A novel HLA-B*420502 allele identified by PCR-SSO/SSP routine typing and confirmed by Sequencing-based typing

SNP-specific extraction of haplotype-resolved targeted genomic regions

The availability of genotyping platforms for comprehensive genetic analysis of complex traits has resulted in a plethora of studies reporting the association of specific single-nucleotide polymorphisms (SNPs) with common diseases or drug responses. However, detailed genetic analysis of these associated regions that would correlate particular polymorphisms to phenotypes has lagged. This is primarily due to the lack of technologies that provide additional sequence information about genomic regions surrounding specific SNPs, preferably in haploid form. Enrichment methods for resequencing should have the specificity to provide DNA linked to SNPs of interest with sufficient quality to be used in a cost-effective and high-throughput manner. We describe a simple, automated method of targeting specific sequences of genomic DNA that can directly be used in downstream applications. The method isolates haploid chromosomal regions flanking targeted SNPs by hybridizing and enzymatically elongating oligonucleotides with biotinylated nucleotides based on their selective binding to unique sequence elements that differentiate one allele from any other differing sequence. The targeted genomic region is captured by streptavidin-coated magnetic particles and analyzed by standard genotyping, sequencing or microarray analysis. We applied this technology to determine contiguous molecular haplotypes across a ∼150 kb genomic region of the major histocompatibility complex.

Identification of a novel HLA-DPB1 allele (DPB1*1902) by haplotype-specific extraction and nucleotide sequencing

The DPB1*1902 allele resulted from a single-nucleotide substitution at codon 35 (TTC --> CTC/F --> L) of exon 2 of DPB1*0402 or 0602.

Identification of a new HLA-B allele (B*1576) by haplotype specific extraction

Routine typing of a potential bone marrow donor by sequence-specific oligonucleotide probes (SSOP) and sequence based typing (SBT) produced inconclusive subtyping results, suggesting a new allele. A magnetic bead-based method, haplotype specific extraction (HSE), was used to separate the diploid sample into its haploid components. The sample was then re-typed using standard SBT, revealing a new human leukocyte antigen (HLA) allele, since named B*1576. HSE used in conjunction with standard SBT is a convenient and simple tool for resolving ambiguous and novel allele combinations without the need for amplification or subcloning.