Classic Galactosemia (GALT) Sequencing
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.
Manifestations of the disease 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 mental retardation. 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. Mutations in the GALT gene are responsible for the classic form of
galactosemia (G/G). This sequencing analysis can help identify the disease
causing mutations in patients. Single mutation analysis for carrier testing or
prenatal diagnosis is also available if the GALT mutations in the family are
known.
Specimen requirements: 5 to 10 ml of peripheral blood
collected in an EDTA (lavendar top) Vacutainer tube is preferred. The minimal
blood needed for reliable DNA isolation is 3 ml. If necessary, ACD solution A
Vacutainer tubes (yellow top) may be submitted. Please contact the laboratory
for more information.
Transport: Please contact Tim Wood or the molecular
diagnostic lab coordinator 1-800-473-9411 for shipping information. The specimen
should be kept at room temperature and delivered via overnight shipping. FedEx
is preferred. If shipment is delayed by one or two days, the specimen should be
refrigerated and shipped at room temperature. Do not freeze the specimen.
Samples collected on Friday can be safely designated for Monday delivery.
Analysis standards: Analysis will be complete within 4
weeks of sample receipt. The lab director assesses the quality and
interpretation of results. Technical staff members independently assess the
quality and interpretation of the test. The Greenwood Genetic Center Molecular
Diagnostic Laboratory is CLIA certified and actively participates in CAP
proficiency surveys.
Reporting of Test Results: Test results with
interpretation will be mailed and/or faxed following completion of the test.
Verbal reports will be telephoned to the person(s) requesting the test when an
abnormal test result occurs. Consultation with the laboratory director and
explanations of testing protocols will be supplied upon request.
Unknown mutation: CPT Codes: 83890, 83898(x4), 83904
(x3), 83909(x3), 83912
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