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Growing Up With Us...
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A Newsletter For Those Who Care For Children
Volume 16, Issue 6
CYSTIC FIBROSIS… THE BASIC DEFECT
June 2010
Editor-in-Chief: Mary Myers Dunlap, MAEd, RN
BEHAVIORAL OBJECTIVES
AFTER
READING THIS NEWSLETTER THE
LEARNER WILL BE ABLE TO:
1.
Discuss the transmission of and the basic defect
associated with CF.
2.
Describe effects of CFTR on the sweat glands,
respiratory and gastrointestinal systems, as well as on
other body organs.
Cystic fibrosis (CF) is a chronic, genetic disorder that
causes dysfunction in the exocrine glands – those that produce
substances, such as mucus, into ducts, rather than into the
blood stream as do endocrine glands. With CF, instead of
producing a thin, free flowing secretion, the mucous glands
produce thick, dehydrated mucous. These secretions clog the
lungs, lead to infection, and block the pancreas, which stops
digestive enzymes from reaching the intestine where they are
required in order to digest food. Other body organs are also
affected.
CF is the most common autosomal recessive disease
among Caucasians, affecting approximately one in 3,200 live
births. The disease is less common in other races and ethnic
groups - one in 11,500 live births among Hispanics, one in
14,000 to 17,000 in African Americans, and one in 25,500 in
Asian Americans.
This newsletter will discuss the transmission and the basic
defect associated with CF. Effects on the sweat glands,
respiratory and gastrointestinal systems, as well as on other
body organs, from CFTR will be described.
One in 31 Americans (more than 10 million people) is a
carrier of the abnormal CF gene. The birth of a child with a
recessive condition, is often a total surprise to the parents,
since in most cases, there is no previous family history of
the condition. Many autosomal recessive conditions occur
this way. It is estimated that all people carry about 20
recessive genes that cause genetic diseases or conditions.
It is only when a person has a child with a partner that
carries the same recessive gene mutation, that there is a
chance of having a child with a recessive disorder.
The Basic Defect: The mutated gene responsible for CF is
located on chromosome seven, along with its protein
product, cystic fibrosis transmembrane conductance
regulator (CFTR), which was first identified in 1989. Healthy
people have normal functioning CFTR, while people with
CF have defective CFTR.
CFTR is responsible for the movement of chloride ions
through the membrane of those cells that produce mucus,
sweat, saliva, tears, and digestive enzymes. The normal
transport of chloride helps control the movement of water in
tissues and the viscosity of fluids within the cells, while
absorption of sodium within the cells controls the volume of
fluid produced. Normally, the chloride ion exits across the
cell membrane, through the CFTR protein channel. The
chloride, which has a negative charge, pulls the positively
charged sodium with it. In CF, because the CFTR is
defective, these ions, as well as water, cannot exit across
the cell. As a result, epithelial cells, those that line hollow
organs and glands and those that make up the outer
surface of the body, such as cells that line the
passageways of the lungs, pancreas, and other organs,
produce mucus and secretions that are unusually thick and
sticky. This mucus clogs the airways and glands, causing
the characteristic signs and symptoms of cystic fibrosis.
CYSTIC FIBROSIS
THE EFFECTS OF CFTR
TRANSMISSION: To have CF, a child must inherit two
abnormal CF genes
from each parent,
identified in the Punnett
square as N n. The
parents have one
abnormal gene, are
asymptomatic, and are
referred to as carriers.
Each time two carriers
have a child, there is a
25% chance the baby
will have CF (n n), a 50% chance the baby will be a carrier
(N n), and a 25% chance the baby will be healthy (NN).
RESPIRATORY: Pulmonary complications are present in
almost all children with CF, but the
extent varies. Although the lungs
are generally normal at birth, most
children develop pulmonary disease
beginning in infancy or early
childhood. The epithelial lining of
the respiratory tract contains both
mucus-secreting goblet cells and ciliated cells. These cells
are bathed in fluid, and a layer of mucus rests on top of the
cilia. In healthy lungs, the ciliated cells beat the mucus layer
that contains inhaled foreign particles and microorganisms
up toward the larger bronchi and trachea, where it is either
expectorated or swallowed.
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In CF, due to CFTR, the fluid and the mucus are thick and
sticky, which inhibits the cilia from propelling it up and out of
the airway. It accumulates and gradually decreases the size
of the bronchioles and bronchi, making the movement of
mucus even more difficult.
