Rare diseases are diseases that affect fewer than one in 2,000 people worldwide. While each rare disease affects a limited number of individuals, there are still a lot of them. There are between 5,000 and 8,000 rare diseases.
About 80% of rare diseases are genetic, that is, they are caused by a change in a gene. A genetic disease can be passed on the parents or appear by chance in a person.
Other rare diseases have different causes:
autoimmune diseases, when a person’s own immune system attacks the body’s cells, for example, systemic lupus erythematosus, scleroderma or Sjögren’s disease
infectious diseases caused by a virus, bacterium or parasite, for example, Q fever, botulism or Powassan virus disease
toxic diseases, when they are due to poisoning or a toxic source, for example, lead poisoning or mercury poisoning
isolated rare defects, for example, Goldenhar syndrome, agenesis of the corpus callosum or cleft palate
rare cancers, for example, Ewing sarcoma, neuroendocrine tumours (pheochromocytoma‑paraganglioma) or childhood eye cancer (retinoblastoma)
Who can be affected by a rare disease
Anyone could be born with or develop a rare disease. Rare diseases can affect people of all ages, including children, adolescents and adults. A rare disease can occur at different times in life, depending on the disease and its cause.
About 50% to 75% of people with rare diseases are children. Some of these diseases can be diagnosed at birth through blood screening in newborns.
Rare diseases are thought to affect up to 8% of the Québec population, or about 700,000 people.
Living with a rare disease
Rare diseases can cause discomfort, be debilitating and even be fatal. They can cause chronic pain, affect one or more organs or lead to different forms of deficiency for the affected person.
Some rare diseases can progress over time and cause health to deteriorate, while others remain stable. Early detection and treatment can, in some cases, slow the progression of the disease, or even prevent symptoms from appearing. Depending on the disease, the treatment options are different.
For some diseases, there are treatments that target the cause of the disease and which can greatly improve the health and quality of life of people who have the disease.
However, for many rare diseases, there are few or no targeted treatments. They are referred to as orphan diseases.
In these cases, treatment may be offered to relieve pain or prevent complications, even if no targeted therapy is available. Physical therapy, such as rehabilitation, can also provide support and improve quality of life for some people. Other people are offered palliative care.
Diagnosing a rare disease
Rare diseases are often not well known. So they are sometimes hard to diagnose and manage. Often, specialized or even highly specialized doctors must be involved in order to make a diagnosis and begin management. Indeed, it is normal that not all health professionals are familiar with all the rare diseases that exist.
Difficulty identifying a rare disease can cause delays before a diagnosis is confirmed. This is called the diagnostic odyssey. When it takes too long, it can delay management and reduce the chances of limiting the progression of the disease when treatment is available.
People who need investigation and management for a rare disease must be referred to a specialized clinic by a family doctor or specialized nurse practitioner. They will be able to discuss tests and examinations to diagnose the disease, treatments and management with a health professional.
In Québec, there are more than 500 specialized clinics for a rare disease or a group of rare diseases and even more doctors and professionals who are experts in this field. Most of these clinics are located in interdisciplinary referral centres for rare disease research and treatment.
The Réseau national de navigation clinique en maladies rares (Navi‑Nat) supports health professionals in referring people who do not have a diagnosis, but who are suspected of having a rare disease, to the appropriate specialized clinic. This helps shorten the diagnostic odyssey.
Interdisciplinary referral centres for rare disease research and treatment
At this time, Québec has six interdisciplinary referral centres for rare disease research and treatment. Each centre has a wide range of expertise in rare diseases:
the Centre hospitalier universitaire (CHU) de Québec – Université Laval
the Centre intégré universitaire de santé et de services sociaux (CIUSSS) de l’Estrie – Centre hospitalier universitaire de Sherbrooke
the CIUSSS du Saguenay–Lac‑Saint‑Jean (regional referral centre)
the Centre hospitalier de l’Université de Montréal (CHUM)
the Centre hospitalier universitaire Sainte‑Justine (CHU Sainte‑Justine)
McGill University Health Centre (MUHC)
Early detection of rare diseases
In addition to the many tests and examinations that health professionals can do to diagnose rare diseases, there are a number of programs in Québec to detect certain rare diseases early and manage them quickly:
blood screening in newborns is done to detect certain rare diseases that may be present at birth so that they can be treated as early as possible
preimplantation genetic testing is used to detect the presence of an hereditary disease in embryos resulting from in vitro fertilization before they are implanted in the uterus