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S Chaing

Publications and source records attributed to S Chaing.

4 recordsLinked to original sources
PubMed2003

Evaluation of 3-methylcrotonyl-CoA carboxylase deficiency detected by tandem mass spectrometry newborn screening.

Since the addition of tandem mass spectrometry (MS/MS) to the North Carolina Newborn Screening Program, 20 infants with two consecutive elevated 3-hydroxyisovalerylcarnitine (C5OH) levels have been evaluated for evidence of inborn errors of metabolism associated with this metabolite. Ten of these 20 infants had significant concentrations of both 3-hydroxyisovaleric acid and 3-methylcrotonylglycine in their urine, suggestive of 3-methylcrotonyl-CoA carboxylase (3-MCC) deficiency. Four of these 10 were infants whose abnormal metabolites were found to be of maternal origin. Of 8 patients with probable 3-MCC deficiency, 7 have been tested and found to have the enzyme deficiency confirmed in lymphoblasts or cultured fibroblasts; one of these 7 infants had only marginally decreased 3-MCC activity in lymphocytes but deficient 3-MCC in fibroblasts. We estimate the incidence of 3-MCC deficiency at 1:64000 live births in North Carolina. We conclude that MS/MS newborn screening will detect additional inborn errors of metabolism, such as 3-MCC deficiency, not traditionally associated with newborn screening. The evaluation of newborns with two abnormally elevated C5OH levels on MS/MS newborn screening should include, at least, urine organic acid analysis by capillary GC-MS and a plasma acylcarnitine profile by MS/MS. Long-term follow-up is needed to determine the outcome of presymptomatically diagnosed patients with 3-MCC deficiency by MS/MS newborn screening.

Acids↗
PubMed1996

Activation of a recombinant human factor VII structural analogue alters its affinity of binding to tissue factor.

A competitive enzyme-linked immunoadsorbent assay (ELISA) technique has been developed to facilitate quantitative analysis of the earliest step in the initiation of the extrinsic pathway of coagulation, i.e., complex formation of factor VII/VIIa with tissue factor. The ELISA measures the binding of biotinylated human plasma factor VII to relipidated recombinant human tissue factor. Quantitation of the relative affinity (expressed as IC50) of any factor VII molecular population or structural analogue for tissue factor can be determined by competitive binding. Subnanomolar concentrations of both wild-type recombinant human factor VII (rFVII) and rFVII(R152Q), a mutation at the FVII activation site, competed effectively with biotinylated plasma-derived factor VII in binding to tissue factor. In contrast, the affinity of rFVII(R79Q), a mutation in the first epidermal growth factor-like domain, was 12-fold lower. Following activation of rFVII(R79Q), its affinity for tissue factor and enzymatic activity increased 4-fold and 6-fold, respectively. For wild-type rFVII, enzymatic activity rose significantly following activation. However, its affinity for tissue factor was unchanged. We conclude that both the activation state of factor VII and the mutation of amino-acid residues within the first epidermal growth factor-like domain may alter the affinity of factor VII for tissue factor.

Binding Sites↗
PubMed1994

Severe factor VII deficiency caused by mutations abolishing the cleavage site for activation and altering binding to tissue factor.

Factor VII (F.VII) is a vitamin-K-dependent serine protease required in the early stages of blood coagulation. We describe here a patient with severe F.VII deficiency, with a normal plasma F.VII antigen level (452 ng/mL) and F.VII activity less than 1%, who is homozygous for two defects: a G-->A transition at nucleotide 6055 in exon 4, which results in an Arg-->Gln change at amino acid 79 (R79Q); and a G-->A transition at nucleotide 8961 in exon 6, which results in an Arg-->Gln substitution at amino acid 152 (R152Q). The R79Q mutation occurs in the first epidermal growth factor (EGF)-like domain, which has previously been implicated in binding to tissue factor. The R152Q mutation occurs at a site (Arg 152-Ile 153) that is normally cleaved to generate activated F.VII (F.VIIa). Analysis of purified F.VII from patient plasma shows that the material cannot be activated by F.Xa and cofactors. In addition, in an in vitro binding assay using relipidated recombinant tissue factor, patient plasma showed markedly reduced binding to tissue factor at all concentrations tested. In an effort to separate the contributions of the two mutations, three recombinant variants, wild-type, R79Q, and R152Q, were prepared and analyzed. The R152Q variant had markedly reduced activity in a clotting assay, whereas R79Q showed a milder, concentration-dependent reduction. The R152Q variant exhibited nearly normal binding in the tissue factor binding assay, whereas the R79Q variant had markedly reduced binding. The time course of activation of the R79Q variant was slowed compared with wild-type. Our results suggest that the first EGF-like domain is required for binding to tissue factor and that the F.VII zymogen lacks activity and requires activation for expression of biologic activity.

Adult↗