CNVKit does not output all the accessible regions in the targets bed file

Question

This question was also asked on Biostars

I am using CNVkit on my data using hg38 as reference. The command that I am using is the following:

cnvkit.py batch sample.bam  -n control.bam -m wgs -f reference.fasta  --target-avg-size 1000 --output-dir results/

So, on the CNVkit documentation page is reported that

The batch --method wgs option uses the given reference genome’s sequencing-accessible regions (“access” BED) as the “targets” – these will be calculated on the fly if not provided.

Problem is, when it calculates accesibile regions from the reference, there are a lot of them listed in the log file that are not present in the final .bed output, and I cannot figure out why. Accessible regions are later divided in bins, and bins without enough coverage are discarded later in the process. These are the outputs I get on a short example:

Log file:

WGS protocol: recommend '--annotate' option (e.g. refFlat.txt) to help locate genes in output files.
NC_000001.10: Scanning for accessible regions
      Accessible region NC_000001.10:10000-177417 (size 167417)
      Accessible region NC_000001.10:227417-267719 (size 40302)
      Accessible region NC_000001.10:317719-471368 (size 153649)
      Accessible region NC_000001.10:521368-2634220 (size 2112852)
      Accessible region NC_000001.10:2684220-3845268 (size 1161048)
      Accessible region NC_000001.10:3995268-13052998 (size 9057730)
      Accessible region NC_000001.10:13102998-13219912 (size 116914)
      Accessible region NC_000001.10:13319912-13557162 (size 237250)
      Accessible region NC_000001.10:13607162-17125658 (size 3518496)
      Accessible region NC_000001.10:17175658-29878082 (size 12702424)
      Accessible region NC_000001.10:30028082-103863906 (size 73835824)
      Accessible region NC_000001.10:103913906-120697156 (size 16783250)
      Accessible region NC_000001.10:120747156-120936695 (size 189539)
      Accessible region NC_000001.10:121086695-121485434 (size 398739)
      Accessible region NC_000001.10:142535434-142731022 (size 195588)
      Accessible region NC_000001.10:142781022-142967761 (size 186739)
      Accessible region NC_000001.10:143117761-143292816 (size 175055)
      Accessible region NC_000001.10:143342816-143544525 (size 201709)
      Accessible region NC_000001.10:143644525-143771002 (size 126477)
      Accessible region NC_000001.10:143871002-144095783 (size 224781)
      Accessible region NC_000001.10:144145783-144224481 (size 78698)
      Accessible region NC_000001.10:144274481-144401744 (size 127263)
      Accessible region NC_000001.10:144451744-144622413 (size 170669)
      Accessible region NC_000001.10:144672413-144710724 (size 38311)
      Accessible region NC_000001.10:144810724-145833118 (size 1022394)
      Accessible region NC_000001.10:145883118-146164650 (size 281532)
      Accessible region NC_000001.10:146214650-146253299 (size 38649)
      Accessible region NC_000001.10:146303299-148026038 (size 1722739)
      Accessible region NC_000001.10:148176038-148361358 (size 185320)
      Accessible region NC_000001.10:148511358-148684147 (size 172789)
      Accessible region NC_000001.10:148734147-148954460 (size 220313)
      Accessible region NC_000001.10:149004460-149459645 (size 455185)
      Accessible region NC_000001.10:149509645-205922707 (size 56413062)
      Accessible region NC_000001.10:206072707-206332221 (size 259514)
      Accessible region NC_000001.10:206482221-223747846 (size 17265625)
      Accessible region NC_000001.10:223797846-235192211 (size 11394365)
      Accessible region NC_000001.10:235242211-248908210 (size 13665999)
      Accessible region NC_000001.10:249058210-249240621 (size 182411)
NT_113878.1: Scanning for accessible regions
      Accessible region NT_113878.1:0-106433 (size 106433)
NT_167207.1: Scanning for accessible regions
      Accessible region NT_167207.1:0-547496 (size 547496)
NC_000002.11: Scanning for accessible regions
      Accessible region NC_000002.11:10000-3529312 (size 3519312)
      Accessible region NC_000002.11:3579312-5018788 (size 1439476)
      Accessible region NC_000002.11:5118788-16279724 (size 11160936)
      Accessible region NC_000002.11:16329724-21153113 (size 4823389)
      Accessible region NC_000002.11:21178113-31705550 (size 10527437)
      Accessible region NC_000002.11:31705551-31725939 (size 20388)
      Accessible region NC_000002.11:31726790-31816827 (size 90037)
      Accessible region NC_000002.11:31816828-31816854 (size 26)
      Accessible region NC_000002.11:31816855-31816858 (size 3)
      Accessible region NC_000002.11:31816859-33092197 (size 1275338)
      Accessible region NC_000002.11:33093197-33141692 (size 48495)
      Accessible region NC_000002.11:33142692-87668206 (size 54525514)
      Accessible region NC_000002.11:87718206-89630436 (size 1912230)
      Accessible region NC_000002.11:89830436-90321525 (size 491089)
      Accessible region NC_000002.11:90371525-90545103 (size 173578)
      Accessible region NC_000002.11:91595103-92326171 (size 731068)
      Accessible region NC_000002.11:95326171-110109337 (size 14783166)
      Accessible region NC_000002.11:110251337-149690582 (size 39439245)
      Accessible region NC_000002.11:149790582-234003741 (size 84213159)
      Accessible region NC_000002.11:234053741-239801978 (size 5748237)
      Accessible region NC_000002.11:239831978-240784132 (size 952154)
      Accessible region NC_000002.11:240809132-243102476 (size 2293344)
      Accessible region NC_000002.11:243152476-243189373 (size 36897)
NC_000003.11: Scanning for accessible regions
      Accessible region NC_000003.11:60000-17137943 (size 17077943)
NT_113878.1: Joining over small gaps
NT_167207.1: Joining over small gaps
Wrote GCF_000001405.25_GRCh37.p13_genomic.bed with 2 regions

So, multiple accessible regions are present for sequences NC_000001.10 , NC_000002.11 and NC_000003.11, but only regions for NT_113878.1 and NT_167207.1 are reported:

NT_113878.1     0       106433
NT_167207.1     0       547496

Why is that so? I cannot really figure out.

I am sure the missed regions have data, because I am also using another CNVs caller on the same exact data, and it shows high coverage for the same regions CNVkit is discarding. Also the coverage for control data is high in those discarder regions, so this shouldn't be the matter, but I have no ideas at this point.

EDIT: The question was answered on Biostars. Looking into the code, CNVkit is skipping chromosomes which don't have canonical names, like 'NCs' (so, the fact that it outputs the 'NTs' chromosomes is kind of incorrect, because they're also non-canonical and they should be skipped).

Answer 1

The OP received an answer on their question on Biostars:

The question was answered on Biostars. Looking into the code, CNVkit is skipping chromosomes which don't have canonical names, like 'NCs' (so, the fact that it outputs the 'NTs' chromosomes is kind of incorrect, because they're also non-canonical and they should be skipped).