| FAP |
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By
Miriam Komaromy,
MD
Reviewed
by Peggy Conrad,
MS, CGC and Jonathan
Terdiman, MD
Last updated August 4, 2000
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Once
a member of your immediate or extended family has been
diagnosed with the hereditary colon cancer syndrome familial
adenomatous polyposis (FAP) you may want to find out
whether you, your children or other members of your family
are at risk for the syndrome. To do this, you will need
to document your family medical history. Genetic professionals
call this making a pedigree, you might think of it as
drawing a family tree. This is where you'll find the vital
clues that can help sort out whether your family is at
risk for the syndrome and help you determine which family
members at risk should consider screening and genetic
tests to clarify their FAP status. To help you understand
how this process works, let's take a look at one FAP family's
pedigree, that of the Lopez family. |
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Risk and the Lopez Family
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Lydia
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| When
Lydia Lopez developed colon cancer symptoms at age 42,
she underwent a colonoscopy, which revealed not only colon
cancer but the hundreds of colon polyps
characteristic of FAP.
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Knowing that Lydia has FAP, we can now look for clues in her family tree that identify other people with FAP — even people that may not have been diagnosed while they were alive. Take Lydia's mother, Maria, and her grandmother, Consuelo: Both died from colon cancer at extremely early ages. In light of Lydia's diagnosis, most medical professionals would assume that both mother and grandmother had the syndrome, which Lydia then inherited.
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Lydia's
Uncle and His Family
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If
you look at the pedigree, you'll see that Lydia's mother
had a brother, Juan, who could also have inherited FAP
from their mother (Consuelo). However, because Juan
is alive and well at 82, this scenario is unlikely,
since FAP patients commonly develop colon polyps at
a young age and, if they leave their polyps untreated,
often develop colon cancer by their mid-30s.
If
Juan does not have FAP, he could not have passed the syndrome
on to his children, which means they don't need to be
tested or screened for FAP. Instead, they should simply
follow the much less stringent colon cancer screening
guidelines recommended for the population at large —
that is, people with no family history of FAP. |
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Lydia's
Sister and Her Family
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As we continue to look
at the family tree, we see that among Lydia's siblings,
Dolores, at age 52, is also fairly unlikely to have
FAP since she has not yet developed any colon cancer
symptoms. However, since FAP patients vary tremendously
in the ages at which they develop polyps and symptoms,
Dolores should still undergo screening to confirm that
she is polyp-free.
If
Dolores' screening shows an absence of polyps, it's
very unlikely that she has FAP. And since Dolores' children
could only have inherited FAP if the syndrome was present
in their mother, most experts would agree that they
are not at risk for FAP and thus only need to follow
routine colon cancer screening guidelines.
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Lydia's
Brother and His Family
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| Because
Lydia's brother, José, is only 40 years old, he may have
FAP even though he has yet to manifest any symptoms. José
should therefore be immediately screened for colon cancer
via sigmoidoscopy. If his doctor finds polyps, he will
counsel José regarding surgical options to remove his
colon, since this is the only surefire way to prevent
the almost inevitable development of colon cancer in FAP
patients. If José does indeed have FAP, his children,
George and Carlos, are at risk as well — and at age
10, George is old enough to begin yearly screening by
sigmoidoscopy. |
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Lydia's
Children
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| Lydia has two children, both of whom are at high risk for FAP (each has a 50 percent chance of having inherited
FAP from Lydia). Both are old enough to begin having annual
sigmoidoscopies. |
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Genetic
Testing and the Lopez Family
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In
addition to providing clues about individual's
risk for FAP (and, correspondingly, colon cancer),
a family's medical history can also provide helpful
information about who should consider genetic
testing. Once again, let's take a look at the
Lopez family.
If
Lydia — who has already received a FAP diagnosis
— were to test positive for one of the genetic
mutations that cause FAP, other family members
could benefit enormously from the information.
For Lydia's children (Mark and Katherine) and
José's sons (George and Carlos), a negative
genetic test result could save them from years
of invasive screening procedures and cancer anxiety.
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If,
on the other hand, Lydia were to take a genetic test,
but no mutation was found, no one else in the family
could benefit from testing. This is because doctors
would have to assume that whatever genetic mutation
was causing the Lopez family's FAP was not detectable
using currently available genetic tests. Lydia's children,
and José's children, would then have to assume that
they are at high risk for FAP and follow the appropriate
screening procedures.
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| Genetic
testing for FAP must begin with a family member
who has been clinically diagnosed with the syndrome.
If this initial genetic test detects a mutation,
the genetic culprit for that family's FAP syndrome
has been identified and other family members can
now be tested to see if they carry the same mutation.
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