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Gene

TOP3A

DNA topoisomerase III alpha

Summary

Cytogenetic location
17p11.2
Coordinates
Chromosome 17: 18,271,428–18,314,994 (GRCh38)
Exons
19 exons across 43.6 kb
Protein
1,001 amino acids
Also known as
ZGRF7
Previous symbols
TOP3
MANE Select transcript
ENST00000321105.10NM_004618.5
Locus type
gene with protein product
  • Very high
  • Confident
  • Low
  • Very low

Reference genomeGRCh38

Positions on gene and variant pages follow this choice, in this browser.

Curated report relevant to this gene

  • Primary Mitochondrial Disease

    • Progressive External Ophthalmoplegia with Mitochondrial DNA Deletions

      Caused by variants in nuclear genes such as POLG, TWNK, SLC25A4 and RRM2B that lead to multiple mitochondrial DNA deletions, causing drooping eyelids, weak eye movements and muscle weakness, usually in adulthood.

      • 1 GenCC submitter rates it definitive or strong
      What knowing changes

      Knowing guides monitoring of eye, heart and swallowing function and avoidance of valproate in POLG disease.

How TOP3A is laid out

  • Coding sequence
  • Untranslated region
  • Intron
  • Direction of transcription
  • Known disease-causing sites
  • Stretches short reads find hard
Chromosome 17, with a bracket where TOP3A sits. TOP3A and 20 genes near it on chromosome 17, from 17,793,211 to 18,793,210.Chromosome 1717p11.2p13.3p13.2p13.1p12p11.2p11.1q11.1q11.2q12q21.1q21.2q21.31q21.32q21.33q22q23.1q23.2q23.3q24.1q24.2q24.3q25.1q25.2q25.317.8 Mb18 Mb18.2 Mb18.4 Mb18.6 MbRAI1: 17,681,323–17,811,453, forward strandRAI1SREBF1: 17,810,399–17,837,035, reverse strandSREBF1TOM1L2: 17,843,507–17,972,470, reverse strandTOM1L2DRC3: 17,972,813–18,016,889, forward strandDRC3ATPAF2: 17,977,409–18,040,833, reverse strandATPAF2GID4: 18,039,371–18,068,405, forward strandGID4DRG2: 18,087,876–18,107,979, forward strandDRG2MYO15A: 18,108,756–18,179,802, forward strandMYO15AALKBH5: 18,183,034–18,209,954, forward strandALKBH5LLGL1: 18,225,542–18,244,876, forward strandLLGL1FLII: 18,244,782–18,260,420, reverse strandFLIIMIEF2: 18,259,527–18,266,552, forward strandMIEF2TOP3A: 18,271,428–18,314,994, reverse strandTOP3ASMCR8: 18,315,293–18,328,056, forward strandSMCR8SHMT1: 18,327,686–18,363,562, reverse strandSHMT1EVPLL: 18,377,674–18,389,652, forward strandEVPLLLGALS9C: 18,476,737–18,494,945, forward strandLGALS9CTBC1D28: 18,634,247–18,644,427, reverse strandTBC1D28FOXO3B: 18,667,629–18,682,314, reverse strandFOXO3BFBXW10: 18,744,026–18,779,349, forward strandFBXW10TVP23B: 18,781,111–18,806,772, forward strandTVP23BDiagram of TOP3A: 19 exons on the reverse strand of chromosome 17Exon 18: 2 known disease-causing sitesExon 11: 1 known disease-causing siteExon 8: 2 known disease-causing sitesExon 6: 1 known disease-causing siteExon 19: 18,271,428–18,274,980, 3,553 basesExon 18: 18,277,675–18,278,357, 683 basesExon 17: 18,280,536–18,280,658, 123 basesExon 16: 18,282,698–18,282,841, 144 basesExon 15: 18,285,142–18,285,307, 166 basesExon 14: 18,285,407–18,285,520, 114 basesExon 13: 18,290,557–18,290,686, 130 basesExon 12: 18,290,842–18,291,027, 186 basesExon 11: 18,292,645–18,292,852, 208 basesExon 10: 18,294,703–18,294,785, 83 basesExon 9: 18,299,559–18,299,633, 75 basesExon 8: 18,301,885–18,301,985, 101 basesExon 7: 18,302,264–18,302,434, 171 basesExon 6: 18,302,580–18,302,723, 144 basesExon 5: 18,305,112–18,305,220, 109 basesExon 4: 18,306,891–18,306,966, 76 basesExon 3: 18,308,351–18,308,424, 74 basesExon 2: 18,308,882–18,308,941, 60 basesExon 1: 18,314,599–18,314,994, 396 bases191816141210864215′3′

Exons of the gene's MANE Select transcript (release v1.5), from NCBI and EMBL-EBI, on the GRCh38 reference genome.

Chromosome bands from UCSC's GRCh38 ideogram (2022-10-29).

Nearby genes from Ensembl release 116, on GRCh38.

Exons make up 6.6 kb of the gene's 43.6 kb; 3,006 of those bases code for the protein.

How a genome test reads TOP3A

6

positions in TOP3A where ClinVar classes a change as pathogenic or likely pathogenic

None of them falls in a region short reads find hard.

A whole genome covers all 43.6 kb of TOP3A, introns included, not only the 6.6 kb of exons.

Where this comes from

  • HGNC: the gene's symbol, name, other symbols and location.
  • MANE Select v1.5, from NCBI and EMBL-EBI: the transcript, its exons and coding sequence.
  • GenCC and ClinGen, released 2026-10-16: which conditions the gene is linked to, and how strongly.
  • The ACMG secondary findings list, SF v3.2.
  • ClinVar and the GIAB stratifications: known disease-causing sites, and the regions short reads find hard.
  • The Human Phenotype Ontology, release 2026-09-01: the traits linked to the gene. Find out more at hpo.jax.org.
  • Data release 2026.10.16-c6eea6bf.

Cite this page

APA

Dante Labs. (n.d.). TOP3A gene: DNA topoisomerase III alpha. Retrieved 16 October 2026, from https://dantelabs.com/genes/top3a

Vancouver

Dante Labs. TOP3A gene: DNA topoisomerase III alpha [Internet]. [cited 16 October 2026]. Available from: https://dantelabs.com/genes/top3a

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