Monday, February 8, 2016

Does Aneuploidy Precede Cancer: An Answer Comes from a Rare Disease

The presence of an abnormal number of chromosomes (for the species) in a cell. Most cancers contain aneuploid cells; an observation that holds true for virtually every poorly differentiated cancer. Aneuploidy is seen less often in benign tumors and well-differentiated tumors. Aneuploidy is also found in epithelial precancers and other growing lesions that can sometimes regress spontaneously (e.g. keratoacanthoma). These observations have prompted speculation that the acquisition of aneuploidy is an underlying cause of the cancer phenotype (i.e., tumor growth, invasion into surrounding tissues, and metastases). Such causal associations invite skepticism, particularly in the realm of cancer biology, as virtually every cellular process and constituent of cancer cells has been shown to deviate from the norm. Nonetheless, there is good reason to suspect that aneuploidy is at least a factor in tumor development, as mutations that cause aneuploidy are associated with a heightened increased risk of cancer (e.g., Brca1 gene mutations (1), and mutations of mitotic checkpoint genes (2)). Others have warned that aneuploidy, by itself, may not cause cancer (3). Aneuploidy may need to be accompanied by other factors associated with genetic instability, such as the accumulation of DNA damage, cytogenetic abnormalities, and reduced cell death (3). As usual, a rare disease helps to clarify the role of aneuploidy in carcinogenesis. Mosaic variegated aneuploidy syndrome-1 (MVA1) is caused by a homozygous or compound heterozygous mutation in the BUB1B gene, which encodes a key protein in the mitotic spindle check point. This disease is characterized by widespread aneuploidy in more than 25% of the cells of the body, and a heightened risk of developing childhood cancers (e.g., rhabdomyosarcoma, Wilms tumor, and leukemia). Because the underlying cause of mosaic variegated aneuploidy syndrome-1 is a gene that produces aneuploidy, and because such aneuploidy is an early event (i.e., congenital), that precedes the development of cancer and that is found in the developed cancer cells, then it is reasonable to infer that aneuploidy is closely associated with events that lead to cancer.

[1] Xu X, Weaver Z, Linke SP, Li C, Gotay J, Wang XW, et al. Centrosome amplification and a defective G2-M cell cycle checkpoint induce genetic instability in BRCA1 exon 11 isoform-deficient cells. Mol Cell 3:389-395, 1999.

[2] Cahill DP, Lengauer C, Yu J, Riggins GJ, Willson JK, Markowitz SD, et al. Mutations of mitotic checkpoint genes in human cancers. Nature 392:300-303, 1998.

[3] Weaver BAA, Cleveland DW. The role of aneuploidy in promoting and suppressing tumors.The Journal of Cell Biology 185:935-937, 2009.

- Jules Berman (copyrighted material)

key words: rare disease, orphan drugs, orphan diseases, zebra diseases, rare disease day, jules j berman

Rare Disease Day is coming up February 29 (a rare day for rare diseases). In honor of the upcoming event, I'll be posting blogs all month, related to the rare diseases and to rare disease funding.