Molecular genetics of citrin deficiency and search for the factor(s) and mechanism of adult-onset type II citrullinemia onset

Citrin缺乏症是一种新发现的疾病，包括胆汁淤积性新生儿肝炎(NICCD)和成人-II型瓜氨酸血症(CTLN2)，是编码Citrin的SLC25A13基因突变的结果。Citrin缺乏会在生命的头几个月导致NICCD，在大多数情况下，症状通常在第一年就会自行解决。在经历了一段从一到几十年的表面上健康的时期后，一些Citrin缺乏的患者继续发展为严重的CTLN2。从Citrin作为肝型天冬氨酸-谷氨酸载体定位于线粒体内膜的功能来看，NICCD和CTLN2的一些不同症状可能是通过天冬氨酸从线粒体输出到胞浆和苹果酸-天冬氨酸NADH穿梭的缺陷来理解的。在本研究中，我们鉴定了近20个新的SLC25A13突变，并建立了它们的DNA诊断。更进一步的…此外，我们还建立了一种新的诊断方法，利用Western印迹分析检测淋巴细胞中的Citrin蛋白。我们不仅在日本发现了Citrin缺乏症患者，而且在其他国家也发现了Citrin缺乏患者。到目前为止，我们已经诊断出NICCD(203名日本人，40名中国人，6名韩国人，4名越南人，3名高加索人，3名巴勒斯坦人，2名犹太人，2名以色列人，1名巴基斯坦人)和CTLN患者(157名日本人，3名中国人和2名韩国人)。DNA诊断显示，日本人群的携带者频率为1，65(纯合子频率：1/17,000)。我们的人群分析在日本患者中发现了12个已知突变，在东亚发现了许多携带者：韩国和中国的携带者比例分别为1/112和1/65(广东和湖南：1/40，香港：1/48，台湾：1/57)，这表明超过100,000名东亚人是Citrin缺乏症的纯合子。另一方面，我们培育了Citrin-KO(基因敲除)小鼠，但这些小鼠没有表现出人类Citrin缺乏症的特征。基于与人类相比，小鼠肝脏中甘油磷酸穿梭活性的增强可以弥补Citrin功能的丧失的假设，我们产生了Citrin基因和线粒体3-磷酸甘油脱氢酶(MGPDH)基因联合破坏的小鼠。由此产生的双KO小鼠表现出瓜氨酸血症、高氨血症，口服蔗糖进一步增加，低血糖和脂肪肝；所有这些特征都是人类Citrin缺乏症的(提交给J Biol Chem)。较少

Citrin deficiency is a newly-established disease entity that encompasses both cholestatic neonatal hepatitis (NICCD) and adult-onse: type II citrullinemia (CTLN2), and results from mutations in the SLC25A13 gene that encodes citrin. Citrin deficiency results in NICCD during the first few months of life, with symptoms usually self-resolving by the first year in most cases. Following an apparently healthy period that can last from one to several decades, some patients with citrin deficiency go on to develop severe CTLN2. From the function of citrin as a liver-type aspartate-glutamate carrier localized in the mitochondrial inner membrane, some of the various symptoms of NICCD and CTLN2 may be understood through the defects of aspartate export from mitochondria to cytosol and of malate-aspartate NADH shuttle. It is, however, still difficult to clarify the mechanism of CTLN2-onset.In the present study, we identified near 20 novel SLC25A13 mutations and established their DNA diagnoses. Furth … More ermore, we also developed a novel diagnostic method to detect citrin protein in lymphocytes by using Western blot analysis. We have found the patients with citrin deficiency not only in Japan but also in other country. So far, we have diagnosed NICCD (203 Japanese, 40 Chinese, 6 Korean, 4 Vietnamese, 3 Caucasian, 3 Palestinian, 2 Jewish, 2 Israeli, 1 Pakistani) and CTLN2 (157 Japanese, 3 Chinese and 2 Korean) patients. DNA diagnosis revealed that the carrier frequency is 1,65 (homozygote frequency: 1/17,000) in the Japanese population. Our population analysis of 12 known mutations identified in Japanese patients detected many carriers in East Asia: the rates are 1/112 in Korea and 1/65 in China (Guangdong and Hunan: 1/40, Hong Kong: 1/48, Taiwan: 1/57), suggesting that over 100,000 East Asians are homozygotes of citrin deficiency. On the other hand, we generated citrin-KO (knockout) mice, but the mice failed to display features of human citrin deficiency. Based on the hypothesis that an enhanced glycerol phosphate shuttle activity in mouse liver compared to that in human can compensate for the loss of citrin function, we generated mice with a combined disruption of the genes for citrin and mitochondrial glycerol 3-phosphate dehydrogenase (mGPDH). The resulting double-KO mice demonstrated citrullinemia, hyperammonemia that was further elevated by oral sucrose administration, hypoglycemia, and fatty liver; all features of human citrin deficiency (submitted to J Biol Chem). Less