Initial symptoms of respiratory disease associated with
CF include wheezing and a dry, nonproductive cough.
Eventually with obstruction of small air passages, dyspnea
occurs, as well as a wet cough with gagging and vomiting.
With disease progression, as gas exchange is significantly
impaired, a barrel-chest deformity, clubbing of the fingers
and toes - the rounding of the ends and swelling of digits,
and cyanosis occur.
Frequent respiratory infections are common in children
with CF. Infants and children normally experience 2 -3
acute illnesses per year. But, with CF the mucous retained
in the lungs serves as an excellent medium for bacterial
growth and respiratory infections are frequent. With CF, the
child’s lungs quickly become colonized with bacteria, and
once the pathogens are established, they become difficult
to eradicate. Repeated episodes of bronchitis and
bronchopneumia are common. The increased frequency of
respiratory tract infections may be suspicious of CF before
a diagnosis is made.
SKIN: Sweat is produced in the coil of the sweat gland.
Normally, as the secretions move
toward the skin surface, the
sodium and chloride are absorbed
back into the bloodstream.
However, in children with CF, the
chloride is not reabsorbed into the
bloodstream, because of the
CFTR defect, nor is the sodium.
This causes the sweat to have a
high concentration of salt. One of the first signs of cystic
fibrosis is an excessively salty taste to the skin. Parents
often can taste the salt when they kiss their child. Children
with CF can quickly become dehydrated if they are not
mindful of the possibility of salt depletion through sweat.
Excessive sweating in hot weather or with fever may lead to
dehydration and circulatory failure.
GASTROINTESTINAL: The pancreas is another organ often
severely affected in CF, occurring in approximately 90% of
children with CF. The abnormal CFTR mechanism results
in obstruction of the pancreatic ducts by thick, sticky mucus.
The pancreas is then unable to produce or secrete
pancreatic enzymes, necessary for digestion. Therefore,
food is not digested properly, particularly fats (including fatsoluble vitamins) and protein, and the body is not able to
absorb nutrients. Therefore, when a child eats fatty food,
the fat passes through the digestive system without getting
broken down or absorbed by the body. It mixes with the
stool as it travels through the intestines, and then is
excreted in its undigested form. This is what causes
steatorrhea, the characteristic frequent, bulky, oily, foulsmelling stools that tend to float on top of the toilet water.
Children with pancreatic insufficiency require oral
pancreatic enzyme supplementation with each meal and
snack. If untreated, pancreatic insufficiency can lead to
numerous problems, including severe malnutrition and
delayed growth. Failure to thrive, due to poor growth and
poor weight gain, is common despite a normal food intake.
In time, the progressive fibrosis of the pancreas also may
destroy the islet cells that are responsible for insulin
secretion. This leads to CF-related diabetes mellitus.
Meconium ileus is the earliest manifestation of CF,
occurring in 10% to 15% of newborns with CF. Rectal
prolapse occurs in 20% of untreated infants and toddlers.
OTHER ORGAN SYSTEMS: Abnormal CFTR functioning can
lead to problems in many other organ systems. Sinus
mucus is thick and sticky, often leading to chronic infection.
There can also be blockage of the bile ducts within the liver,
contributing to fat malabsorption and causing biliary fibrosis
and cirrhosis. More than 95% of males with CF are infertile
because of the bilateral absence of the epididymal ducts
and vas deferens. In women, cervical mucus is thicker than
normal. This impedes sperm migration and makes
pregnancy more difficult.
SCREENING AND DIAGNOSIS:
After much debate, as of 2010, all states have passed
legislation requiring newborns to be screened for cystic
fibrosis (CF). The identification of increased
immunoreactive trypsinogen (IRT) levels in the blood has
made neonatal screening for CF possible. Trypsinogen is
one of the secretory products of the pancreas making its
level in the blood a specific marker of pancreatic function.
Detection of high levels of IRT in the newborn period place
the infant at risk for CF. Newborn screening for CF is not a
diagnostic tool. If the newborn screening result is positive
the sweat test is done at 2-4 weeks of age to rule out or
confirm a CF diagnosis.
