Matsuo Yoko, Mizuochi Tatsuki, Miho Mitsuo, Nakagawa Shinichiro, Ozono Shuichi, Ueda Koichiro, Sogabe Yoko, Seki Ritsuko, Soejima Kenji, Okamura Takashi, Yamashita Yushiro
Department of Pediatrics and Child Health, Kurume University School of Medicine.
Division of Hematology and Oncology, Department of Medicine, Kurume University School of Medicine.
Kurume Med J. 2017 Apr 13;63(1.2):23-28. doi: 10.2739/kurumemedj.MS6300007. Epub 2017 Mar 15.
A 10-day-old male patient was referred to our hospital with severe umbilical bleeding. Prothrombin time (PT) and activated partial thromboplastin time (APTT) were prominently prolonged. Plasma coagulation factor X (FX) activity and antigen levels were 1% and 0.6%, respectively. A DNA sequence analysis of his leukocytes revealed a compound heterozygous state; known Gly244 to Arg (p.G244R) in exon 6 and a novel mutation of Gly 435 to Ser (p.G435S) in exon 8. A pedigree analysis showed that p.G244R originated from the paternal side, while p.G435S was from the maternal side. A p.G244R mutation was reported previously as FX and this mutated protein was synthesized as a non-secretable protein. The glycine at amino acid position 435 in the C-terminal region is completely conserved in the trypsin-like serine protease family, including thrombin, FVII, protein C, plasmin, trypsin, and chymotrypsin. In a three-dimensional structural model of FX, Gly 435 was located within the 11 β-strand and buried in the back of the catalytic pocket. Therefore, the substitution to serine was expected to disrupt this structure. p.G435S FX was also predicted to be synthesized and exist in the cytoplasm, but not to be secreted into culture media by a cDNA expression assay. These two mutations may be responsible for the type 1 (null levels of both activity and antigen in plasma) FX deficiency with severe bleeding phenotype.
一名10日龄男婴因严重脐部出血被转诊至我院。凝血酶原时间（PT）和活化部分凝血活酶时间（APTT）显著延长。血浆凝血因子X（FX）活性和抗原水平分别为1%和0.6%。对其白细胞进行DNA序列分析发现为复合杂合状态；外显子6中已知的甘氨酸244突变为精氨酸（p.G244R），外显子8中有一个新的突变，即甘氨酸435突变为丝氨酸（p.G435S）。家系分析表明，p.G244R来自父系，而p.G435S来自母系。p.G244R突变先前已作为FX报道，这种突变蛋白被合成为非分泌性蛋白。在包括凝血酶、FVII、蛋白C、纤溶酶、胰蛋白酶和胰凝乳蛋白酶在内的胰蛋白酶样丝氨酸蛋白酶家族中，C末端区域氨基酸位置435处的甘氨酸是完全保守的。在FX的三维结构模型中，甘氨酸435位于11条β链内，深埋在催化口袋的后部。因此，预期丝氨酸替代会破坏该结构。通过cDNA表达试验预测，p.G435S FX也会被合成并存在于细胞质中，但不会分泌到培养基中。这两种突变可能是导致该1型（血浆中活性和抗原水平均为零）FX缺乏伴严重出血表型的原因。
