Genesis of new allele at locus D2S1360 in leukemia patient

Genotyping polymorphic short tandem repeats (STRs) is widely used in forensic DNA analysis for genetic identification of individuals in paternity disputes or mapping genetic diseases. Another use of STRs is monitoring hematopoietic chimerism in patients after allogeneic hematopoietic stem cell transplantation (HSCT). STR profiling can be used for cell line authentication. STR polymorphism consists of many alleles per locus, each containing a different number of tandemly arranged repeat units. The number of repeats can be highly variable among individuals, which is suitable for human identification purposes. According to the Mendelian inheritance, each individual inherits one allele from the mother and another from the father at every locus. In rare cases, abnormal DNA profiles can be found, such as tri-allelic pattern. This genotyping irregularity is presented as a result of four nucleotides’ mutational changes, suggesting the loss or addition of one or more tetrameric repeat units [1]. Mutations in hematologic malignancies can also cause loss of heterozygosity (LOH) or different STR length mutations. Leukemia is a type of cancer affecting the blood or bone marrow cells, thus resultant mutations and loss of alleles can be observed in both blood tissue and other tumor tissues of the same individual. Differences in STR polymorphism in healthy and malignant tissues may lead to misinterpretation of leukemia patient's forensic samples. In the event of leukemia, the comparative analysis on buccal and blood samples as references should be performed [2,3]. It is also suitable to use hair follicles or semen [4]. In this article, we report a rare case of genesis of a novel allele of marker D2S1360 in a patient with acute myeloid leukemia. Changes in the profile of the patients were monitored over time and confirmed by sequencing analysis. The analyses were performed on DNA from peripheral blood (PB), bone marrow (BM) or buccal swab samples from a 47 year-old woman after HSCT. In 2001, she was diagnosed with polycytemia vera, the chronic myeloproliferative disease. In 2010, the patient’s status had evolved into post-polycytemia vera myelofibrosis, a high-risk disease, which was the cause of HSCT. Allogeneic HSCT was carried out in 2012 from HLA (human leukocyte antigen system) identical sibling (the patient's sister). Complete remission was achieved after HSCT. In the time period of 16–19 months after HSCT, the value of mixed chimerism (MC) moved into the range of 30–98% of recipient. Donor lymphocyte infusions (DLIs) were given to our patient for increasing MC, the patient received DLIs in escalating doses. The first DLI dose was 5 10 CD3þ cells/kg, the second dose was 1 10 CD3þ cells/kg, and the third dose was 5 10 CD3þ cells/kg. In next 10 months, the value of MC decreased and persisted under a level of 1% in the recipient. Then (since January 2016) in a period of 5 months, the value of MC increased to 72% in the recipient and the patient’s diagnosis was changed to acute myeloid leukemia by detecting 26% myeloblasts in BM in May 2016. The patient refused a second allogeneic HSCT and now she is being treated with palliative treatment (since September 2016). Informative STR polymorphism for routine monitoring of cell chimerism was determined using a multiplex test system MentypeR ChimeraR PCR Amplification Kit by Biotype (AG, Dresden, Germany), namely D2S1360 was selected. The recipient's (patient's) alleles contained 21 and 25 tetranucleotide repeats; alleles 23 and 30 were found in the DNA of the donor. Monitoring of chimerism was carried out in accordance with therapeutic protocols; the PB or BM samples were analyzed by fragment analysis using ABI3130xl Genetic Analyzer (Applied Biosystems, Foster City, CA). An MC increase over 1% of the recipient was first observed in January 2016 (26 months after HSCT). The same growth trend was evident in subsequent PB samples. The patient diagnosis was changed to acute myeloid leukemia by detecting myeloblasts in the BM (MC 14% of recipient, 27 months after HSCT). During the following period, the patient's PB samples were taken at regular intervals (once a month). The proportion of recipient alleles (21–25) gradually became more significant and except these alleles, the presence of