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Unit Code 83638:
Galactose, Quantitative, Plasma

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Useful For

Screening for galactosemia

Clinical Information

Galactosemia is an inborn error of galactose metabolism caused

by a deficiency of 1 of 3 enzymes: galactose-1-phosphate

uridyltransferase (GALT), galactokinase (GK), and uridine diphosphate

galactose -4-epimerase (UDPGal-4-epimerase). In patients with

galactosemia, consumption of milk products results in exaggerated

plasma galactose concentrations (dietary lactose is metabolized

to glucose and galactose).

                                                                                                                                                                                

The most common cause of galactosemia is deficiency of GALT.

Symptoms of untreated GALT deficiency include failure to thrive,

vomiting, liver disease, cataracts, and developmental delay.

Patients with classic GALT deficiency are at risk of life-threatening

liver and kidney failure and Escherichia coli sepsis in the newborn

period. Because of the poor prognosis of the untreated galactosemic

patient, it is imperative that treatment be instituted early. This led

to the inclusion of GALT deficiency into all newborn screening

programs in the United States. Accordingly, most patients are

diagnosed following a positive newborn screen, but physicians

must still consider this diagnosis in any patient presenting with

liver disease.

 

Galactosemia is diagnosed by specific enzyme assay when the

clinical presentation is highly suggestive of a specific deficiency

or by screening for abnormally accumulating metabolites, in

particular galactose and galactose-1-phosphate (G-1-P).

The following table indicates which metabolites are elevated

in the various forms of galactosemia as long as the patient is

on a regular, lactose-containing diet:

 

                                      Galactose                  G-1-P

Deficiency              (plasma/urine)        (blood)

Galactokinase         Elevated                        Normal

                                                                               

GALT                           Elevated                        Elevated

 

UDPGal-4-                 Normal-                          Elevated

Epimerase                Elevated

 

Molecular testing for the most common galactosemia alleles and

variants is available to confirm the patient's genotype (#84360

"Galactosemia Confirmation Test”, #84366 "Galactosemia

Confirmation Test, Blood”).

Reference Values

1-7 days:              <5.4 mg/dL

8-14 days:            <3.6 mg/dL

>14 days:             <2.0 mg/dL

Interpretation

Elevated plasma galactose values are found in individuals with

galactosemia.

 

When elevated, the specific enzymatic defect should be

determined. In order of probability they are: #8333 "Galactose-1-

Phosphate Uridyltransferase (GALT), Blood”; or #8628 "Galactokinase,

Blood”; galactose-4-epimerase (rare; referral test). #84360

"Galactosemia Confirmation Test, Blood ” which includes GALT

and reflexes to molecular testing, is the preferred second-order

diagnostic test.

 

 

Cautions

 For monitoring of dietary compliance refer to #80337 "Galactose-1-Phosphate,

(Gal-1-P), Erythrocytes".

Clinical Reference

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

      Metabolic and Molecular Bases of Inherited Disease.

      8th edition. Edited by CR Scriver, AL Beaudet, D Valle, et al:

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

 

2.   Prinz W, Meldrum W, Wilkinson L:  A simple and rapid

      thin-layer chromatographic method for the identification

      of urinary carbohydrates. Clin Chim Acta 1978;82:229-232

 

3.   Shin YS:  Galactose metabolites and disorders of

      galactose metabolism. In Techniques in Diagnostic

      Human Biochemical Genetics. Edited by FA Holmes.

      New York, Wiley-Liss, 1991, pp 267-283

Key