Mutations at the Galactose-1-P-Uridyltransferase Gene in Infants with a Positive Galactosemia Newborn Screening Test

Abstract

Newborn screening for galactosemia yields a high number of false-positive results. Confirmatory DNA testing for unknown galactosemia mutations on the initial positive sample using novel techniques of mutation detection tenders itself to reduce the recall rate. The potential benefits of confirmatory DNA testing, however, could be offset by the detection of a high percentage of galactosemia carriers, Duarte/galactosemia compound heterozygotes, and infants with benign sequence changes in the galactose-1-phosphate uridyltransferase (GALT) gene among infants with a positive biochemical screening test. Our aim was to determine the frequency and allelic distribution of all sequence changes in the GALT gene in 110 newborns with a positive total galactose screening test among 43,688 Austrian newborns screened consecutively. We found that only 20 of the 110 probands carried at least one known or novel candidate galactosemia mutation (one galactosemia homozygote, 7 Duarte/galactosemia compounds, 12 carriers) as judged by denaturing gradient gel electrophoresis and cleavage fragment length polymorphism analysis. Four novel galactosemia candidate mutations (Q9H, A46fsdelCAGCT, M129T, L342I) were identified. Sixty-seven probands had no detectable sequence changes and 23 carried only the benign Duarte or Los Angeles variant alleles or silent mutations. We conclude that a rapid and automatable confirmation test for unknown GALT mutations, e.g. on a high-density oligonucleotide array basis, has the potential to lower the recall rate of galactosemia screening in our population by about five-fold from 0.25 to 0.046%. Further research, however, will be required before the development of such a test can be advocated. Classical galactosemia (McKusick 230400) is an autosomal recessive inborn error of carbohydrate metabolism caused by a deficiency of GALT occurring with an incidence of 1:40,000 -60,000 in Caucasian populations (1). Newborn screening and dietary galactose restriction prevent the life-threatening neonatal symptoms of galactosemia. Despite dietary treatment, the majority of affected children develop long-term complications including mental retardation, speech deficits, and ovarian failure.Galactosemia screening by microbiological or biochemical tests for elevated blood galactose/galactose-1-P and/or reduced GALT activity yields a high rate of false positives (2). Only 1 in about 190 infants recalled in galactosemia screening programs across the United States will actually have galactosemia (3). Because of the potentially rapid and fatal course of the disease, newborns with positive test results have to be recalled urgently. This causes substantial anxiety among the families concerned (4) and increases the workload of the screening centers.DNA confirmatory testing for common mutations on the original dried blood spot with a positive initial biochemical screening result has been used to reduce the number of false positives in screening programs for cystic fibrosis (5) and hemoglobinopathies (6). Although two common mutation...

Early and severe indirect hyperbilirubinemia as a manifestation of galactosemia

“…8 The estimated incidence in the United States is approximately 1 in 40 000 to 60 000. 9 Classic galactosemia manifests in neonates with vomiting, diarrhea, jaundice, hepatomegaly, ascites and/or Escherichia coli sepsis within a few days after starting milk ingestion.…”

Simultaneous Amplification, Detection, and Analysis of Common Mutations in the Galactose-1-Phosphate Uridyl Transferase Gene

“…3,5,15,16 Abnormal screening tests are followed by confirmatory testing using enzymatic activity. 17 The GALT enzyme is unstable, and the assay for enzyme activity is best performed on fresh heparin anticoagulated blood. DNA analysis for common mutations can be used in conjunction with enzyme activity to confirm familial mutations.…”

Classic Galactosemia Presenting with Unilateral Peters’ Anomaly

“…In addition, this patient carried a Q188R mutation, which accounts for 60% of galactosemia alleles in the Caucasian population. This is considered a severe mutation and results in a lack of galactose-1-phosphate uridyltransferase activity [2] .…”