RESUMO
A stable isotope dilution assay using D3-mevalonic acid was developed and applied to the study of mevalonic aciduria. The method also appears to be suitable for the evaluation of different therapeutic regimens in patients with hypercholesterolemia. Mevalonic acid was isolated by liquid partition chromatography and quantified as the underivatized lactone by means of ammonia chemical ionization selected ion monitoring capillary gas chromatography-mass spectrometry. In heterozygotes there was significantly greater urinary excretion of mevalonic acid, while the range of enzymatic activity of mevalonate kinase showed an overlap with that of controls. The analysis of amniotic fluids of two pregnancies at risk for mevalonic aciduria showed a 3277-fold elevation as compared to controls in the first case, diagnostic of an affected fetus, and a normal value in the second one. Mevalonic acid concentration was much increased in tissues of the affected and aborted fetus. Concentrations ranged from 840 to 1120 mumol/kg in various tissues and were as high as 1810 mumol/kg in brain. Concentrations in control fetal tissues were approximately 1 mumol/kg.
Assuntos
Doenças Fetais/diagnóstico , Heterozigoto , Ácido Mevalônico/urina , Fosfotransferases (Aceptor do Grupo Álcool) , Diagnóstico Pré-Natal , Adulto , Líquido Amniótico/química , Linhagem Celular , Criança , Colesterol/biossíntese , Feminino , Feto/química , Cromatografia Gasosa-Espectrometria de Massas/métodos , Humanos , Técnicas de Diluição do Indicador , Lactente , Recém-Nascido , Masculino , Ácido Mevalônico/análise , Ácido Mevalônico/sangue , Ácido Mevalônico/metabolismo , Fosfotransferases/metabolismo , Gravidez , Sensibilidade e EspecificidadeRESUMO
Mevalonic aciduria due to mevalonate kinase deficiency, an inherited defect of cholesterol biosynthesis, has presented with clinical variability in 10 patients from 7 families. We sought to define a genetic basis for this heterogeneity by determining mevalonate kinase activity in fibroblast heterokaryons obtained by polyethylene glycol fusion. To this end we developed a DEAE-cellulose (Cl-) column chromatography procedure for assessing mevalonate kinase in cell extracts that would allow multiple rapid analyses. Fusion of control fibroblasts with those from affected patients from six families with mevalonate kinase deficiency yielded 37% of the mean control activity. None of the fusions between the six cell lines of patients resulted in measurable mevalonate kinase activity. Using the chromatographic procedure, we developed an optimized assay for mevalonate kinase in biopsied chorionic villi. Km values for chorionic villi were similar to those obtained in fibroblasts. Mevalonate kinase activity in biopsied chorionic villi showed a linear increase (0.75-4.3 nmol/min per mg protein) with gestational age from 7 to 14 weeks. Using the optimized assay in biopsied chorionic villi we performed a first-trimester prenatal diagnosis in a pregnancy at risk for mevalonate kinase deficiency and correctly diagnosed an unaffected fetus. The availability of an optimized assay for mevalonate kinase in biopsied chorionic villi should allow reliable first-trimester prenatal diagnosis for families at risk.