(Table of Contents- Lesson 2)
(Next) (Glossary)
(Segments of this section were adapted from the article "The Genetic Family History in Primary Care" by Robin Bennett which was published in Genetics Northwest, Volume 10, Number 2 & 3, December 1995. It is reprinted, with changes, with the permission of the Pacific Northwest Regional Genetics Group)
Many health care providers inquire about family illnesses as part
of the medical evaluation process; however, this information is
often written out in narrative form and may be difficult to interpret.
For example, the statement "Linda's grandmother and two aunts
died of breast cancer" does not indicate whether it was her
maternal or paternal grandmother who had the cancer. Nor does
it indicate how these aunts are related to Linda's mother or father.
Are the affected aunts sisters? Are they biologically related
to Linda's grandmother who had cancer or did they marry into Linda's
biologic family? The exact relationship of these affected relatives
to Linda can make a significant difference when assessing Linda's
need to be referred for genetic counseling.
For these reasons it is logical to consider drawing a pedigree
when asking about family illnesses. The construction of a pedigree
provides a graphic record of the family health history. It can
be viewed at a glance and is easily annotated and updated. Relationships
of family members are represented schematically and may demonstrate
patterns of transmission of familial disorders. Figure 2.1 shows
the common symbols that are used in pedigree construction and
Figure 2.2 is a sample pedigree with typical notations.
Fig. 2.1. Pedigree symbols
Fig. 2.2. Sample pedigree
The process of taking a pedigree also provides an excellent opportunity
to establish rapport with your patients or their parents. As the
pedigree emerges so will the family relationships such as divorces,
adoptions, estrangements and deaths. This information may alert
you to sensitive issues that might be of concern to your patients
or their families.
Typically, a three-generation pedigree is obtained, beginning
with the patient. For example, if an infant is being evaluated,
the pedigree should include sibs, parents, aunts and uncles, nieces
and nephews and grandparents. When evaluating an adult, it is
often helpful to expand the pedigree to include children and grandchildren.
If a pattern of illness emerges, it is important to extend the
family history back as many generations as possible to include
any additional affected relatives.
THE PROCESS
Before you begin collecting family history information it is helpful
to let your patient or the parents know why you need this information
and how you plan to use it. If people know that this information
is essential to determine the cause of their child's problem or
the risk to an unborn baby, they may be more forthcoming when
asked to answer a series of rather personal questions.
Once you have obtained permission to collect family history information,
begin with your patient. Draw your patient's symbol on the pedigree
form (a circle for a female and a square for a male), and record
your patient's name, date of birth, and relevant health information.
Next, ask for the names and birth dates of your patient's brothers
and sisters and record them on the same generation line in order,
from oldest to youngest. Then inquire about each sib's relationship
to your patient. Determine whether they are full sibs, half sibs
or stepsibs. Find out if any of the sibs have problems similar
to those observed in your patient. Ask specifically about abortions
(both spontaneous and therapeutic), stillbirths and infant deaths
within the sibship, as this type of information may not be readily
volunteered and may be helpful in deciding whether to refer a
family for genetic services.
Once you have collected information about your patient's sibs,
request information about your patient's mother; specifically
her name (both married and maiden), date or year of birth and
relevant health history. For example, if you are concerned about
your patient's short stature, parental heights should be recorded
on the pedigree. If you are working with a person who has a degenerative
neurologic disease like Huntington disease, you should record
age and cause of death. By convention, this information should
be placed on the next generation line up, and maternal ancestors
are noted on the right side of the pedigree form.
Next, inquire about your patient's mother's sibs in order from
oldest to youngest, again recording their names, birth dates and
health histories. Ask about their children and document which
aunts, uncles and cousins have a similar affliction. Also record
any history of infertility or pregnancy loss.
Complete this portion of the pedigree by recording information
about your patient's maternal grandparents on the next generation
line up. If any relatives are deceased, record their ages and
cause of death. Also make note of any other relatives with a health
history similar to the index patient.
You should then repeat this process, asking questions about your
patient's father and his family. Even if there is an obvious pattern
of health problems on the patient's mother's side of the family,
it is prudent to record details on both sides of the family, as
unexpected findings or additional genetic concerns may be discovered.
This practice can also help reduce feelings of blame or guilt.
By convention, paternal information is recorded on the left side
of the pedigree form.
It is important to keep the generation lines clearly defined so
that the grandparents are on the top line, the parents, aunts
and uncles are on the next line, the children, nieces and nephews
(first cousins) are on the next line, etc. The generation lines
should be numbered from top to bottom with Roman numerals I, II,
III, etc. The individuals on each generation line should be numbered
1, 2, 3, etc. from left to right.
If it is not immediately apparent, you should ask if your patient's
parents are related. A history of consanguinity supports the diagnostic
impression of an autosomal recessive single gene disorder. It
affects the recurrence risk for multifactorial conditions and
may alert you to the underlying cause of guilt or other problems
you may have observed when working with a family. It also tells
your patients or their parents that this information is important
to the evaluation process, a fact which may be important if they
are reluctant to share with you that the child's biologic father
may be a relative.
Traditionally, ethnic background is recorded to identify individuals
or couples at risk for certain genetic conditions. African Americans,
for instance, are more likely to carry the gene for sickle cell
disease. One in 30 individuals of Ashkenazi Jewish descent carry
the gene for Tay-Sachs disease. If a person is found to be a member
of a high-risk group, referral should be made for genetic counseling
and carrier testing.
The personal nature of the information recorded on a pedigree
raises several issues surrounding the protection of privacy and
confidentiality. For example, recording a pregnancy termination
may be useful when evaluating a woman with a history of infertility
since it documents that she was able to conceive. However, her
current partner may be unaware of this information. Similarly,
documenting cases of non-paternity, pregnancies conceived by means
of assisted reproductive technology, suicide, alcoholism or deaths
due to HIV may be helpful in establishing or excluding a diagnosis.
However, if released, this information may cause harm to the persons
involved. Therefore, patient confidentiality should be carefully
weighed when choosing which information to record on a pedigree.
Awareness of cultural heritage may be important when taking a
pedigree. For instance, you may find a Native American patient
hesitant to provide "derogatory" information about a
relative (e.g., drinking or drug use, academic behavioral problems),
as doing so could aggravate the situation. Explaining the importance
of the pedigree information for diagnosis usually results in compliance.
Knowledge of the belief system of ethnic groups is important in
genetic counseling.
Record the date when the pedigree was drawn and check this date
each time the patient is seen. Updating the pedigree every year
may uncover emerging patterns. Over time your patients may also
be willing to correct any misinformation they might have shared
with you (e.g., the biologic father of a child, etc.) as the level
of trust is established.
Factual and health information to include in a pedigree: