What is Rare Disease?
A rare disease, also referred to as an orphan disease, is any disease that affects a small percentage of the population (ranging from 1 in 1,500 to 2,000 individuals in Singapore context). Most rare diseases are genetic, and thus are present throughout the person’s entire life, even if symptoms do not immediately appear. Many rare diseases appear early in life, and about 30 percent of children with rare diseases will die before reaching their fifth birthday.
Rare diseases are long-standing, life threatening, progressively disabling conditions that affect a small percentage of population and require multi-disciplinary care. One rare disease may affect only a handful of patients in one demographic (eg. In the EU) and another might affect as many as 50,000 in other region (eg. Asia).
Relatively common symptoms can hide underlying rare diseases leading to misdiagnosis and delaying treatment. Quintessentially disabling, the patient’s quality of life is affected by the lack or loss of autonomy due to the chronic, progressive, degenerative, and frequently life-threatening aspects of the disease.
Although rare and genetic diseases, and many times the symptoms, are uncommon to most doctors, rare diseases as a whole represent a large medical challenge. Combine this with the lack of financial or market incentives to treat or cure rare diseases, and you have a serious public health problem.
Rare diseases do not recognize race, colour, nationality or social standing…. they could happen to anyone.
Here are a few statistics and facts to illustrate the breadth of the rare disease problem worldwide.
- There are approximately 7,000 different types of rare diseases and disorders, with more being discovered each day.
- Rare diseases are characterised by a broad diversity of disorders and symptoms that vary not only from disease to disease but also from patient to patient suffering from the same disease.
- 80% of rare diseases have identified genetic origins whilst others are the result of infections (bacterial or viral), allergies and environmental causes, or are degenerative and proliferative.
- 30%, of children won’t live beyond their fifth birthday.
- Rare diseases are responsible for 35% of deaths in the first year of life.
- 95% of rare diseases lack an FDA (USA) approved treatment.
- 8 years is an average time for rare disease patients to receive an accurate diagnosis.
- 350 millions people suffers from rare diseases globally.
- Rare diseases impact more people than Cancer and AIDS combined.
- 50% of rare diseases do not have a disease specific foundation or research support group.
What is Genetic Disease?
While many common diseases (such as heart disease, high blood pressure, types of cancer) have some genetic (that is, inherited) components, genetic diseases are those caused by specific, identifiable elements of a person’s genetic makeup.
A change in the genetic code can occur during the formation of the egg or sperm, or during or soon after conception. In some cases, genetic changes can be inherited from a parent who carried the defective gene, but is clinically healthy.
Genetic diseases can present at any age, infancy, childhood or adulthood. It can cause common problems, for example, developmental delay and poor growth. It can also have rarer presentations such as heart or liver failure.
Many advances have been made in looking for a cure for genetic disease including gene therapy and bone marrow transplantation. However, for most cases, there is no cure. Even so, many patients with genetic diseases can lead fulfilling lives with proper management of their symptoms.
Autosomal recessive genetic diseases
When both parents carry the same recessive gene, there is a 25% chance that the child will inherit the trait from both parents and have the disease, a 50% chance that the pregnancy will inherit the trait from only one parent, or a 25% chance that the pregnancy will not inherit the trait from either parent. An example of autosomal recessive disease is Pompe disease that occurs 1 in 40,000 live births.
Dominant genetic diseases
They are caused by a mutation in one copy of a gene. If a parent has a dominant genetic disease, then each child has a 50% chance of inheriting the disease. An example of a dominant genetic disease is Achondroplasia that occurs in 1 in 25,000 live births.
Sex-linked genetic diseases
They affect males and females differently. This is a smaller set of diseases related to gene mutations on the X or Y chromosomes. One rare disease linked to X chromosome is Fabry disease.
They can occur in any pregnancy. Sometimes these risks are related to the parent’s age and involve extra or missing chromosomes. A second type of chromosome abnormality is a change in the structure or organisation of the chromosomes.
These occur due to many complex interactions and combinations of maternal, environmental and genetic influences. In most cases predictive genetic testing is not available for multi-factoral traits, however a family history assessment may provide more accurate recurrence risks.