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What is Birt-Hogg-Dubé syndrome?
Birt-Hogg-Dubé syndrome (BHD) is a hereditary condition associated
with multiple noncancerous (benign) skin tumors, lung cysts, and an
increased risk of both benign kidney tumors and kidney cancer. Symptoms of BHD generally do not appear until adulthood.
The most common skin tumors in BHD are called fibrofolliculomas.
These are pale or flesh-colored tumors that occur in the hair follicles.
Other skin tumors associated with BHD are called trichodiscomas and
acrochordons. Acrochordons are also known as skin tags, and
trichodiscomas are a growth of normal-appearing tissue that builds up
into a noncancerous tumor. The lung cysts in BHD do not cause problems
with breathing and do not increase the risk of lung cancer. There is an
increased risk of spontaneous pneumothorax, which is air leaking out of
the lungs and into the chest. Spontaneous pneumothorax may result in a
collapsed lung. Many different types of kidney tumors have been seen in
people with BHD. Multiple tumors may occur on both kidneys. Tumors tend
to grow slowly, but they are likely to develop into kidney cancer.
What causes BHD?
BHD is a genetic condition. This means that the cancer risk and other
features of BHD can be passed from generation to generation in a
family. A specific gene called FLCN, which creates a protein called folliculin, is believed to cause most cases of BHD. FLCN
is currently thought to be a tumor suppressor gene. A tumor suppressor
gene's natural role in the body is to make proteins that prevent tumor
formation by limiting cell growth. Research is ongoing to learn more
about BHD.
How is BHD inherited?
Normally, every cell has two copies of each gene: one inherited from
the mother and one inherited from the father. BHD follows an autosomal
dominant inheritance pattern, in which a mutation happens in only one
copy of the gene. This means that a parent with a gene mutation may pass
along a copy of their normal gene or a copy of the gene with the
mutation. Therefore, a child who has a parent with a mutation has a 50%
chance of inheriting that mutation. A brother, sister, or parent of a
person who has a mutation also has a 50% chance of having the same
mutation.
Having the mutation in one copy of the gene is enough to cause BHD.
However, current research shows that a person with BHD must have
mutations in both copies of the FLCN gene in order for a tumor to
appear. A person can be born with one mutated gene (the autosomal
dominant inheritance pattern described above) and then acquire a
mutation to the second copy of the FLCN gene at some point during his or her lifetime. Then, with both copies of the FLCN gene altered, the body loses its ability to suppress tumor growth.
How common is BHD?
BHD is considered to be rare. The number of people and families who
have BHD is unknown. To date, about 60 families worldwide have been
reported to have BHD.
How is BHD diagnosed?
BHD is suspected when a person has skin tumors associated with BHD,
especially if that person or his or her family members have a history of
lung cysts, spontaneous pneumothorax, or kidney cancer.
BHD is also suspected in families with multiple cases of kidney cancer,
particularly if family members have had different types of kidney
cancer. Genetic testing to look for mutations in the FLCN gene is available for people suspected of having BHD.
What are the estimated cancer risks associated with BHD?
BHD is associated with an increased risk for kidney cancer,
particularly the chromophobe renal cell carcinoma (RCC) type of kidney
cancer. The estimated risk for kidney cancer in people with BHD is
around 15%. The risk of kidney cancer is significantly increased in
people who smoke. Individuals with BHD or at risk for BHD should avoid
smoking. It is not known if people with BHD have an increased risk of
other specific types of cancer.
What are the screening options for BHD?
There are no specific screening guidelines for BHD. Due to the risk of
kidney cancer, some doctors suggest that individuals who have BHD or a
family history of BHD have a yearly ultrasound
(which uses sound waves to create a picture of the internal organs) of
their kidneys, beginning at age 25. Other doctors suggest an abdominal
computed tomography (CT or CAT; creates a three-dimensional picture of
the inside of the body) scan or magnetic resonance imaging
(MRI; uses magnetic fields, not x-rays, to produce detailed images of
the body) every two years. Evaluation by a dermatologist (a doctor who
specializes in diseases and conditions of the skin) and screening for
lung cysts are also suggested.
Screening options may change over time as new technologies are
developed and more is learned about BHD. It is important to talk with
your doctor about appropriate screening tests.
Learn more about what to expect when having common tests, procedures, and scans.
Questions to ask the doctor
If you are concerned about your risk for kidney cancer, talk with your doctor. Consider asking the following questions:
- What is my risk of developing kidney cancer?
- What can I do to reduce my risk of cancer?
- What are my options for cancer screening?
If you are concerned about your family history and think your family may have BHD, consider asking the following questions:
- Does my family history increase my risk of developing kidney cancer?
- Are the skin tumors on me or on my family members consistent with a diagnosis of BHD?
- Should I meet with a genetic counselor?
- Should I consider genetic testing?
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