This site is an educational service brought to you by BioMarin. No gene therapies for haemophilia A or B have been approved for use or determined to be safe or effective.

What causes
genetic conditions?

Did you know there are approximately 20,000 genes in the human genome? A mutation, or permanent variation, in just one gene can lead to a genetic condition. Knowing what causes a genetic condition is the first step in understanding how, potentially through ongoing research in gene therapy, physicians might be able to treat these conditions differently.

GENETIC CONDITIONS ARE THE RESULT OF MUTATIONS

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Genetic conditions are the result of mutations, or variations, in the structure of a gene. These mutations are most often passed down from biological parents, but can sometimes happen spontaneously. Cystic fibrosis and haemophilia are examples of genetic conditions.

In haemophilia A, the gene responsible for producing factor VIII is mutated. This gene is located in the X chromosome. Males have only one X chromosome, which means that one copy of the mutated gene is enough to cause haemophilia, making it more common in this population.

While it is rare, females with just one affected chromosome can sometimes show symptoms of haemophilia. But because females have two X chromosomes, both chromosomes would need to have a mutation for them to be severely affected by the disease. However, females who do not show signs of haemophilia are often referred to as “carriers” because they can still pass on the mutated gene to their children, even though they have no symptoms of the condition.

MUTATIONS CAN AFFECT YOUR GENETIC INSTRUCTIONS

A mutation can affect the genetic instructions in your body. The instructions can be missing or incorrect, changing the way proteins are produced. This can result in the production of a protein that does not work properly or, in some cases, the protein is not produced at all.

Mutations can take the form of changed nucleotide pairings, extra DNA where it doesn’t belong, missing DNA or repeated DNA.

In people with haemophilia A or B, the genetic mutation affects the body’s ability to produce a protein called factor VIII or factor IX, respectively. These proteins are critical for blood to clot.

THERE ARE THREE TYPES OF GENETIC CONDITIONS

The three types of genetic conditions are single-gene conditions, multi-gene conditions and chromosomal conditions.

  • Monogenic conditions – like haemophilia – are caused by a mutation in a single gene. Other examples include cystic fibrosis and Huntington disease
  • Multifactorial inheritance conditions, or multi-gene conditions, develop from multiple small genetic mutations and can lead to some of the more common diseases we’re familiar with, such as heart disease and diabetes
  • Chromosome disorders are caused by changes to the number or structure of chromosomes. Down’s syndrome is the most common disorder related to this type of abnormality

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