Purpose: We previously reported a deletion of the Galactose-1-Phosphate Uridyl Transferase (GALT) gene. This deletion can cause apparent homozygosity for variants located on the opposite allele, potentially resulting in a discrepancy between the biochemical phenotype and the apparent genotype in an individual. The purpose of this study was to determine the deletion breakpoints, allowing the development of a rapid and reliable molecular test for the mutation. Methods: A Polymerase Chain Reaction walking strategy was used to map the 5= and 3= breakpoints. The junction fragment was amplified and sequenced to precisely characterize the deletion breakpoints. Results: The deletion has a bipartite structure involving two large segments of the GALT gene, while Classic galactosemia refers to severe galactose-1-phosphate uridyltransferase (GALT) deficiency and manifests within the first week of life with poor feeding, jaundice, vomiting, liver dysfunction, increased bleeding tendency and septicemia, leading to death if left untreated. 1 The disease can be easily managed by lactose restriction, although some long term complications may not be prevented. Diagnostic work-up for classic galactosemia is often initiated following abnormal newborn screening. Classic galactosemia can be confirmed by extremely low or absent GALT enzymatic activity in the hemolysates; while variant forms or carrier status may require confirmation by further biochemical analysis and/or molecular genotyping of the GALT gene. Our laboratory performs both biochemical phenotyping and molecular genotyping to confirm the diagnosis of galactosemia.The biochemical analysis consists of assessment of GALT enzyme activity, measurement of galactose-1-phosphate (Gal-1-P; the GALT enzyme substrate) and GALT protein isozyme analysis in red cells. The first tier of molecular analysis consists of genotyping for 9 common GALT variants (Q188R, N314D, L218L, S135L, K285N, L195P, T138M, Y209C, and IVS2-2AϾG). These mutations account for the vast majority of galactosemia alleles in various populations. 2 The second tier of testing consists of GALT gene sequencing (the exons and the intron/exon junctions) that will detect less common coding and splice junction mutations. These combined biochemical and molecular approaches provide a comprehensive characterization of the patient's biochemical phenotype and genotype to guide nutritional management and genetic counseling.Our combined approach also enables identification of variants that may otherwise go undetected or lead to erroneous diagnosis. For example, the discrepancy between biochemical phenotype and molecular genotype due to the presence of a deletion on one of the alleles results in apparent homozygosity for the variant on the opposite allele. Previously, a large deletion of about 5 kb in the GALT gene was identified because it resulted in discordance between biochemical phenotype and the apparent genotype. 3,4 We have encountered this mutation numerous times during our testing for galactosemia. Here we describe the ...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.