Characterization of two missense variants in the hydroxymethylbilane synthase gene in the Israeli population, which differ in their associations with acute intermittent porphyria

Schneider‐Yin, Xiaoye; Ulbrichová, Dana; Mamet, Rivka; Martásek, Pavel; Marohnic, Christopher C.; Goren, Avner; Minder, Elisabeth I.; Schoenfeld, Nili

doi:10.1016/j.ymgme.2008.03.001

Cited by 10 publications

(6 citation statements)

References 19 publications

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“…For wt HMBS the T m obtained was very high, i.e. T m ~74°C (Table 4), as expected from the high thermal stability of the enzyme activity [14,15,45]. R116W and R173W displayed lower T m -values, approx.…”

Section: Resultssupporting

confidence: 57%

Conformational stability and activity analysis of two hydroxymethylbilane synthase mutants, K132N and V215E, with different phenotypic association with acute intermittent porphyria

et al. 2013

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The autosomal dominantly inherited disease AIP (acute intermittent porphyria) is caused by mutations in HMBS [hydroxymethylbilane synthase; also known as PBG (porphobilinogen) deaminase], the third enzyme in the haem biosynthesis pathway. Enzyme-intermediates with increasing number of PBG molecules are formed during the catalysis of HMBS. In this work, we studied the two uncharacterized mutants K132N and V215E comparative with wt (wild-type) HMBS and to the previously reported AIP-associated mutants R116W, R167W and R173W. These mainly present defects in conformational stability (R116W), enzyme kinetics (R167W) or both (R173W). A combination of native PAGE, CD, DSF (differential scanning fluorimetry) and ion-exchange chromatography was used to study conformational stability and activity of the recombinant enzymes. We also investigated the distribution of intermediates corresponding to specific elongation stages. It is well known that the thermostability of HMBS increases when the DPM (dipyrromethane) cofactor binds to the apoenzyme and the holoenzyme is formed. Interestingly, a decrease in thermal stability was measured concomitant to elongation of the pyrrole chain, indicating a loosening of the structure prior to product release. No conformational or kinetic defect was observed for the K132N mutant, whereas V215E presented lower conformational stability and probably a perturbed elongation process. This is in accordance with the high association of V215E with AIP. Our results contribute to interpret the molecular mechanisms for dysfunction of HMBS mutants and to establish genotype–phenotype relations for AIP.

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Section: Resultssupporting

confidence: 57%

Conformational stability and activity analysis of two hydroxymethylbilane synthase mutants, K132N and V215E, with different phenotypic association with acute intermittent porphyria

et al. 2013

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“…However, only six of these had <3% of WT expressed activity or reduced thermostability. Review of the original reports for the other six variants identified 13 reportedly symptomatic AIP patients who had variants encoding p.T59I [Schneider‐Yin et al., ], p.E86V [Floderus et al., ], p.R225Q [Floderus et al., ; von Brasch et al., ], or p.R321H [Schuurmans et al., ; von Brasch et al., ; Anyaegbu et al., ; Cerbino et al., ]. However, the pathogenicity of most of these patients was not verified by elevated urinary ALA or PBG levels with the exception of (1) three patients with p.R321H who also had a second and pathogenic HMBS mutation [von Brasch et al., ; Cerbino et al., ]; and (2) one patient with p.R321H who had significantly increased urinary ALA or PBG concentrations, suggesting the presence of an unidentified second and pathogenic mutation [Anyaegbu et al., ] (Supp.…”

Section: Discussionmentioning

confidence: 99%

Acute Intermittent Porphyria: Predicted Pathogenicity ofHMBSVariants Indicates Extremely Low Penetrance of the Autosomal Dominant Disease

