Ellerine N P, Herring W J, Elsas L J, McKean M C, Klein P D, Danner D J
Department of Pediatrics, Emory University School of Medicine, Atlanta, Georgia 30322.
Biochem Med Metab Biol. 1993 Jun;49(3):363-74. doi: 10.1006/bmmb.1993.1037.
Maple syrup urine disease results from inherited defects in human nuclear genes for branched chain alpha-ketoacid dehydrogenase, a mitochondrial multienzyme complex. Thiamin pyrophosphate is necessary for complex activity and a thiamin-responsive form of maple syrup urine disease is known. Here we demonstrate the use of [1-13C]leucine oxidation to [13C]O2 quantified in breath samples as a means of assessing whole body leucine oxidation. Analysis of cultured cells from this patient shows the antigenic lack of the E2 subunit, yet she gained branched chain alpha-ketoacid dehydrogenase activity in response to diet supplementation with pharmacologic doses of thiamin. These cultured cells were used to seek a molecular basis for the observed thiamin response. Despite normal thiamin transport in these cells, medium supplementation of up to 1000 thiamin/liter failed to increase complex activity or cause the antigenic appearance of the missing protein. This lack of response in cultured cells suggests that the observed whole body response to thiamin must be a tissue-specific effect in liver, muscle, or kidney. In addition, allele-specific detection of paternal and maternal mutations was used to genotype family members in this pedigree.
枫糖尿症是由人类核基因中支链α-酮酸脱氢酶（一种线粒体多酶复合物）的遗传缺陷引起的。硫胺素焦磷酸对于该复合物的活性是必需的，并且已知一种硫胺素反应型的枫糖尿症。在此，我们展示了使用在呼吸样本中定量测定的[1-¹³C]亮氨酸氧化为[¹³C]O₂作为评估全身亮氨酸氧化的一种方法。对该患者培养细胞的分析显示E2亚基缺乏抗原性，但她在补充药理剂量的硫胺素饮食后获得了支链α-酮酸脱氢酶活性。这些培养细胞被用于寻找观察到的硫胺素反应的分子基础。尽管这些细胞中硫胺素转运正常，但在培养基中添加高达1000硫胺素/升未能增加复合物活性或导致缺失蛋白的抗原性出现。培养细胞中这种缺乏反应表明，观察到的全身对硫胺素的反应必定是肝脏、肌肉或肾脏中的组织特异性效应。此外，使用等位基因特异性检测父系和母系突变对该家系中的家庭成员进行基因分型。
