Department of Pathophysiological Laboratory Sciences, Nagoya University Graduate School of Medicine, Nagoya Japan.
J Thromb Haemost. 2012 Oct;10(10):2099-107. doi: 10.1111/j.1538-7836.2012.04897.x.
Intron 22 inversion (Inv22) of the coagulation factor (F)VIII gene (F8) is a frequent cause of severe hemophilia A. In addition to Inv22, a variety of F8 mutations (1492 unique mutations) causing hemophilia A have been reported, of which 171 involve deletions of over 50 bp (HAMSTeRs database; http://hadb.org.uk/). However, only 10% of these large deletions have been fully characterized at the nucleotide level.
We investigated gene abnormalities in three unrelated severe hemophilia A patients with high titer FVIII inhibitors. They had previously been shown to carry large deletions of the F8, but the precise gene abnormalities remain to be elucidated.
Inverse shifting-PCR (IS-PCR) Inv22 diagnostic tests revealed that these patients carried either type I or II Inv22. However, they showed a wild-type (WT) pattern in the IS-PCR Inv22 complementary tests. We further analyzed their X chromosomes to account for the puzzling results, and found that they had different centromeric breakpoints in the Inv22 X chromosomes, adjacent to the palindromic regions containing int22h-2 or -3, and their spacer region, respectively. The connections appeared to be shifted towards the telomere of the WT F8 Xq28, resulting in a new telomere with an additional intact int22h copy.
These gene rearrangements might result from double-strand breaks in the most distal regions of the long arms of the Inv22 X chromosomes, followed by DNA restorations using the WT F8 Xq28 by non-homologous end joining or break-induced replication; thus leading to large F8 deletions in severe hemophilia A patients.
凝血因子 (F)VIII 基因 (F8) 内含子 22 倒位 (Inv22) 是严重血友病 A 的常见原因。除了 Inv22 之外，还报道了多种导致血友病 A 的 F8 突变（1492 个独特突变），其中 171 个涉及超过 50bp 的缺失（HAMSTeRs 数据库；http://hadb.org.uk/）。然而，这些大片段缺失仅有 10% 已经在核苷酸水平上得到了充分的表征。
我们研究了三个无关的严重血友病 A 患者的基因异常，他们的 FVIII 抑制剂效价高。他们之前曾被证实携带 F8 的大片段缺失，但确切的基因异常仍有待阐明。
Inv22 反向移位-PCR（IS-PCR）诊断测试表明，这些患者携带 I 型或 II 型 Inv22。然而，他们在 IS-PCR Inv22 互补测试中显示出 WT 模式。我们进一步分析了他们的 X 染色体，以解释这些令人困惑的结果，发现它们在 Inv22 X 染色体上具有不同的着丝粒断点，分别靠近含有 int22h-2 或 -3 的回文区域及其间隔区。这些连接似乎向 WT F8 Xq28 的端粒转移，导致新的端粒带有额外完整的 int22h 拷贝。
这些基因重排可能是由 Inv22 X 染色体长臂最远端的双链断裂引起的，随后通过非同源末端连接或断裂诱导复制，利用 WT F8 Xq28 进行 DNA 修复，从而导致严重血友病 A 患者的 F8 大片段缺失。
