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Galactosemia is a disorder of carbohydrate metabolism caused by a deficiency of one of three enzymes (galactokinase, galactose-1-phosphate uridyltransferase, uridine diphosphate galactose-4-epimerase) involved in galactose metabolism. Classic galactosemia, the most common form, is caused by a deficiency of galactose-1-phosphate uridyltransferase (GALT) due to mutations in the GALT gene. Other rare forms of galactosemia may be caused by deficiencies of either galactokinase or galactose-4-epimerase.
Tests generally appear in the order most useful for common clinical situations
| Test name: Galactose-1-Phosphate Uridyltransferase |
| ARUP #: 0080125 |
| Methodology: Enzymatic |
| Use: Measure GALT enzyme activity to predict disease status |
| Limitations: Rare forms of galactosemia (caused by a deficiency of either galactokinase or galactose-4-epimerase) will not be detected Enzyme test can not predict GALT carrier status |
| Follow-up: GALT gene mutation analysis is recommended to determine the specific mutations in affected individuals |
| Test name: Galactosemia, (GALT) Enzyme Activity & 9 Mutations |
| ARUP #: 0051175 |
| Methodology: Enzymatic/Polymerase Chain Reaction/Single Nucleotide Extensions |
| Use: Clarify an abnormal newborn screen for galactosemia; test symptomatic neonates; carrier testing for parents of offspring deemed affected or a carrier of galactosemia Evaluates 9 common GALT gene mutations (Q188R, S135L, K285N, T138M, L195P, Y209C, IVS2-2 A>G, N314D and L218L) and measures GALT enzyme activity in red blood cells Clinical sensitivity approaches 80% in Caucasians; lower in other ethnic groups |
| Limitations: Test should not be used to monitor dietary compliance of affected individuals Only 9 common GALT mutations will be evaluated Rare forms of galactosemia (caused by a deficiency of either galactokinase or galactose-4-epimerase) will not be detected |
| Follow-up: If enzyme activity is in the affected range and 2 mutations are not detected, GALT gene sequencing is recommended to identify the causative mutations |
| Test name: Galactosemia, (GALT) 9 Mutations |
| ARUP #: 0051176 |
| Methodology: Polymerase Chain Reaction/Single Nucleotide Extensions |
| Use: Evaluates 9 common GALT gene mutations (Q188R, S135L, K285N, T138M, L195P, Y209C, IVS2-2 A>G, N314D and L218L) Clinical sensitivity approaches 80% in Caucasians; lower in other ethnic groups |
| Limitations: Only 9 common GALT mutations will be evaluated Rare forms of galactosemia (caused by a deficiency of either galactokinase or galactose-4-epimerase) will not be detected |
| Follow-up: If enzyme activity is in the affected range and 2 mutations are not detected, GALT gene sequencing is recommended to identify the causative mutations |
| Test name: Galactosemia, (GALT) 9 Mutations, Fetal |
| ARUP #: 0051270 |
| Methodology: Polymerase Chain Reaction/Single Nucleotide Extensions |
| Use: Evaluates 9 GALT gene mutations (Q188R, S135L, K285N, T138M, L195P, Y209C, IVS2-2 A>G, N314D and L218L) Clinical sensitivity approaches 80% in Caucasians; lower in other ethnic groups |
| Limitations: Only 9 common GALT mutations will be evaluated Only families with 2 GALT mutations included on this DNA panel should order this test |
| Follow-up: Cost-free result confirmation on neonatal cord blood post delivery is encouraged |
| Test name: Galactosemia (GALT) Sequencing |
| ARUP #: 0051346 |
| Methodology: Polymerase Chain Reaction/Sequencing |
| Use: Sequencing of the entire GALT gene coding region and intron/exon borders Clinical sensitivity for GALT sequencing is 98% |
| Limitations: Large GALT gene deletions or duplications will not be detected; analytical sensitivity may be compromised by rare primer site mutations |
| Follow-up: If 2 mutations are not detected in a known affected patient, GALT deletion/duplication analysis should be considered |
| Test name: Galactose-1-Phosphate in Red Blood Cells |
| ARUP #: 0081296 |
| Methodology: Gas Chromatography-Mass Spectrometry |
| Use: Monitor initial accumulation, response and compliance with dietary treatment for patients with an established diagnosis |
| Test name: CBC with Platelet Count & Automated Differential |
| ARUP #: 0040003 |
| Methodology: Automated Cell Count with Flow Cell Differential |
| Comments: Management (if symptomatic) |
| Test name: Hepatic Function Panel |
| ARUP #: 0020416 |
| Methodology: Refer to individual components. |
| Comments: Management (if symptomatic) |
| Test name: Prothrombin Time |
| ARUP #: 0030215 |
| Methodology: Electromagnetic Mechanical Clot Detection |
| Comments: Management (if symptomatic) |
| Test name: Electrolyte Panel |
| ARUP #: 0020410 |
| Methodology: Quantitative Ion-Selective Electrode/Enzymatic |
| Comments: Management (if symptomatic) |
| Test name: Ammonia, Plasma |
| ARUP #: 0020043 |
| Methodology: Colorimetry |
| Comments: Management (if symptomatic) |