Cystic Fibrosis


Cystic fibrosis is an autosomal recessive trait on chromosome 7. This
disorder affects chloride transport resulting in abnormal mucus production.
This lifelong illness usually gets more severe with age and can affect both
males and females. Symptoms and severity differ from person to person. Cystic
fibrosis is the most common fatal inherited disease among whites and the major
cause of chronic lung disease in children. 50% of people are expected to live
to be 30, but a majority die before age thirteen. 1:2000 whites have cystic
fibrosis, 1:17000 blacks, 1:6000 live births, 1:2500 Americans, and 1:20 is a
carrier.
The genes are inherited in pairs, with one gene coming from each parent
to make the pair. Cystic fibrosis occurs when both genes have mutations. A
person with cystic fibrosis receives one cystic fibrosis gene from each parent.
The parents of a child, with cystic fibrosis, each carry one nonworking copy of
the gene and one working copy of the gene. The parents are called cystic
fibrosis carriers, and because they have one working gene they have no symptoms.
Carrier parents have 1:4 chance to have a child who is a noncarrier of cystic
fibrosis, a 1:2 chance to have a child who carries the gene, and a 1:4 chance
with each pregnancy to have an affected child. If you have a son or daughter
with cystic fibrosis, then you have a 1:1 chance of being a carrier. If you have
a brother or sister with CF, you have a 2:3 chance of being a carrier. If you
have a niece or nephew with CF, you have a 1:2 chance of being a carrier. If
you have an aunt or uncle with CF, you have a 1:3 chance of being a carrier and
a 1:4 chance if you have a 1st cousin with CF.
Cystic fibrosis affects the lungs in particular. The secretions are
thick and sticky rather than thin and watery. This interferes with the removal
of dust and germs. It can lead to lung infections and even chronic lung damage.
Air passages become clogged with mucus and there is often widespread obstruction
of the bronchioles. Expiration is especially difficult. More and more air
becomes trapped in the lungs, which results in obstructive emphysema.
Atelectasis can occur leaving small areas collapsed. Eventually the chest
assumes a barrel shape. The right ventricle, which supplies the lungs, may
become strained and enlarged. Clubbing of the finger and toes may occur due to
the compensation response indicating the chronic lack of oxygen.
Cystic fibrosis affects the pancreas. The mucus clogs the duct and
blocks the transfer of enzymes from the pancreas to the intestines. These
enzymes are needed to break down food that is necessary for proper growth and
weight gain. The mucus in the digestive tract blocks the absorption of
necessary nutrients. This is why there is often no weight gain despite good
appetites. This can be associated with failure to thrive. The buttocks and
thighs atrophy or waste away due to the fat disappearing from main deposit sites.
People usually have light colored stools. There is also decreased blood
cholesterol due to the poor absorption of fats from the intestine.
Cystic fibrosis can also affect the reproductive systems. Men are
usually sterile due to the mucus blockage or absence of the vas deferens. Women
usually have difficult conceiving, because the mucus interferes with the passage
of sperm.
Cystic fibrosis is usually diagnosed in childhood. Mild cases may not
be detected until adulthood. Common symptoms include chronic cough, wheezing,
cyanosis, difficulty breathing, irritability, excessive mucus production, sinus
infections, nasal polyps, recurrent pneumonia, poor growth, frequent loose foul-
smelling stools, enlarged fingertips, and skin that is salty to the taste. The
sweat test is usually used to detect high levels of salt. More than 60m Eq/L of
chloride in sweat up to age 20 is diagnostic of CF when 1 or more criteria are
present. Levels of 40-60 are highly suggestive. Direct genetic testing or
reverse dot-blot can also be used. Amniocentesis is performed between weeks 15-
22. Chorionic villus sampling (CVS) can be used to take a piece of placental
tissue between weeks 9-12. Labs are also used in diagnosing CF. There is
decreased pancreatic enzymes trypsin, lipase, and amylase. Absence of trypsin
alone is indicative of CF.
One complication of CF is a rare condition known as meconium ileus. The
intestine of the newborn becomes obstructed with abnormally thick meconium due
to the absence of pancreatic enzymes. The intestine can rupture resulting in
shock. Signs and symptoms develop within hours after birth and include absence
of stools, vomiting, and abdominal distention.