Shimizu Makiko, Allerston Charles K, Shephard Elizabeth A, Yamazaki Hiroshi, Phillips Ian R
Laboratory of Drug Metabolism and Pharmacokinetics, Showa Pharmaceutical University, Machida, Tokyo, 194-8543, Japan.
Br J Clin Pharmacol. 2014 May;77(5):839-51. doi: 10.1111/bcp.12240.
The aim of this study was to investigate relationships between flavin-containing mono-oxygenase 3 (FMO3) genotype and phenotype (conversion of odorous trimethylamine into non-odorous trimethylamine N-oxide) in a large Japanese cohort suffering from trimethylaminuria.
Urinary excretion of trimethylamine and trimethylamine N-oxide was determined for 102 volunteers with self-reporting symptoms of trimethylaminuria. For each we determined the sequence of the entire coding region, plus 1.3 kb of flanking intronic and 2.5 kb of the upstream region of the FMO3 gene. The affect of upstream variants on transcription was determined with a reporter gene assay.
Seventy-eight subjects were diagnosed as suffering from trimethylaminuria, based on urinary excretion of <90% of total TMA as TMA N-oxide. Of these, 13 were classified as severe, 56 as moderate and nine as mild cases, excreting <43%, 48-70% and 73-83% of trimethylamine as trimethylamine N-oxide, respectively. Twenty-seven mutations were identified in FMO3, 15 in the coding region, of which eight abolish or severely impair FMO3 activity (Pro70Leu, Cys197fsX, Thr201Lys, Arg205Cys, Met260Val, Trp388Ter, Gln470Ter and Arg500Ter), and 12 in the upstream region. The mutations segregate into 19 haplotypes, including four different combinations of upstream mutations, each of which reduces transcriptional activity in comparison with the ancestral upstream sequence of FMO3.
Comparisons of genotype and phenotype reveal that severe trimethylaminuria is caused by loss of function mutations in FMO3. For moderate and mild cases the situation is more complex, with most resulting from factors other than FMO3 genotype. Our results have implications for the diagnosis and management of the disorder.
本研究旨在调查在大量患有三甲胺尿症的日本人群队列中，含黄素单加氧酶3（FMO3）基因型与表型（将有气味的三甲胺转化为无气味的氧化三甲胺）之间的关系。
对102名自述有三甲胺尿症症状的志愿者测定了三甲胺和氧化三甲胺的尿排泄量。对每个人，我们测定了FMO3基因整个编码区的序列，外加1.3kb的侧翼内含子序列和2.5kb的上游区域序列。通过报告基因测定法确定上游变异对转录的影响。
基于尿中氧化三甲胺占总三甲胺的比例<90%，78名受试者被诊断为患有三甲胺尿症。其中，13例被分类为重度，56例为中度，9例为轻度，分别将<43%、48 - 70%和73 - 83%的三甲胺转化为氧化三甲胺。在FMO3中鉴定出27个突变，其中15个在编码区，8个使FMO3活性丧失或严重受损（Pro70Leu、Cys197fsX、Thr201Lys、Arg205Cys、Met260Val、Trp388Ter、Gln470Ter和Arg500Ter），12个在上游区域。这些突变分为19种单倍型，包括四种不同的上游突变组合，与FMO3的祖先上游序列相比，每种组合均降低转录活性。
基因型与表型的比较表明，重度三甲胺尿症是由FMO3功能丧失突变引起的。对于中度和轻度病例，情况更为复杂，大多数是由FMO3基因型以外的因素导致的。我们的结果对该疾病的诊断和管理具有重要意义。
