HLA 定序分型在異質性消失（LOH）時的解決方案

Strategy for Loss of Heterozygosity (LOH) in HLA Sequence-based Typing (SBT)

在多種腫瘤及白血病病人有可能發生HLA的異質性消失（loss of heterozygosity ; LOH），一位診斷為AML的女士，執行HLA定序分型以尋找適合的捐贈者。第一次送檢Blast：52.0%，HLA定序分型結果除HLA- DQB1是heterozygous外，其餘loci均為homozygous。因HLA- DQB1定序序列中，兩個型別訊號強度有差異，因此懷疑其餘homozygous loci發生LOH。第二次送檢Blast：1.0%，HLA定序分型結果除HLA-DRB1、DQB1是heterozygous外，此次HLA-A、B、C loci仍為homozygous。由父母的HLA分型結果發現，病人來自母親的HLA-A、B、C三個loci發生LOH。以針對母親HLA-A，B，C型別有特異性的引子（GSA；group specific primer）對病人檢體進行PCR擴增，再進行定序分析終於得到病人正確型別。因此建議臨床上，白血病病患執行HLA 定序，如分型結果有部分loci為homozygous，且heterozygous loci中，兩個型別訊號強度有差異時，應搭配親屬之HLA分型結果，以釐清分型究竟是homozygous或是發生LOH。 Loss of heterozygosity (LOH) in HLA is a well-known phenomenon in solid tumors and leukemiapatients. A woman diagnosed with acute myelomonocytic leukemia; executed HLA sequence-basedtyping (SBT) for finding an appropriate donor. In first detection, the peripheral blast cell was 52%and HLA SBT revealed homozygosity except HLA-DQB1 locus. We found signal strength showsdifference between two alleles in HLA-DQB1 sequence, so LOH in HLA might happen. In seconddetection, the peripheral blast cell was 1%. The homozygous results of HLA-A, -B, -C still reportedexcept HLA-DQB1 and –DRB1. However, HLA typing results of her parents indicated that sheindeed lost her maternal alleles of HLA-A, -B, and -C loci. We further used the HLA group specificprimers (GSA) for the maternal alleles, and finally demonstrated patient was heterozygous at allHLA loci. Therefore recommend, if the HLA-SBT results for leukemia patient appear homozygousin some loci, and signal strength has a difference between two alleles in heterozygous loci. It shouldcombine with the HLA-SBT data of relatives. To clarify the homozygous loci are true homozygosityor LOH.

Loss of heterozygosity (LOH) in HLA is a well-known phenomenon in solid tumors and leukemiapatients. A woman diagnosed with acute myelomonocytic leukemia; executed HLA sequence-basedtyping (SBT) for finding an appropriate donor. In first detection, the peripheral blast cell was 52%and HLA SBT revealed homozygosity except HLA-DQB1 locus. We found signal strength showsdifference between two alleles in HLA-DQB1 sequence, so LOH in HLA might happen. In seconddetection, the peripheral blast cell was 1%. The homozygous results of HLA-A, -B, -C still reportedexcept HLA-DQB1 and –DRB1. However, HLA typing results of her parents indicated that sheindeed lost her maternal alleles of HLA-A, -B, and -C loci. We further used the HLA group specificprimers (GSA) for the maternal alleles, and finally demonstrated patient was heterozygous at allHLA loci. Therefore recommend, if the HLA-SBT results for leukemia patient appear homozygousin some loci, and signal strength has a difference between two alleles in heterozygous loci. It shouldcombine with the HLA-SBT data of relatives. To clarify the homozygous loci are true homozygosityor LOH.