The haplotype structure of the human major histocompatibility complex

Area of Science:

• Human genetics
• Genomic analysis
• Disease gene mapping

Background:

• Single-nucleotide polymorphisms (SNPs) and linkage disequilibrium (LD) are commonly used for localizing human disease genes.
• The human genome, including the major histocompatibility complex (MHC), is thought to consist of sequence blocks with random recombination between them.

Purpose of the Study:

• To evaluate the effectiveness of SNP/LD analysis in localizing human disease genes.
• To compare SNP/LD analysis with direct MHC haplotype determination.

Main Methods:

• Analysis of single-nucleotide polymorphisms (SNPs) and linkage disequilibrium (LD).
• Direct determination of major histocompatibility complex (MHC) haplotypes from family studies.
• Comparison of SNP/LD-defined blocks with conserved extended haplotypes (CEHs).

Main Results:

• Direct MHC haplotype analysis reveals conserved extended haplotypes (CEHs) spanning over 1 Mb, which differ in frequency among populations and in disease patients.
• SNP/LD analysis has limitations in detecting these CEHs due to its inability to assess DNA fixity beyond a few markers.
• Statistical analysis in SNP/LD methods fails to capture the detailed haplotype structure essential for gene localization.

Conclusions:

• SNP/LD analysis provides an oversimplified view of genomic structure, particularly in the MHC.
• Direct haplotype determination is essential for understanding haplotype structure and accurately localizing disease susceptibility genes.
• The limitations of SNP/LD analysis raise questions about its utility in comprehensive disease gene localization and identification.