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About Cystinosis
Nephropathic Cystinosis is an ultra-orphan disease with incidence of 1 per 100,000-200,000 live births. It is an autosomal recessive disorder and belongs to the group of metabolic diseases called lysosomal storage disorders.
The Disease
If Cystinosis is left untreated, cystine crystals accumulate in the lysosomes of all calls leading to permanent organ damage, kidney failure and potentially death by ten years of age.
1National Organisation for Rare Disorders 2021, Cystinosis, National Organisation for Rare Disorders, viewed 13th January 2021, https://rarediseases.org/rare-diseases/cystinosis/
Cystinosis
Rare Disease Caused by mutations of the CTNS gene which leads to Cystine build-up in the body which leads to Tissue damage esp. in the kidneys and eyes.
CTNS Gene
CTNS Gene encodes for the protein Cystinosin, a transporter that is embedded in the lysosomal membrane. Its function is to export cystine out of the lysosome.
Defective Cystine Transporter
In Cystinosis, any one of >100 mutations can affect the CTNS gene which leads to defective cystine transporter. If the cystine transporter does not work, cystine can not leave the lysosome. So it accumulates, turning into cystine crystals in the process. These cystine crystals slowly damage organs e.g. kidneys and eyes.
CTNS Gene Mutation
Humans have two copies of their genes so both must be damaged so that cystinosis occurs. Therefore, a person with Cystinosis must receive a mutated CTNS gene from both the mother and father.
There is a 25% chance that both parents will pass down their own CTNS mutation to the offspring.
Types of Cystinosis
There are 3 types of Cystinosis:
- Nephropathic (Infantile) Most common and severe form Infants develop Fanconi Syndrome (Nutrients and minerals not absorbed and excreted in urine).
- Late Onset
- Occular – only affects eyes
Symptoms
Linked to Kidneys
- Excess thirst
- Electrolyte imbalances
- Vomiting
- Dehydration with/without fever
Other
- Failure to thrive
- Cystine crystals in the cornea
- Elevated cystine levels in the White Blood Cells
Diagnosis
- Identification of characteristic symptoms
- Patient history
- Clinical evaluation
- Specialised tests White Blood Cell cystine
- Molecular genetic testing
Current Treatments
- Directed towards specific symptoms
- Cysteamine – cystine depleting agent
Disadvantages of Current Treatments
- Pill burden – large numbers of capsules are required for each dose.
- Very frequent dosing regime for one of the available treatments.
- Gastro-intestinal side effects e.g. nausea, vomiting, abdominal pain, bad breath and body odour.3,4
3 Cystagon SmPC 2021, Recordati Rare Diseases UK Ltd. EMC – Electronic Medicines Compendium, viewed 13th January 2021. https://www.medicines.org.uk/emc/product/6237/smpc
4 Procysbi SmPC 2021, Chiesi Ltd. EMC – Electronic Medicines Compendium, viewed 13th January 2021. https://www.medicines.org.uk/emc/product/2079/smpc
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