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Unit Code 80341:
Galactose-1-Phosphate Uridyltransferase Biochemical Phenotyping, Erythrocytes

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Useful For

Determining the exact biochemical phenotype when quantitative

GALT data suggests a GG or DG phenotype

 

A quantitative GALT level (#8333 "Galactose-1-Phosphate

Uridyltransferase [GALT], Blood") is used in addition to the

isoelectric focusing for accurate interpretation

 

Determining biochemical phenotypes of siblings, when parental

specimens are co-run for both quantitative and isoelectric focusing

banding data

Clinical Information

Galactosemia, an inborn error of metabolism disease, is most

commonly caused by galactose-1-phosphate uridyltransferase

(GALT) deficiency.

 

Most states perform heel-stick screening for GALT deficiency,

and if reduced galactose metabolism is detected, confirmation

tests are required.

 

The quantitative assay, which measures enzymatic activity,

provides an approximation of the biochemical phenotype (an

estimation of the expected genotype, such as GG, without identification

or prediction of specific mutations). There are 6 phenotypes generally

recognized by quantitation:

-  Normal-normal (NN)

-  Duarte heterozygote (ND)

-  Classic heterozygote (NG)

-  Duarte homozygote (DD)

-  Duarte galactosemia compound heterozygote (DG)

-  Galactosemia-galactosemia (GG)

 

It is important to distinguish GG from DG. GG patients must be on

galactose-free diets. DG patients must be monitored closely, and in

some cases, dietary treatment may be recommended. It is current

practice to maintain infants with a DG phenotype on a galactose-free

diet for 1 year.

 

Since quantitation can only approximate phenotypes, it becomes

important to differentiate specifically between DG and GG

biochemical phenotypes.

Reference Values

Descriptive report

Interpretation

There are a variety of biochemical phenotypes in galactosemia

and quantitative data is only suggestive of the phenotype for a

particular individual.

 

An interpretive report is provided.

 

See "Galactosemia Testing Algorithm" in Special Instructions

for additional information.

Cautions

The phenotype of a neonate can be arrived at with greater

confidence when the parents' phenotypes also are established. 

 

Since transfusion results in replacement of significant number of

red cells, the assay should be deferred for 90 days posttransfusion.

Special Instructions and Forms

• Galactosemia Testing Algorithm 

Clinical Reference

1.   Holton JB, Walter JH, Tyfield LA : Galactosemia. In The

      Metabolic and Molecular Basis of Inherited Disease. Vol 1. 8th

      edition. Edited by CR Scriver, AL Beaundet, WS Sly, et al. New York,

      McGraw-Hill Book Company, 2001, pp 1553-1587

 

2.   Walter JH, Collins JE, Leonard JV: Recommendations for the

      management of galactosemia. Arch Dis Child 1999 Jan;80(1):

      93-96

Key