Galactosemia: Galactose-1-Phosphate Analysis

Galactosemia is an inborn error of carbohydrate metabolism caused by the deficiency of galactose-1-phosphate uridyl transferase (GALT), which performs the second enzymatic step in the conversion of galactose to glucose-1-phosphate. As a result of the enzyme deficiency, excess galactose is excreted in the urine and the substrate for GALT, galactose-1-phosphate, accumulates throughout the body.

Turnaround Time

10 days

CPT Code(s)

84378

Cost

$200

• Galactosemia

Manifestations of the galactosemia appear within days of the initiation of milk feedings, and include vomiting, jaundice and failure to thrive. If left untreated for a prolonged period of time, patients will develop hepatomegaly, cataracts and intellectual disability. Speech delay and premature ovarian failure are also observed in many galactosemia patients, even in those who are diagnosed early and put on treatment.

Galactosemia is typically detected very early because of newborn screening programs, which measure GALT enzyme activity in dried blood spots. The measurement of galactose-1-phosphate is performed to confirm a new diagnosis of galactosemia and to periodically monitor the effectiveness of treatment in patients known to have the disease.

Galactose-1-phosphate (Gal-1-P) is measured by first converting endogenous galactose-1-phosphate to galactose using alkaline phosphatase, and then converting galactose to galactonolactone using ?-galactose dehydrogenase. During the second enzyme reaction, NAD is reduced to NADH, the accumulation of which can be measured using its absorbance at 340 nm. Results are reported in mg Gal-1-P / dL RBC.

Galactose-1-phosphate measurements must be performed in washed red blood cells. Collect 5 ml blood in a sodium heparin, green top tube. The laboratory will isolate red blood cells for use in the assay if a whole blood sample is sent.

Send via courier or 24-hour delivery at room temperature (not frozen). Red blood cells must be isolated within 24 hours of sample collection.