Cystinosis – causes, symptoms, diagnosis, treatment, pathology


With cystinosis, “cystin-” refers to cystine,
an amino acid, and “-osis” implies disease. So, cystinosis is a rare condition caused
by mutations of the CTNS gene that leads to a cystine buildup in the body. especially
the kidneys and eyes. This can cause tissue damage, especially in the kidneys and eyes. Cystine is an amino acid that comes from our
diet. When food travels through the stomach and intestines, the proteins within, are broken
down into tiny fragments, called oligopeptides, or small strings of amino acids. Turnover
of muscle, bone and other parts of the body provide another source of protein that can
be broken down into oligopeptides. Many of these oligopeptides end up in specialized
vesicles, called lysosomes, found inside all of our cells. called lysosomes all over our
bodies. Here, they are further broken up into amino acids like cystine. Now, cystine, like
any other amino acid has to leave the lysosome, and it does this with the help of a specific
protein. Generally, genes tell our bodies how to make proteins. So, the CTNS gene encodes
for the protein cystinosin, a transporter that is found embedded in the lysosomal membrane.
Its function is to export cystine out of the lysosome. Now, in cystinosis, any one of over 100 mutations
can affect the CTNS gene, leading to a defective cystine transporter. Without a working transporter,
cystine has no way of leaving the lysosome, so it accumulates, turning into cystine crystals
in the process. Crystals that slowly damage organs like the kidneys and eyes. The mutations that cause cystinosis are inherited
in an autosomal recessive fashion, so two people have to be at least carriers of the
mutated CTNS gene, to pass on the condition. There is a 25% chance that both people will
pass down their own CTNS mutation to the offspring. Only when two mutated CTNS genes are passed
is the condition usually expressed. In general, humans have two copies of their
genes, so both must be damaged for there to be so little cystine transport that cystinosis
occurs. That means that a person with cystinosis must receive a mutated CTNS gene from both
the mother and father. For each such mating, there is a 25% chance that both parents will
pass down their own CTNS mutation to the offspring. Now, depending on the CTNS gene mutation,
three types of cystinosis can develop that differ in the age of onset and severity of
symptoms. They are nephropathic, or infantile, late onset, and ocular. Nephropathic, or infantile
cystinosis, is the most common and most severe form of cystinosis. In this disease, the kidneys
are affected, and the infants develop Fanconi syndrome, a condition, where minerals and
nutrients are not absorbed, but instead, are excreted in the urine. So, some of the symptoms
are linked to the kidneys like excessive thirst, excessive urination, electrolyte imbalances,
vomiting, and dehydration with or without fever. Other symptoms include the failure
to thrive, cystine crystals in the cornea, and elevated cystine levels in white blood
cells. There’s also late onset, adolescent, or intermediate cystinosis where the symptoms
of nephropathic cystinosis appear later in life, around 8 to 20 years of age. Lastly,
ocular cystinosis, it usually affects adults during middle age. Here, the eyes are affected,
and the kidneys are spared. Without treatment, people eventually develop photophobia due
to cystine crystal accumulation in the eyes. We are coming to realize that there is a spectrum
of severity in cystinosis and the 3 subtypes can be difficult to differentiate. A diagnosis of cystinosis is based upon identification
of characteristic symptoms, a detailed patient history, a thorough clinical evaluation and
a variety of specialized tests. The specialized test includes measuring cystine levels in
certain white blood cells, and molecular genetic testing. The treatment of cystinosis is directed toward
the specific symptoms that are apparent in each person. But overall, cysteamine, a cystine-depleting
agent, is the first-line treatment for cystinosis. All right, as a quick recap, cystinosis is
a rare condition caused by mutations of the CTNS gene that leads to a cystine buildup
in the body, especially causing damage to organs like the kidneys and eyes. The CTNS
gene encodes for the protein cystinosin, a transporter that is found embedded in the
lysosomal membrane. Its function is to export cystine out of the lysosome. Three types of
cystinosis can develop; nephropathic, or infantile, late onset, and ocular. Nephropathic cystinosis
is the most common and severe, and ocular cystinosis only affects the eyes. It’s diagnosed
with specialized tests like measuring cystine levels in certain white blood cells, and molecular
genetic testing. And it’s treated with cysteamine, a cystine-depleting agent.

9 thoughts on “Cystinosis – causes, symptoms, diagnosis, treatment, pathology”

  1. Did you plan to release this video the same day the channel “Dory Story” released the video “I Cry Diamond Tears?” It seems to be quite a coincidence that two videos about cystinosis would be released on the same day.

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