Fujioka H, Okano Y, Inada H, Asada M, Kawamura T, Hase Y, Yamano T
Department of Pediatrics, Osaka City University Graduate School of Medicine, Osaka, Japan.
Eur J Hum Genet. 2001 Dec;9(12):931-7. doi: 10.1038/sj.ejhg.5200749.
Congenital hyperinsulinism and hyperammonaemia (CHH) is caused by dysregulation of glutamate dehydrogenase (GDH). We characterised the GDH gene in two Japanese patients with CHH. Patient 1 showed late-onset and mild hypoglycaemic episodes and mild hyperammonaemia, compared with patient 2. In GDH activity of lymphoblasts, patient 1 showed twofold higher basal GDH activity than control subjects and mild insensitivity for GTP inhibition. Patient 2 showed severe insensitivity for GTP inhibition, and similar allosteric stimulation by ADP in the controls. Genetic studies identified heterozygous and de novo L413V and G446D mutations in patients 1 and 2, respectively. COS cell expression study confirmed that both mutations were disease-causing gene. The insensitivity for GTP inhibition in L413V and G446D was emphasised in COS cell expression system as a result of the dosage effect of mutant GDH gene. L413V showed less impairment of GDH than G446D based on biochemical and genetic results, which was consistent with the clinical phenotype. Based on the structure of bovine GDH, G446D was located in GTP binding site of pivot helix and its surroundings, while L413V was located in alpha-helix of antenna-like structure. These different locations of mutations gave different effects on GDH enzyme. The antenna-like structure plays an important role in GDH activity.
先天性高胰岛素血症和高氨血症（CHH）由谷氨酸脱氢酶（GDH）调节异常引起。我们对两名患有CHH的日本患者的GDH基因进行了特征分析。与患者2相比，患者1表现出迟发性和轻度低血糖发作以及轻度高氨血症。在淋巴母细胞的GDH活性方面，患者1的基础GDH活性比对照受试者高两倍，并且对GTP抑制具有轻度不敏感性。患者2对GTP抑制表现出严重不敏感性，且在对照中对ADP有类似的变构刺激作用。基因研究分别在患者1和患者2中鉴定出杂合和新生的L413V和G446D突变。COS细胞表达研究证实这两种突变都是致病基因。由于突变型GDH基因的剂量效应，在COS细胞表达系统中L413V和G446D对GTP抑制的不敏感性得到了强调。基于生化和基因结果，L413V对GDH的损害比G446D小，这与临床表型一致。基于牛GDH的结构，G446D位于枢轴螺旋的GTP结合位点及其周围，而L413V位于天线样结构的α螺旋中。这些突变的不同位置对GDH酶产生了不同的影响。天线样结构在GDH活性中起重要作用。
