Pinotti M, Toso R, Redaelli R, Berrettini M, Marchetti G, Bernardi F
Dipartimento di Biochimica e Biologia Molecolare - CIBF, Sezione SBPGU, Università di Ferrara, Ferrara; the Divisione di Ematologia, Ospedale Niguarda, Milano, Italy.
Blood. 1998 Sep 1;92(5):1646-51.
In three Italian patients, two point mutations and a short deletion were found in the intron 7 of factor VII gene, clustered in the donor splice site and located in the first of several repeats. The mutation 9726+5G-->A, the most frequent cause of symptomatic factor VII deficiency in Italy, as well as the deletion (9729del4) gave rise in expression studies to abnormally spliced transcripts, which were exclusively produced from the cryptic site in the second repeat. The insertion in the mature mRNA of the first intronic repeat caused (9726+5G-->A) a reading frameshift, abolishing most of the factor VII catalytic domain, or produced (9729del4), an altered factor with 11 additional residues, the activity of which was not detectable in the cell medium after mutagenesis and expression studies. Studies of factor VII ectopic mRNA from leukocytes and expression studies indicated that the deleted gene produced 30% of normally spliced transcript. Differently, the 9726+5G-->A mutation permitted a very low level (0.2% to 1%) of correct splicing to occur, which could be of great importance to prevent the onset, in the homozygous patients, of most of the life-threatening bleeding symptoms. The 9726+7A-->G mutation was found to be a rare and functionally silent polymorphism. These findings, which provide further evidence of the interplay of sequence and position in the 5' splice site selection, throw light on the heterogeneous molecular bases and clinical phenotypes of FVII deficiency.
在三名意大利患者中，在凝血因子VII基因的第7内含子中发现了两个点突变和一个短缺失，它们聚集在供体剪接位点，位于几个重复序列中的第一个。突变9726 +5G→A是意大利有症状的凝血因子VII缺乏症最常见的病因，与缺失（9729del4）一样，在表达研究中导致异常剪接的转录本，这些转录本仅从第二个重复序列中的隐蔽位点产生。第一个内含子重复序列插入成熟mRNA中导致（9726 +5G→A）读码框移位，消除了大部分凝血因子VII催化结构域，或者产生了（9729del4），一种带有11个额外残基的改变因子，在诱变和表达研究后，其活性在细胞培养基中无法检测到。对白细胞中凝血因子VII异位mRNA的研究和表达研究表明，缺失的基因产生了30%正常剪接的转录本。不同的是，9726 +5G→A突变允许极低水平（0.2%至1%）的正确剪接发生，这对于防止纯合患者出现大多数危及生命的出血症状可能非常重要。9726 +7A→G突变被发现是一种罕见的、功能上沉默的多态性。这些发现为5'剪接位点选择中序列和位置的相互作用提供了进一步的证据，揭示了凝血因子VII缺乏症的异质分子基础和临床表型。
