chr9·hg38·138.4 Mb

Chromosome 9

Home to the most deleted gene in cancer, the translocation that launched targeted therapy, the blood group that defined transfusion medicine, and the largest block of autosomal heterochromatin — a chromosome of extremes.

Physical Properties

Length138.4 Mb

Centromeresubmetacentric

p-arm43.2 Mb

q-arm92.9 Mb

Genomic Features

Protein-coding genes786

Gene density5.7 / Mb

CpG islands12,098

EPIC v2 probes38,448

Notable

Largest genePTPRD (2.3 Mb)

Disease associations

Chronic myeloid leukemia

Melanoma

Tuberous sclerosis

· ABL1 forms the BCR-ABL1 fusion in chronic myeloid leukemia

· Contains the ABO blood group gene at 9q34.2

· 9p21.3 (CDKN2A) is the most frequently deleted locus in cancer

Genomic Architecture

Pericentromeric complexity — 9qh region consists of satellite I, II, III, and beta-satellite DNA. Different inversion types have distinct satellite compositions.

Type I interferon cluster — (9p21-22): 26 interferon genes/pseudogenes including 16 IFN-alpha genes.

9p21.3 GWAS hotspot — 59 SNPs with multiple long-range enhancers and lncRNAs. Most replicated genetic risk locus for cardiovascular disease AND associated with T2D and multiple cancers.

Evolutionary History

Ancient ohnologs — MHC region (chr6) has ohnologs on chr1, 9, and 19, all descending from pre-whole-genome-duplication chromosome 9 of the ancestral vertebrate (>450 Mya).

ABO polymorphism age — A and B alleles diverged before the human-chimpanzee split. Trans-species polymorphism maintained by balancing selection.

Deep Cuts

The Philadelphia chromosome launched precision oncology — The 41-year journey from cytogenetics (1960) to imatinib (2001) inaugurated molecularly targeted therapy.

9p21.3 is the most "multipurpose" risk locus — Independently associated with CAD, T2D, melanoma, glioma, and more through distinct mechanisms. No other locus has so many disease associations.

The O blood type is a broken A — The most common blood type worldwide results from a frameshift that destroys the entire protein, arising at least three times independently.

§ Deep dive

Pericentromeric complexity9qh region consists of satellite I, II, III, and beta-satellite DNA. Different inversion types have distinct satellite compositions.

Type I interferon cluster(9p21-22): 26 interferon genes/pseudogenes including 16 IFN-alpha genes.

9p21.3 GWAS hotspot59 SNPs with multiple long-range enhancers and lncRNAs. Most replicated genetic risk locus for cardiovascular disease AND associated with T2D and multiple cancers.