Welcome to the Rare Classroom, a new series from Patient Worthy. Rare Classroom is designed for the curious reader who wants to get informed on some of the rarest, most mysterious diseases and conditions. There are thousands of rare diseases out there, but only a very small number of them have viable treatments and regularly make the news. This series is an opportunity to learn the basics about some of the diseases that almost no one hears much about or that we otherwise haven’t been able to report on very often.

Eyes front and ears open. Class is now in session.

The disease that we will be learning about today is:

Cystinosis

What is Cystinosis?

• Cystinosis is a form of lysosomal storage disease in which the amino acid cystine accumulates abnormally in the body
  • This genetic disorder causes cystine to build up in the lysosomes, a critical cellular organelle
  • This eventually leads to the buildup of intracellular crystals
• Cystinosis is the most common cause of Fanconi syndrome, in which the cells of the renal tubules are impaired, leading to excessive urination, low levels of phosphorus and potassium, and abnormal carbs and amino acids in the urine
• The disease leads to tissue damage, but the mechanism of this damage isn’t well understood
• There are three different forms of cystinosis
  • Nephropathic cystinosis
  • Ocular cystinosis
  • Intermediate cystinosis

How Do You Get It?

• Cystinosis is linked to a mutation affecting the CTNS gene
  • The gene is located on chromosome 17 and codes for cystinosin, a lysosomal cystine transporter
• The disorder is inherited in an autosomal recessive pattern, meaning that a copy of the mutated gene must be inherited from both parents
• Incidence rate is estimated at 1 in 100,000 to 1 in 200,000 births
  • Interestingly, incidence is higher in Brittany, France at about 1 in 26,000
• Only around 2,000 patients with cystinosis have been recognized

What Are The Symptoms?

• A number of symptoms are associated with cystinosis:
  • Poor growth in newborns
  • Kidney issues, including Fanconi syndrome
  • Rickets
  • Excessive thirst and urination
  • Dehydration
  • Acidic blood
  • Cystine crystals, which usually appear in the cornea by age two
  • Kidney failure may appear by age ten without treatment; sometimes later
  • Photophobia
  • Thyroid problems
  • Blindness
  • Muscle deterioration
  • Diabetes
  • Impaired sweating
  • Impaired swallowing
• These symptoms appear soon after birth in nephropathic disease, but appear later in intermediate cystinosis, around age 12-15
• In ocular disease, many of the more serious symptoms are not present. The primary symptom is photophobia due to cystine crystal build up.

How Is It Treated?

• The primary treatment for cystinosis is cysteamine
  • This is usually available as eye drops or capsules
• Other treatments include sodium citrate, to treat blood acidosis
• Supplements for potassium and phosphorus, as well as some others, are also used
• If kidney failure appears, dialysis or kidney transplant may be needed

Where Can I Learn More???

• Check out our cornerstone on this disease here.
• Learn more about this condition from the Cystinosis Research Network and Next Generation Cystinosis.