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10 Rare Diseases and Prescription Drugs


Carbaglu is used to treat patients with urea cycle disorders (UCDs). Carbaglu specifically addresses N-acetylglutamate synthetase (NAGS) deficiency. Carbaglu is the only drug approved by the FDA for treating high ammonia levels caused by NAGS deficiency in patients of all ages.

While every type of UCD is rare, cases caused by NAGS deficiency are the rarest of them all. Because NAGS deficiency is under-diagnosed, the actual number of individuals affected by this type of UCD remains unknown.


Ravicti is used to treat urea cycle disorders (UCD), genetic diseases that prevent the body from getting rid of ammonia. Urea cycle disorder resulting buildup of the toxic substance can lead to brain damage and death, so forgoing treatment is not an option.

There are an estimated 2,000 individuals in the U.S. who suffer from urea cycle disorders that could potentially be treated by Ravicti. Horizon’s drug treats seven types of UCDs, though it’s unknown whether Ravicti is safe and effective for treating an especially rare type known as N-acetylglutamate synthetase (NAGS) deficiency.


Acthar is prescribed to treat infantile spasms or seizures. This condition typically affects children between the ages of 4 and 11 months old. Acthar is also used to treat a variety of conditions in adults, including multiple sclerosis.

Read: Drug Overdose Deaths, Propel Rise in Mortality Rates (1999-2014)

HP Acthar gel, a drug that’s used to treat multiple sclerosis, infantile spasms, rheumatoid arthritis and a few other conditions. Myozyme is a treatment for Pompe, a rare and sometimes fatal disease that attacks the heart and skeletal muscles.

10 Rare Diseases and Drugs - Most Costly Medical Treatments
Rare Diseases and Drugs – Most Costly Medical Treatments

When it affects infants, mortality often strikes in the first year. Myozyme is a lysosomal glycogen-specific enzyme that in studies increased survivability and reduced patients reliance on ventilators.


The newest of the seven most expensive prescription drugs in the world is spinal muscular atrophy (SMA) drug Spinraza. It’s a fatal genetic disease affecting muscle strength and movement. Patients with spinal muscular atrophy, a savage disease that, in its most severe form, kills infants before they turn 2.

Biogen received FDA approval for the drug, which was initially developed by Ionis Pharmaceuticals in December 2016.


Soliris is the world’s single most expensive drug used to treat two rare diseases atypical hemolytic uremic syndrome (aHUS) and paroxysmal nocturnal hemoglobinuria (PNH). These rare diseases affecting 8,000-10,000 peoples in the world. aHUS affects the body’s immune system in ways that can lead to serious complications, including blood clots.

There are only 1,500 known patients diagnosed with the disease. PNH destroys red blood cells (RBCs), causing patients to have infections, anemia, and blood clots. Since Alexion started selling Soliris two years ago, its stock price is up 130%.

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