code: private String extractGeneSymbol(Xref xref)
  	{
  		if (xref.getDb() != null && (
  			xref.getDb().equalsIgnoreCase("HGNC Symbol") ||
  			xref.getDb().equalsIgnoreCase("Gene Symbol") ||
  			xref.getDb().equalsIgnoreCase("HGNC")))
  		{
  			String ref = xref.getId();
  
  			if (ref != null) {
  				ref = ref.trim();
  				if (ref.contains(":")) ref = ref.substring(ref.indexOf(":") + 1);
  				if (ref.contains("_")) ref = ref.substring(ref.indexOf("_") + 1);
  				// if the reference is an HGNC ID, then convert it to a symbol
  				if (!HGNC.containsSymbol(ref) && Character.isDigit(ref.charAt(0))) {
  					ref = HGNC.getSymbol(ref);
  				}
  			}
  
  			return ref;
  		}
  
  		return null;
  	}
docs: Searches for gene symbol in Xref.
  @param xref Xref to search
  @return gene symbol