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Without doubt, Cystic Fibrosis is one of the most
well known and most studied genetic diseases in modern medicine. Despite the
extensive research surrounding the condition, there is currently no known cure
for the condition and as such, treatment consists simply of alleviating the symptoms
associated with the illness, rather than addressing the underlying pathology of
the respiratory tract and, to a lesser extent, the digestive and reproductive
tracts(1) .Unfortunately, Cystic Fibrosis is extremely common in the British
Isles- more than 10,400 people in the UK suffer from the disease and it is
thought that 1 in 25 of British people carry the faulty gene causing it, usually
unknowingly(2). Meanwhile, Ireland has the highest incidence of cystic fibrosis
in the world, with a whopping 1 in 19 Irish people being a carrier of the
disease (3).

The genetics behind Cystic Fibrosis are well
understood. Cystic Fibrosis is an autosomal recessive inherited disorder,
caused by a mutation of the gene on the long arm (the “q” arm) of chromosome 7
in the region 7q31.2 (4). ‘Autosomal’ refers to the 22 non-sex chromosomes (5)
and ‘recessive’ means that a faulty copy of the gene must be inherited from
both the mother and the father in order for Cystic Fibrosis to be shown in the
person. If a single copy, from either the mother or father only was to be
inherited, the individual would not show any of the diseases’ symptoms. However,
that person would be a carrier of cystic fibrosis and could still pass the
mutation on to their own children in the future. Consequentially, genetic
diseases caused by recessive mutations, as in the case of Cystic Fibrosis, can
lay dormant in families for many generations. If two carriers have children,
the chance that any given child will inherit the genes required for Cystic
Fibrosis follows Mendel’s Laws; these predict
that, in such a scenario, each child has a 25% chance of inheriting cystic
fibrosis and each has a 50% chance of being an asymptomatic carrier of the
disease like his or her parents (6).

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Most commonly, the mutation associated with Cystic
Fibrosis results in the deletion of the 508th amino acid that codes for a
protein called Cystic Fibrosis Transmembrane conductance Regulator (CFTR) (4). In
normal physiology, CFTR acts as a cAMP-dependent chloride ion channel pump in
airway epithelia cells. However, in Cystic Fibrosis, The genetic mutation means
that the body’s epithelial cells can’t pump chloride ions (Cl-) out of the cell
and into the lumens of the various tracts of the body. As a result, less water
is secreted from cells and viscous mucus is produced by the body (7). In the
respiratory tract, the thick mucus builds up on the inner lining of the lungs.
White blood cells can become trapped in this mucus, rupture and make the mucus
even more viscous (6). As a consequence of the thick mucus, people with Cystic
Fibrosis often experience wheezing, breathlessness and a persistent cough, as
their body attempts to remove the accumulated excess mucus. Furthermore, people
who suffer from Cystic Fibrosis also have an increased risk of contracting
chronic infections, as the thick mucus provides an ideal environment for
bacteria and fungi to proliferate. In the digestive system, the mucus produced
prevents digestive enzymes from the pancreas reaching the small intestine. This
is problematic as these digestive enzymes are responsible for the degradation
of proteins. Bile salts are also often blocked on their way from the pancreas
to the intestine as well, so the digestion of fats is often also incomplete. This
can result in nutritional deficiencies, as the body will be unable to absorb
proteins, fats and fat-soluble vitamins. Digestive symptoms of Cystic Fibrosis
include the production of pungent, greasy stools, lack of weight gain and
growth, intestinal blockage, (in new borns called ‘meconium ileus’) and severe
constipation. Finally, the vast majority of men who suffer from cystic Fibrosis
are infertile. This is due to either the blockage of the vas deferens (the tube
which connects the testes and prostate gland) due to mucus build up, or the
fact that the vas deferens is completely missing. On the other hand, women with
cystic fibrosis, while most often less fertile than other women, can still conceive
and may have successful pregnancies. Despite this, however, pregnancy is prone
to worsen the symptoms of cystic fibrosis. (8)

Receiving a diagnosis of cystic fibrosis has lasting
consequences for an affected individual, their family, and any potential
spouse. In most cases, a child who has the typical indicative clinical symptoms
or a family history and positive sweat tests will confirm suspicions of cystic
fibrosis. The diagnostic criteria are based on phenotypic evidence and have
been useful in guiding clinical practice since the early 1960s (9). Since 2003
in Scotland and 2007 in the rest of the UK, all new born babies can be tested
for cystic fibrosis via the ‘heel prick test’. (10) When a baby is five to
eight days old, their heel is pricked to collect a sample of four drops of
blood. The test is not specific to cystic fibrosis, and in fact tests for nine
rare but serious conditions. It is also worth noting that a positive heel prick
test does not necessarily mean that a child has cystic fibrosis -as a result,
confirmation tests are needed. This may include a sweat test or a genetic test.
(11) If a sweat test is conducted, and a sodium concentration of over 60 mmol/L
is discovered it is likely that a patient has Cystic Fibrosis.  Finally, other factors which may lead to a
diagnosis include radiological features of bronchiectasis, the absence of vas
deferens and epididymis and raised blood immunoreactivity trypsin levels. (4)

In conclusion, Cystic
Fibrosis is one of the most debilitating conditions which modern society faces.
Thankfully, the future looks bright for those with Cystic Fibrosis as more
complex gene therapies are currently being developed which may put an end to
this life changing disease. Nevertheless, there remains much more study to be
done with regards to the pathological basis of the body systems and further
developments in the field may unlock the secret to curing one of the worst
diseases known to mankind.

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