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Test ID: UPGC
Uroporphyrinogen III Synthase (Co-Synthase) (UPG III S), Erythrocytes

Useful For Suggests clinical disorders or settings where the test may be helpful

Ruling in or ruling out congenital erythropoietic porphyria

Genetics Test Information Provides information that may help with selection of the correct test or proper submission of the test request

This test measures UPG III synthase to confirm congenital erythropoietic porphyria. It does not measure UPG I synthase, the enzyme deficient in acute intermittent porphyria (AIP). For AIP (and UPG I synthase), order PBGD_/88925 Porphobilinogen (PBG) Deaminase, Erythrocytes.

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

Congenital erythropoietic porphyria (CEP) is an extremely rare and severe porphyria that typically begins in early infancy. Also known as Gunther disease, CEP results from a deficiency of uroporphyrinogen III (co-) synthase (Upg III S). In most cases the disorder is suggested during the first few days or weeks of life by pink, violet, or brown urinary staining of diapers. A few cases of adult-onset CEP have been reported. Clinical symptoms include hemolytic anemia, hepatosplenomegaly, skin photosensitivity, scarring and blistering, red or brown dental discoloration (erythrodontia), and hypertrichosis (excess body hair). Growth and cognitive developmental delays are commonly observed in individuals with CEP. CEP is transmitted as an autosomal recessive trait.

 

See Porphyria (Acute) Testing Algorithm and Porphyria (Cutaneous) Testing Algorithm in Special Instructions.

Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.

> or =75 Relative Units (normal)

See The Heme Biosynthetic Pathway in Special Instructions.

Interpretation Provides information to assist in interpretation of the test results

Circulating red cells normally contain high levels of activity of Upg III S, and the diminished activity associated with congenital erythropoietic porphyria (CEP) is readily demonstrable by incubation of red cells from an affected person.

 

Values for Upg III S <75 Relative Units are suggestive of a biochemical diagnosis of CEP. This test does not reliably distinguish between individuals with heterozygous Upg III S deficiency and normal individuals.

Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

This test is not useful for ruling out acute intermittent porphyria (AIP) a disorder caused by decreased uroporphyrinogen I synthase (also known as porphobilinogen deaminase). For AIP, order PBGD_/88925 Porphobilinogen (PBG) Deaminase, Whole Blood.

 

If possible, specimens from patients suspected of having CEP should be drawn prior to blood transfusions; Upg III S activity in transfused erythrocytes can cause false-negative results.

 

Abstinence from alcohol is essential for at least 24 hours. While the effects of alcohol on this enzyme have not yet been determined, alcohol is known to suppress or induce other enzymes in the heme biosynthetic pathway.

 

It is essential to proceed expeditiously with obtaining, processing, and dispatching the specimen, precisely following the procedures specified in the Specimen Requirements and paying special heed to maintaining low temperatures. Failure to do so will allow enzyme degradation, resulting in falsely low values (ie, false-positive results).

Clinical Reference Provides recommendations for further in-depth reading of a clinical nature

1. Ellefson RD: Porphyrinogens, porphyrins, and the porphyrias. Mayo Clin Proc 1982;57:454-458

2. Doss MO, Kuhnel A, Gross U: Alcohol and porphyrin metabolism. Alcohol Alcohol 2000;35(2):109-125

3. Desnick RJ, Astrin KH: Congenital erythropoietic porphyria: advances in pathogenesis and treatment. Br J Haematol 2002;117(4):779-795

Special Instructions and Forms Describes specimen collection and preparation information, test algorithms, and other information pertinent to test. Also includes pertinent information and consent forms to be used when requesting a particular test