Biochemical and molecular studies of 132 patients with galactosemia

Ng, W.; Xu, Yan-Kang; Kaufman, Francine; Donnell, George N.; Wolff, Jon A.; Allen, Richard J.; Koritala, Sriveda; Reichardt, Juergen K.V.

doi:10.1007/bf00201593

Cited by 47 publications

(40 citation statements)

References 15 publications

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“…The Q188R mutation was selected for study because it accounts for 60-70% of the classic galactosemia alleles identified in Caucasian patients studied to date (26,27). Furthermore, it impacts a position only two codons from the presumed active site of the enzyme.…”

Section: Discussionmentioning

confidence: 99%

Heterodimer formation and activity in the human enzyme galactose-1-phosphate uridylyltransferase.

Elsevier

Wells

Quimby

et al. 1996

Proc. Natl. Acad. Sci. U.S.A.

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One of the fundamental questions concerning expression and function of dimeric enzymes involves the impact of naturally occurring mutations on subunit assembly and heterodimer activity. This question is of particular interest for the human enzyme galactose-1-phosphate uridylyltransferase (GALT), impairment of which results in the inherited metabolic disorder galactosemia, because many if not most patients studied to date are compound heterozygotes rather than true molecular homozygotes. Furthermore, the broad range of phenotypic severity observed in these patients raises the possibility that allelic combination, not just allelic constitution, may play some role in determining outcome. In the work described herein, we have selected two distinct naturally occurring null mutations of GALT, Q188R and R333W, and asked the questions (i) what are the impacts of these mutations on subunit assembly, and (ii) if heterodimers do form, are they active? To answer these questions, we have established a yeast system for the coexpression of epitopetagged alleles of human GALT and investigated both the extent of specific GALT subunit interactions and the activity of defined heterodimer pools. We have found that both homodimers and heterodimers do form involving each of the mutant subunits tested and that both heterodimer pools retain substantial enzymatic activity. These results are significant not only in terms of their implications for furthering our understanding of galactosemia and GALT holoenzyme structure-function relationships but also because the system described may serve as a model for similar studies of other complexes composed of multiple subunits.One of the fundamental questions raised by studies of the human enzyme galactose-1-phosphate uridylyltransferase (EC 2.7.7.12; GALT) concerns the role of subunit interaction on holoenzyme function and the impact of naturally occurring mutations on those interactions. Human GALT, impairment of which results in the potentially lethal disorder galactosemia, has been demonstrated to function as a dimer (1-7), ostensibly composed of identical subunits. However, the marked heterogeneity of naturally occurring point mutations identified in the GALT loci of galactosemia patients (e.g., ref. 8) indicates that many, if not most, of these patients are compound heterozygotes rather than true molecular homozygotes. The GALT enzymes expressed in these individuals, therefore, would be expected to consist of mixtures of homodimers and compound heterodimers, present in proportions reflective of the relative abundance, stability, and affinities of the individual subunits involved. This added level of heterogeneity may contribute to the broad range of phenotypic severity (for review, see ref. 9) observed for patients with galactosemia.

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Section: Discussionmentioning

confidence: 99%

Heterodimer formation and activity in the human enzyme galactose-1-phosphate uridylyltransferase.

Elsevier

Wells

Quimby

et al. 1996

Proc. Natl. Acad. Sci. U.S.A.

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“…10 p.Q188R also accounts for approximately 50 to 58% of the mutant alleles in Hispanics of Mexican ancestry. 29 The IVS2-2AϾG is rare but has been described in Hispanic populations and is …”

Section: ј-Cactgtctctcttctttctgtcaggggctcccacaggatcagaggctggggccaactmentioning

confidence: 99%

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

Jama

Nelson²,

Mao

et al. 2007

The Journal of Molecular Diagnostics

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Classic galactosemia is an autosomal recessive inherited error of galactose metabolism. It is caused by lack of galactose-1-phosphate uridyl transferase, an enzyme that is required to metabolize galactose-1-phosphate to uridine diphosphate galactose. The build up of galactose-1-phosphate is toxic at high levels and can damage the liver, brain, eyes, and other vital organs. Over 200 mutations have been identified in affected individuals. We describe an assay to identify nine target mutations or variants in the galactose-1-phosphate uridyl transferase gene, namely p.Q188R, p.S135L, p.K285N, p.L195P, p.T138M, p.Y209C, IVS2-2 A>G, p.L218L, and p.N314D. A single long-range PCR is followed by a multiplexed nucleotide extension assay (single nucleotide extension) and capillary electrophoresis to detect simultaneously all nine target mutations/variants. Fiftyfour previously characterized samples (47 clinical samples and seven controls) gave a 100% concordance. We also report a nontarget novel mutation, p.L192X, and its profile using single nucleotide extension. This assay can complement the enzyme activity assay and identify familial mutations for testing additional family members. (J Mol Diagn 2007, 9:618 -623;

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“…7,11,12 The incidence of transferase-deficient galactosaemia varies considerably between countries but has been estimated at 1 in 62 000 in a large human pan-ethnic study population. 13 Ireland is of particular interest in this context due to the existence within the population of an endogamous group, known as 'Travellers'.…”

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confidence: 99%

Genetic basis of transferase-deficient galactosaemia in Ireland and the population history of the Irish Travellers

et al. 1999

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Transferase-deficient galactosaemia, resulting from deficient activity of galactose-1-phosphate uridyltransferase (GALT), is relatively common among the Travellers, an endogamous group of commercial/industrial nomads within the Irish population. This study has estimated the incidence of classical transferase-deficient galactosaemia in Ireland and determined the underlying GALT mutation spectrum in the Irish population and in the Traveller group. Based upon a survey of newborn screening records, the incidence of classical transferase-deficient galactosaemia was estimated to be 1 in 480 and 1 in 30 000 among the Traveller and nonTraveller communities respectively. Fifty-six classical galactosaemic patients were screened for mutation in the GALT locus by standard molecular methods. Q188R was the sole mutant allele among the Travellers and the majority mutant allele among the non-Travellers (89.1%). Of the five non-Q188R mutant alleles in the non-Traveller group, one was R333G and one F194L with three remaining uncharacterised. Anonymous population screening has shown the Q188R carrier frequency to be 0.092 or 1 in 11 among the Travellers as compared with 0.009 or 1 in 107 among the non-Travellers. The Q188R mutation was shown to be in linkage disequilibrium with a Sac I RFLP flanking exon 6 of the GALT gene. This represents the first molecular genetic description of classical transferase-deficient galactosaemia in Ireland and raises intriguing questions concerning the genetic history of the Irish Travellers.

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Biochemical and molecular studies of 132 patients with galactosemia

Cited by 47 publications

References 15 publications

Heterodimer formation and activity in the human enzyme galactose-1-phosphate uridylyltransferase.

Heterodimer formation and activity in the human enzyme galactose-1-phosphate uridylyltransferase.

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

Genetic basis of transferase-deficient galactosaemia in Ireland and the population history of the Irish Travellers

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