P052 A rare DRB1 allele with exon 2–5 deletions

Abstract

A 4-month old SCID patient was worked up in HLA lab for hematopoietic stem cell transplant. DNA was extracted from blood samples for the patient and both parents. HLA typing for A, B, C, DRB1 and DQB1 was initially performed using a combination of high resolution rSSO and high resolution SSP. Family segregation analysis suggests that the child has inherited mother’s “c” haplotype with the exception of DRB1. The child was typed as DRB1∗01:02 homozygous and the mother was typed as DRB1∗01:01 homozygous. In addition, mother sample appears to have an uncommon association of DRB1∗01:01-DQB1∗06:02. Testing of DRB345 locus reveals that the mother also has an unusual DRB5∗01 associated with DRB1∗01:01 homozygosity. To rule out the possibility of potential rSSO failure of 2nd DRB1 allele detection (possibly due to initial PCR failure caused by primer binding complementary region mutations), we tried high resolution DRB1∗15 and DRB1∗16 SSP. Both gels reveal no positive reaction bands for all lanes other than internal controls. A send out NGS based DRB1 test targeting Exons 2 and 3 also agrees with our own typing and so is our own NGS based HLA typing targeting Exon 2, 3 and partial Exon 4 of DRB1 gene. Buccal swab samples from both the patient and the mother confirm HLA findings derived from DNA of blood origin. Initial conclusion was drawn that the patient and the mother likely carry a DRB1∗”Blank” which cannot be detected by current testing platforms. Finally, with the help from R&D department of GenDx, full-length DRB1 gene was amplified. A small size amplicon was noticed from both the patient and the mother DNA samples. NGS sequencing of the amplicons reveals the presence of a truncated DRB1 allele missing Exons 2–5 and the left over regions suggested likelihood of DRB1∗15 origin. Download : Download high-res image (145KB) Download : Download full-size image