The “sweat test”, the
quantitative pilocarpine
iontophoresis sweat test is the
“gold standard” for diagnosing
CF currently, as it has been for
more than 50 years. The sweat
test measures the chloride
content in the child’s sweat. During the test, a colorless,
odorless chemical, that causes sweating, is put on a small
area on an arm or leg. An electrode is then put over that
spot and the technician applies a weak electrical current to
the area to cause sweating. A child may feel tingling in the
area, or a feeling of warmth. The sweat is then collected for
laboratory analysis. Sweat chloride levels of 60 mEq/L or
greater are considered diagnostic for cystic fibrosis. If the
sweat chloride test results fall into the “intermediate” range,
30 - 59 mmol/L in infants 6 months and younger, and 40 59 mmol/L for children over 6 months of age, the sweat test
is usually repeated.
Today, approximately 30,000 people in the United States have
CF. The median age of survival among people with CF has
improved dramatically, from less than two years in 1930 to
almost 38 years today. An upcoming newsletter will discuss
implications for the healthcare provider related to parent
education and support for the child with CF and his/her family.
Growing Up With Us, Inc.
PO Box 481810 • Charlotte, NC • 28269
Phone: (919) 489-1238 Fax: (919) 321-0789
Editor-in-Chief: Mary M. Dunlap MAEd, RN
E-mail: [email protected]
Website: www.growingupwithus.com
GUWU Testing Center
www.growingupwithus.com/quiztaker/
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Page 2 of 4
Name:_____________________________________________________
Date:___________________________________
Employee ID#:____________________________________________
Unit:____________________________________
POPULATION/AGE-SPECIFIC EDUCATION POST TEST
GROWING UP WITH US...
Caring For Children
June 2010
Competency: Demonstrates Age-Specific Competency by correctly answering 9
out of 10 questions related to Cystic Fibrosis… The Basic Defect.
CYSTIC FIBROSIS… THE BASIC DEFECT
Mark, 4 months old, is suspected of having CF.
1. Mark’s newborn screening test was positive. Which of the following is correct concerning newborn
screening CF?
a.
b.
c.
d.
90% of the states in this country require it.
It is diagnostic for CF.
It is performed mainly on high-risk newborns.
Positive results are followed up with a sweat test at 2-4 weeks.
2. All of the following are first signs of CF EXCEPT:
a.
b.
c.
d.
the baby’s skin tastes salty when kissed.
meconium ileus.
respiratory infections.
steatorrhea.
3. In CF, the basic defect is in:
a.
b.
c.
d.
increased trypsinogen.
the CFTR protein channel.
the endocrine glands.
sodium and chloride metabolism.
4. CF is which type of genetic trait?
a.
b.
c.
d.
Mitochrondial
Autosomal dominant
Autosomal recessive
X-linked
5. CF affects all races and ethnic groups equally.
a. True
b. False
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Page 3 of 4
Name:_____________________________________________________
Date:___________________________________
Employee ID#:____________________________________________
Unit:____________________________________
POPULATION/AGE-SPECIFIC EDUCATION POST TEST
GROWING UP WITH US... Caring For Children
CYSTIC FIBROSIS… THE BASIC DEFECT
6. Mark’s mother asks, “How could this have happened? We have no history of cystic fibrosis in our families.
We have another child, Susan, that’s perfectly healthy and so are we.” The healthcare provider
appropriately responds:
a.
b.
c.
d.
“Cystic fibrosis tends to only affect males, so that’s why your daughter doesn’t have it.”
“With cystic fibrosis both parents are carriers for it. I’ll be glad to go over that with you.”
“DNA testing will probably be done to insure your husband is Mark’s father.”
“Since there’s no family history, I’ll have to check with Mark’s doctor.”
7. Mark’s mother says, “We were planning on having four children. So, since Mark has cystic fibrosis that
means our others won’t have it, right?” The healthcare provider responds:
a.
b.
c.
d.
“That’s exactly right. If you have 4 children, 1, or 25%, will have cystic fibrosis.”
“Yes, they won’t have cystic fibrosis, but there’s a 50% chance they’ll be carriers.”
“Your chances are about the same as for anybody else.”
“Your risk for having a child with cystic fibrosis is 25% for each pregnancy.”
8. Mark has a “sweat test” done, which:
a.
b.
c.
d.
measures the sodium content in his sweat.
is diagnostic if the value is 60MEq/L.
is most accurate in infants 6 months of age or younger.
detects IRT.
9. If a child has pancreatic involvement associated with CF, which of the following is NOT characteristic of the
child’s stools?
a.
b.
c.
d.
Bulky
Bloody
Frequent
Foul-smelling
10. Cystic fibrosis often leads to poor weight gain and poor growth.
a. True
b. False
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