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). 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, progressive, disabling conditions that require multidisciplinary care. However, the lack of understanding of these diseases makes these children at risk for serious consequences due to delay in, and sometimes, incorrect diagnosis.
Rare diseases do not recognize race, colour, nationality or social standing…. they could happen to anyone.
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.