

Carrier testing of at-risk family members

Method Name

Direct Mutation Analysis by Polymerase Chain Reaction (PCR)

Reporting Name

AGXT Mutation Analysis (G170R)

Specimen Type

Varies


Specimen Required


Specimen Type: Whole blood

Container/Tube:

Preferred: Lavender top (EDTA) or yellow top (ACD)

Acceptable: Any anticoagulant

Specimen Volume: 2 mL

Collection Instructions:

1. Invert several times to mix blood.

2. Send specimen in original tube.

Additional Information: Specimen preferred to arrive within 96 hours of draw.


Specimen Minimum Volume

0.5 mL

Specimen Stability Information

Specimen Type Temperature Time
Varies Ambient (preferred)
  Frozen 
  Refrigerated 

Clinical Information

Primary hyperoxaluria type 1 (PH1) is an autosomal recessive disorder in which excessive oxalates are formed by the liver and excreted by the kidneys, causing a wide spectrum of disease ranging from renal failure in infancy to mere renal stones in late adulthood. It is caused by deficiencies of the liver-specific peroxisomal enzyme AGXT (alanine-glyoxylate amino-transferase). The diagnosis may be suspected when clinical signs, increased urinary oxalate, glycolate, and glycerate excretion are present. Diagnostic confirmation requires the enzyme assay of the liver tissue, although this test is not readily available.

 

The toxicity of excess oxalate has been implicated in disease pathogenesis. Thus, treatment options have primarily centered on limiting oxalate ingestion and absorption. Pyridoxine (vitamin B[6]) has proven to be a promising therapeutic agent by increasing the concentration of cofactor involved in the metabolic reactions that decrease oxalate production. However, only 20% to 30% of patients have been known to be responsive to pyridoxine. Testing patients for pyridoxine responsiveness has been recommended at any stage of renal function, although assessment of pyridoxine responsiveness is not always easy to perform and diagnostic criteria have not been standardized. Recently, researchers at Mayo Clinic found that patients with a particular mutation (Gly170Arg) in the AGXT gene are responsive to the pyridoxine, while affected individuals without this mutation are not responsive.

Reference Values

An interpretive report will be provided.

Interpretation

Reported as negative or positive. The laboratory provides an interpretation of the results. This interpretation includes an overview of the results and their significance and a correlation to available clinical information.

Clinical Reference

1. Milosevic D, Rinat C, Batinic D, Frishberg Y: Genetic analysis-a diagnostic tool for primary hyperoxaluria type I. Pediatr Nephrol 2002 Nov;17(11):896-898

2. Pirulli D, Marangella M, Amoroso A: Primary hyperoxaluria: genotype-phenotype correlation. J Nephrol 2003 Mar-Apr;16(2):297-309

3. Amoroso A, Pirulli D, Florian F, et al: AGXT gene mutations and their influence on clinical heterogeneity of type I primary hyperoxaluria. J Am Soc Nephrol 2001 Oct;12(10):2072-2079

Day(s) and Time(s) Performed

Tuesday; 2 p.m.

Analytic Time

5 days

Test Classification

This test was developed and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. This test has not been cleared or approved by the U.S. Food and Drug Administration.

CPT Code Information

81479-Unlisted molecular pathology procedure

LOINC Code Information

Test ID Test Order Name Order LOINC Value
AGXTG AGXT Mutation Analysis (G170R) 69383-8

 

Result ID Test Result Name Result LOINC Value
53192 Result Summary 50397-9
53193 Result No LOINC Needed
53194 Interpretation 69047-9
53195 Specimen 31208-2
53196 Source 31208-2
53197 Released By No LOINC Needed

Forms

1. New York Clients-Informed consent is required. Please document on the request form or electronic order that a copy is on file. An Informed Consent for Genetic Testing (T576) is available in Special Instructions.

2. Molecular Genetics: Congenital Inherited Diseases Patient Information (T521) in Special Instructions

Mayo Medical Laboratories | Genetics and Pharmacogenomics Catalog Additional Information:

mml-inherited-molecular