Maternal microchimerism in a 2-years old boy with IL2R gamma chain deficiency

Abstract

BackgroundAccording to the literature, 40% of patients with SCID have maternal microchimerism. MethodsWe reported a case of a 2-year-old boy with X-linked SCID caused by a mutation in the IL2RG gene. ResultsTo search for a donor and subsequent HSCT, HLA genotyping of leukocytes from peripheral blood for class I and II by SBT method was performed. The HLA-I results were as follows: A*02:01,03:01,B*07:02,18:01, C*05:01,07:02. The results for class II were questionable, as an additional allele was identified at the DQB1 locus.To exclude contamination, typing was carried out with another sample of leukocytes. The result was a complete confirmation of the primary data for class I; for class II, the result could not be interpreted. To exclude the admixture of maternal lymphocytes in the patient’s peripheral blood samples, HLA genotyping of the buccal epithelium was performed: it turned out to be impossible to identify alleles at the DQB1 and DRB1 loci. Subsequently, it turned out that the child was periodically breastfed, which could cause the presence of maternal cells in the buccal epithelium.From all of the above, it is likely that problems in identifying the patient’s HLA genotype could be related to the phenomenon of maternal microchimerism.To differentiate chimerism from mosaicism, a molecular genetic analysis of STR loci of the patient and his parents was performed. The results demonstrated that the patient’s blood sample contained an admixture of maternal cells, indicating the presence of maternal microchimerism. Molecular genetic study data confirmed the results of cytogenetic analysis by FISH. The study of lymphocytes from the patient’s peripheral blood and bone marrow revealed that 49% and 92% of the cells, respectively, had a karyotype XX. Buccal epithelium was examined to exclude the constitutional nature of mosaicism by sex chromosomes: it was found that all buccal epithelial cells had a karyotype XY.After the results of the cytogenetic study, we repeated HLA typing of buccal epithelium DQB1 and DRB1 loci. The following results were obtained during genotyping: DRB1*03:01,11:01,DQB1*02:01,03:01, thus the patient’s HLA genotype was established.Results of the analysis of short tandem repeats (STR loci) of the patient and his parentsStudied loci DNABlood sampleBuccal epithelium sample of patientfather№allele/№allelemothers№allele/№allelepatient№allele/№allelefor a period of breastfeeding№allele/№allelewithout maternal cells№allele/№alleleD3S135815/1714/1814/17/18*14/17/18*14/17vWA17/1717/1917/17/19*17/17/19*17/17D16S53910/1311/1210/11/12*10/11/12*10/11D2S133821/2418/2518*/21/2518*/21/2521/25amelogeninXYXXXYXYXYD8S117912/1210/1210/1210/1210/12D21S1129/3029/30.229/30/30.2*29/30/30.2*29/30D18S5111/1812/1811/12*/1811/12*/1811/18D19S43315/1614/1514*/15/1514*/15/1515/15TH016/97/76/76/76/7FGA22/2421/2221/22*/2421/22*/2421/24*additional allele.Results of HLA-genotyping of the patient and his parentsInvestigation of the HLA- lociGenotype of the fatherGenotype of the motherGenotype of the patientHLA-AA*03:01, 24:02A*02:01, 23:01A*02:01, 03:01HLA-BB*07:02,15:17B*18:01, 51:01B*07:02,18:01HLA-CC*07:01, 07:02C*05:01,15:02C*05:01, 07:02HLA-DRB1DRB1* 11:01, 11:03DRB1* 01:01, 03:01DRB1* 03:01, 11:01HLA-DQB1DQB1* 03:01, 03:01DQB1* 02:01, 05:01DQB1* 02:01, 03:01 ConclusionsThe presence of maternal microchimerism can make it difficult to perform HLA genotyping in patients with SCID.