Rare diseases, also known as orphan diseases, refer to a diverse group of medical conditions that can affect various organ systems and have wide-ranging impacts on individuals’ physical and mental well-being. They often require complex, multidisciplinary care as they are usually life-threatening and debilitating.

Unlike common diseases, a rare disease affects a relatively small number of individuals. The definition of rare diseases in Canada, as in many countries, is based on prevalence. Since Canada does not have a standard definition for rare diseases, the European definition is commonly used, which states that a disease is considered rare if it affects fewer than 1 in 2,000 individuals. 

Estimating the exact number of rare diseases is challenging due to various factors, including the evolving nature of medical research and the discovery of new conditions. However, it is estimated that there are as many as 7,000 – 10,000 recognized rare diseases, of which many are genetic (~80%) and start in childhood. More than one-third of these diseases remain unsolved, meaning that their genetic cause is unknown. Some rare diseases are well-documented and thoroughly studied, while others are extremely rare, with only a handful of cases reported worldwide.

The exact number of people affected by rare diseases is challenging to pinpoint due to the vast number of distinct rare diseases, varying prevalence rates, and differences in reporting and identification. While each rare disease may be uncommon individually, collectively they are estimated to affect over 300 million people worldwide and approximately 1 in 12 individuals in Canada, two-thirds of them children. It is important to note that these figures are general estimates and may not capture the full scope of rare diseases, given their diversity and the dynamic nature of diagnostic capabilities and awareness.

Rare diseases span the entire medical spectrum, encompassing a diverse range of conditions. While some, like cystic fibrosis, are widely known, others, such as cat eye syndrome, may be less familiar. Notably, most types of cancer fall under the category of rare diseases, with only a few exceptions. These conditions can manifest in various forms, affecting neurological and neuromuscular systems, metabolism, chromosomes, skin, bones, and various organs and systems throughout the body, including the heart, blood, lungs, kidneys, and more. The world of rare diseases is extensive and covers a multitude of medical areas.

Individuals living with a rare disease and their families face a multitude of challenges that are common across diseases and countries. Some common challenges include:

• Delayed diagnosis: Many rare diseases are difficult to diagnose, leading to delays in receiving appropriate medical care. Misdiagnoses and a lack of awareness among healthcare professionals contribute to the diagnostic odyssey experienced by patients.
• Limited treatment options: The rarity of these diseases often means that there are limited treatment options available. Research and development of therapies for rare diseases may be neglected due to the small patient populations.
• Isolation and lack of support: Patients with rare diseases often feel isolated because these conditions are not well-known. Support networks may be limited, and patients may struggle to find others who understand their experiences.
• Emotional and psychological impact: Dealing with a rare disease can take a toll on the mental health of patients and their families. Coping with uncertainty, managing chronic symptoms, and navigating the healthcare system can contribute to stress and anxiety.
• Financial burden: Rare diseases can impose a significant financial burden on individuals and their families. Expenses may include costs for specialized medical care, medications, and sometimes travel for expert consultations.
• Lack of research and clinical trials: Limited research on rare diseases means that there may be a lack of understanding of the underlying mechanisms and optimal treatment strategies. Additionally, the small patient populations make it challenging to conduct clinical trials.
• Healthcare system navigation: Navigating the healthcare system can be challenging for individuals with rare diseases. Coordinating care among various specialists and accessing appropriate resources may require considerable effort.

There are different resources available that provide information on specific rare diseases. Among them, the following are good places to start:

• The Genetic and Rare Diseases Information Center (GARD) provides comprehensive information about rare and genetic diseases.
• Orphanet is a rare disease database that provides information on specific rare diseases and links to patient organizations and expert medical centers.