et al. 2016

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Acute Intermittent Porphyria results from hydroxymethylbilane synthase (HMBS) mutations that markedly decrease HMBS enzymatic activity. This dominant disease is diagnosed when heterozygotes have life-threatening acute attacks, while most heterozygotes remain asymptomatic and undiagnosed. Although >400 HMBS mutations have been reported, the prevalence of pathogenic HMBS mutations in genomic/exomic databases, and the actual disease penetrance are unknown. Thus, we interrogated genomic/exomic databases, identified non-synonymous variants (NSVs) and consensus splice-site variants (CSSVs) in various demographic/racial groups, and determined the NSV’s pathogenicity by prediction algorithms and in vitro expression assays. Caucasians had the most: 58 NSVs and two CSSVs among ~92,000 alleles, a 0.00575 combined allele frequency. In silico algorithms predicted 14/58 NSVs as “likely-pathogenic”. In vitro expression identified 10/58 NSVs as likely-pathogenic (seven predicted in silico), which together with two CSSVs had a combined allele frequency of 0.00056. Notably, six presumably pathogenic mutations/NSVs in the Human Gene Mutation Database were benign. Compared to the recent prevalence estimate of symptomatic European heterozygotes (~0.000005), the prevalence of likely-pathogenic HMBS mutations among Caucasians was >100 times more frequent. Thus, the estimated penetrance of acute attacks was ~1% of heterozygotes with likely-pathogenic mutations, highlighting the importance of predisposing/protective genes and environmental modifiers that precipitate/prevent the attacks.

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“…Identification of disease-specific mutations in the corresponding genes (HMBS, 4 CPOX, and PPOX, respectively) is important for detection and counseling of asymptomatic relatives in families with acute porphyria (1 ). Of the at least 510 mutations that have been identified in these genes (www.hgmd.cf.ac.uk) (3)(4)(5)(6)(7)(8), most are restricted to one or a few families (9,10 ).…”

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confidence: 99%

Diagnostic Strategies for Autosomal Dominant Acute Porphyrias: Retrospective Analysis of 467 Unrelated Patients Referred for Mutational Analysis of the HMBS, CPOX, or PPOX Gene

et al. 2009

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Background: Clinically indistinguishable attacks of acute porphyria occur in acute intermittent porphyria (AIP), hereditary coproporphyria (HCP), and variegate porphyria (VP). There are few evidence-based diagnostic strategies for these disorders. Methods: The diagnostic sensitivity of mutation detection was determined by sequencing and gene-dosage analysis to search for mutations in 467 sequentially referred, unrelated patients. The diagnostic accuracy of plasma fluorescence scanning, fecal porphyrin analysis, and porphobilinogen deaminase (PBGD) assay was assessed in mutation-positive patients (AIP, 260 patients; VP, 152 patients; HCP, 31 patients). Results: Sensitivities (95% CI) for mutation detection were as follows: AIP, 98.1% (95.6%–99.2%); HCP, 96.9% (84.3%–99.5%); VP, 100% (95.7%–100%). We identified 5 large deletions in the HMBS gene (hydroxymethylbilane synthase) and one in the CPOX gene (coproporphyrinogen oxidase). The plasma fluorescence scan was positive more often in VP (99% of patients) than in AIP (68%) or HCP (29%). The wavelength of the fluorescence emission peak and the fecal coproporphyrin isomer ratio had high diagnostic specificity and sensitivity for differentiating between AIP, HCP, and VP. DNA analysis followed by PBGD assay in mutation-negative patients had greater diagnostic accuracy for AIP than either test alone. Conclusions: When PBG excretion is increased, 2 investigations (plasma fluorescence scanning, the coproporphyrin isomer ratio) are sufficient, with rare exceptions, to identify the type of acute porphyria. When the results of PBG, 5-aminolevulinate, and porphyrin analyses are within reference intervals and clinical suspicion that a past illness was caused by an acute porphyria remains high, mutation analysis of the HMBS gene followed by PBGD assay is an effective strategy for diagnosis or exclusion of AIP. .

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Characterization of two missense variants in the hydroxymethylbilane synthase gene in the Israeli population, which differ in their associations with acute intermittent porphyria

Cited by 10 publications

References 19 publications

Conformational stability and activity analysis of two hydroxymethylbilane synthase mutants, K132N and V215E, with different phenotypic association with acute intermittent porphyria

Conformational stability and activity analysis of two hydroxymethylbilane synthase mutants, K132N and V215E, with different phenotypic association with acute intermittent porphyria

Acute Intermittent Porphyria: Predicted Pathogenicity ofHMBSVariants Indicates Extremely Low Penetrance of the Autosomal Dominant Disease

Diagnostic Strategies for Autosomal Dominant Acute Porphyrias: Retrospective Analysis of 467 Unrelated Patients Referred for Mutational Analysis of the HMBS, CPOX, or PPOX Gene

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