text: user9750: Is there an accepted boundary of the extended major histocompatibility complex (xMHC) in human? Specifically, I am interested in the boundary coordinates for Genome Reference Consortium Human Build 38 (GRCh38 / hg38).
  I'd like to use these coordinates to query MyGene.info to retrieve a list of genes in the xMHC. For example, King et al 2019 used the following definition:
  
  we excluded drugs with nonhuman or xMHC gene targets. We considered xMHC to include HIST1H2AA and KIFC1 and all genes between them (Chromosome 6 25.7 Mb-33.4 Mb).
  
  But I was curious whether there was an authoritative definition of the xMHC region in humans that would specify down the the base pair rather than just megabase pair.
  
  user9799: Here is one definition of the classical MHC region: https://www.ncbi.nlm.nih.gov/grc/human/regions/MHC?asm=GRCh38.p13
  which defines it as the 5mb region chr6:28510120-33480577 in GRCh38 coordinates.
  The "extended MHC" defined here [1] is 7.2 mb and encompasses an additional "extended Class I" region upstream of the region given above. The xMHC is defined in [1] as the regions between HIST1H2AA and RPL12P1 genes, which would give you chr6:25726063-33400644 in Grch38. This is very similar to your HIST1H2AA - KIFC1 definition (chr6:25726063-33410226). Of course if you're trying to reproduce a result, probably better to use the original paper's definition.
  [1] https://www.nature.com/articles/nrg1489
  
original_text: 9750: <p>Is there an accepted boundary of the <em>extended</em> major histocompatibility complex (xMHC) in human? Specifically, I am interested in the boundary coordinates for Genome Reference Consortium Human Build 38 (GRCh38 / hg38).</p>
  <p>I'd like to use these coordinates to query MyGene.info to retrieve a list of genes in the xMHC. For example, King et al 2019 <a href="https://doi.org/10.1371/journal.pgen.1008489.s002" rel="nofollow noreferrer" title="S2 Data. Updating Pipeline Data: Supplementary Methods And Results">used</a> the following definition:</p>
  <blockquote>
  <p>we excluded drugs with nonhuman or xMHC gene targets. We considered xMHC to include HIST1H2AA and KIFC1 and all genes between them (Chromosome 6 25.7 Mb-33.4 Mb).</p>
  </blockquote>
  <p>But I was curious whether there was an authoritative definition of the xMHC region in humans that would specify down the the base pair rather than just megabase pair.</p>
   9799: <p>Here is one definition of the classical MHC region: <a href="https://www.ncbi.nlm.nih.gov/grc/human/regions/MHC?asm=GRCh38.p13" rel="nofollow noreferrer">https://www.ncbi.nlm.nih.gov/grc/human/regions/MHC?asm=GRCh38.p13</a></p>
  <p>which defines it as the 5mb region chr6:28510120-33480577 in GRCh38 coordinates.</p>
  <p>The &quot;extended MHC&quot; defined here [1] is 7.2 mb and encompasses an additional &quot;extended Class I&quot; region upstream of the region given above. The xMHC is defined in [1] as the regions between <em>HIST1H2AA</em> and <em>RPL12P1</em> genes, which would give you chr6:25726063-33400644 in Grch38. This is very similar to your HIST1H2AA - KIFC1 definition (chr6:25726063-33410226). Of course if you're trying to reproduce a result, probably better to use the original paper's definition.</p>
  <p>[1] <a href="https://www.nature.com/articles/nrg1489" rel="nofollow noreferrer">https://www.nature.com/articles/nrg1489</a></p>
  