docs: def delete_variants(adapter, vcf_obj, case_obj, case_id=None):
      """Delete variants for a case in the database
      
      Args:
          adapter(loqusdb.plugins.Adapter)
          vcf_obj(iterable(dict))
          ind_positions(dict)
          case_id(str)
      
      Returns:
          nr_deleted (int): Number of deleted variants
      """
      case_id = case_id or case_obj['case_id']
      nr_deleted = 0
      start_deleting = datetime.now()
      chrom_time = datetime.now()
      current_chrom = None
      new_chrom = None
      
      for variant in vcf_obj:
          formated_variant = build_variant(
              variant=variant,
              case_obj=case_obj,
              case_id=case_id,
          )
          
          if not formated_variant:
              continue
          
          new_chrom = formated_variant.get('chrom')
          adapter.delete_variant(formated_variant)
          nr_deleted += 1
          
          if not current_chrom:
              LOG.info("Start deleting chromosome {}".format(new_chrom))
              current_chrom = new_chrom
              chrom_time = datetime.now()
              continue
          
          if new_chrom != current_chrom:
              LOG.info("Chromosome {0} done".format(current_chrom))
              LOG.info("Time to delete chromosome {0}: {1}".format(
                  current_chrom, datetime.now()-chrom_time))
              LOG.info("Start deleting chromosome {0}".format(new_chrom))
              current_chrom = new_chrom
  
  
      return nr_deleted