25-OR: LOSS OF HETEROZYGOSITY IN PATIENT WITH ACUTE MYELOCYTIC LEUKEMIA (AML)

Aim Chromosomal abnormality which may down regulate the human leukocyte antigen (HLA) on chromosome 6 may result in inaccurate homozygous typing of a patient and thus adversely affect donor and recipient matching and transplant outcome. We present a case of a 60 year old female with AML who had chromosomal abnormality in tumor cells. Methods HLA typing was performed by SSP, rSSO microarray and SBT. Short Tandem Repeat (STR) was performed using primers targeting 10 genetic loci. Results Initial typing on patient’s blood revealed the following: SSP method: A ∗ 32, weak bands for A ∗ 2; B ∗ 51, weak bands of B ∗ 44; C ∗ 01, weak band of C ∗ 12, DRB1 ∗ 1301, weak band of 07:01; DRB3, weak band of DRB4; DQB1 ∗ 06:03, weak band of 02:02. rSSO (class I only): A ∗ 02:XX, 32:XX; B ∗ 51:XX, C ∗ 01:XX. SBT (class I only): A ∗ 32:01, 32:01; B ∗ 51:01, 51:01; C ∗ 01:01, 01:01. Since SSP showed presence of a second haplotype with weak bands, and rSSO detected two A locus antigens, HLA typing was questionable and thought that could be due to transfusion or chromosomal abnormality. HLA typing was repeated using patient’s buccal swab. Results of both SSP and SBT confirmed heterozygosity (mentioned above) with strong bands in all loci in SSP and amplification of both haplotypes in SBT. rSSO typing was not performed on buccal swab. Short tandem repeat (STR) profiles of blood and buccal swabs samples showed identical amplification for 10 primers used. Conclusions The above results show the loss of HLA genes on chromosome 6 in an AML patient. This abnormality was not included in 10 short tandem repeat we tested for. In this case, SSP method showed some weak amplification and helped us to address the possibility of chromosomal abnormality. HLA typing of buccal swab, blood at the time of remission or confirmatory typing must be considered to accurately type leukemia patients with possible chromosomal abnormality.