Gene / locus
- Isochromosome 17q (i17q) is a structural chromosome 17 abnormality with loss of the short arm (17p) and duplication of the long arm (17q) due to a breakpoint at 17p11.2.
- It may arise from transverse instead of longitudinal division of the centromere during cell division or, more often, by an isochromatid break and fusion of the daughter chromatids above the centromere
- This leads to hemizygous loss of genes on 17p (including TP53 at 17p13.1) and gain of genes on 17q (e.g. WIP1/PPM1D at 17q23) rather than involving a single defined gene locus.
Normal function
- 17p13.1 region encodes tumor suppressor TP53, critical for DNA-damage response, cell-cycle arrest, and apoptosis.
- Amplification via i(17q) increases dosage of such proto‑oncogenes, including WIP1, which negatively regulates p53 signaling.
- 17q contains multiple genes with roles in proliferation and survival;
Mutation effects
- Formation of i(17q) causes obligatory loss of one TP53 allele with concurrent gain of 17q material, disturbing the p53 pathway and enhancing genomic instability.
- i17q
- Often occurs within complex karyotypes, frequently as dicentric isochromosomes
- Associated with disease progression and aggressive clinical behaviour in haematologic malignancies and brain tumors.
Clinical associations
- Medulloblastoma, non-WNT/non-SHH, group 4
- i(17q) is one of the most common cytogenetic abnormalities and can confer adverse prognosis in poor‑risk paediatric medulloblastoma.
- Reported in additional tumors such as pineoblastoma and neuroblastic tumors, supporting its role in a broader group of primitive neuroectodermal neoplasms.
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