By Kevin E. Noonan —
Myriad Genetics, one of the preeminent gene-based
diagnostics companies, has been targeted by the American Civil Liberties Union,
Dan Ravicher’s PUBPAT Organization, a raft of medical researchers and their
associations, and individual patients in a lawsuit filed in the Southern
District of New York; the avowed aim of the plaintiffs is to get the issue of "gene
patenting" before the U.S. Supreme Court (see "Association for Molecular Pathology v. U.S. Patent and Trademark Office"). While
the case wends its way through the Federal judicial system, Myriad is
continuing its pursuit of diagnostically-relevant cancer markers, the most
recent of which is a gene related to susceptibility to pancreatic cancer licensed
from the Johns Hopkins University.
The gene encodes PALB2, a tumor suppressor gene
reported to be involved in susceptibility to pancreatic cancer in the April 10,
2009 issue of Science (Jones et al., 2009, "Exomic Sequencing Identifies PALB2 as a Pancreatic Cancer Susceptibility Gene," Science 324: 217). The product of the PALB2 gene is
a binding partner of BRCA2, originally identified by its association with breast
cancer susceptibility. The two
gene products bind to DNA to repair damage, wherein PALB2 localizes and anchors
BRCA2 to damaged DNA in the cell nucleus. More than 3% of familial pancreatic cancer patients had mutations in PALB2
resulting in the production of a truncated version of the encoded protein. In contrast, no mutations in the PALB2 gene
were found in more than 1,000 normal DNA samples.
Myriad contends that the predictive value of
detecting such mutations are due to a 10- to 20-fold increase in the likelihood
of developing pancreatic cancer by age 70 for individuals bearing the PALB2 mutation
(or mutations in BRCA2 or another tumor suppressor gene, p16). Early detection is particularly
important for pancreatic cancer, which is typically detected only after it has
progressed past the stage where intervention has any chance of significantly
prolonging life. Pancreatic cancer
is diagnosed in about 200,000 patients worldwide each year, and is fatal almost
without exception.
The scope of the difficulty in identifying reliable
diagnostic genes is reflected in the following synopsis of the extent of
mutations found by the Johns Hopkins researchers in tumor DNA from one
pancreatic cancer patient.
Among the
20,661 coding genes analyzed, we identified 15,461 germline variants in Pa10
not found in the reference human genome. Of these, 7318 were synonymous, 7721
were missense, 64 were nonsense, 108 were at splice sites, and 250 were small
deletions or insertions (54% in-frame).
The PALB2 mutation found in tumor DNA from this
patient exhibited a germline deletion of four basepairs (TTGT) that produced a frameshift mutation at codon 58,
resulting in production of a truncated gene product from this gene. Additional mutations found associated
with pancreatic cancer in the PALB2 gene are a G > T transversion at the 5'
splice site of exon 6, a deletion of an A residue in exon 11 (at nucleotide
3116) and a C > T transition mutation in exon 12 (at nucleotide 3256). Fine structure mapping of mutations
found in the PALB2 gene in pancreatic cancer, breast cancer, and Fanconi anemia
patients was also reported.
The company estimates that a diagnostic genetic
test might be on the market by 2010.

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