Hemophilia: One of the better-known rare diseases. Blood of people who carry the disease does not clot properly, as they are missing certain coagulation factors. Hemophilia is exclusively passed on through the X chromosome, which explains why mostly males suffer from it. Females have two X-chromosomes, and one defective gene can be compensated for by the other.

Before effective treatment became available, life expectancy of hemophiliacs was only 11 years. Nowadays, patients have near-normal quality of life and lives about 10 years shorter than males without the disease. The most common form of hemophilia is present in 1 in 5,000 to 10,000 male births.

Amyotrophic lateral sclerosis: ALS or Lou Gehrig's disease affects motor neurons, causing muscle weakness throughout the body. Ultimately, patients cannot control muscle movement. Most die of respiratory failure. Stephen Hawking is a prominent carrier of the disease, but he is a rare case: For most patients, the time span between onset of the disease and death is only about three years. Hawking first showed symptoms 50 years ago. Every year, 1 to 3 in 100,000 people develops ALS.

Alstrom syndrome: Children with this disease are obese early on in life. In addition, they often develop heart problems and - to a certainty of 100 percent - will go blind. In the whole world, around 500 people have the disease. Alstrom Syndrome is heredity and passed on recessively. So far, there is no cure. Life expectancy is low, with most patients dying as young adults.

Tuberous sclerosis: Patients with this disease are lacking certain tumor suppressive proteins. As a consequence, tumors grow in the brain and in vital organs such as the kidney, heart, eyes, lung and skin. The tumors cause developmental delays, and lead to different types of seizures that patients suffer from all their lives. Most cases occur due to spontaneous genetic mutations, but the disease can also be inherited. There is no cure for tuberous sclerosis; however, symptoms can be treated. It occurs in 10 to 16 births for every 100,000.

Mucopolysaccharide diseases: There are seven distinct types of these metabolic disorders, which are caused by absence or malfunctioning of a certain enzyme. Depending on which type of mucopolysaccharide disease they have, patients could suffer from constant pain, impaired motor function, cognitive impairment or severe behavioral problems. They might also display thickened skin, dwarfism or excessive body hair. The disease occurs in 1 in every 50,000 to 280,000 people. There is currently no cure; treatment is directed at improving patients' quality of life.