Rare diseases: why diagnosis can be so difficult

It's frightening when your child has symptoms that are troubling the doctors. They scratch their heads and bring in specialists. They have no answers and conduct test after test. You search online looking for an answer and your fear and frustration gets larger and larger. What if what your child has is one of the thousands of rare or "orphan" diseases that are known to exist?

People with rare diseases face a number of problems. For example:

  • There may be few specialists or experts in a rare disease.
  • Access to experts is limited.
  • Diagnosis is often delayed, which delays treatment.
  • Information and scientific knowledge about a rare disease may be lacking.

What is a rare or "orphan" disease?

The US National Institutes of Health Office of Rare Disease Research (ORDR) recognizes approximately 7,000 rare diseases. How to classify a rare disease differs depending on where you live in the world. For example, in Europe it is one with fewer than 2,000 patients; in the US, fewer than 200,000 patients; and in Japan, fewer than 50,000 patients.

Rare disorders range from relatively familiar but still low-incidence conditions (e.g., cerebral palsy or multiple sclerosis) to obscure, difficult-to-pronounce genetic and metabolic disorders (e.g., chromosome 3, monosomy 3p or short chain acyl-CoA-dehydrogenase deficiency).

Why is it so difficult to get a diagnosis for a rare disease?

The main reason it can be hard to reach a diagnosis is simply because a disease or disorder is so rare that it is unrealistic for a doctor to be familiar with every one of the thousands of rare conditions.

Another reason that it can be difficult to diagnose a rare disease is because many of these conditions are genetic. While some soon-to-be parents undergo genetic testing to identify potential genetic disorders, some do not. You could have been born with an unidentified genetic disorder that lays dormant deep in the body's cells from birth that suddenly triggers symptoms that can seem to come from out of nowhere.

Over 80% of the approximately 7,000 rare diseases are caused by a defective gene(s). Take for example one such single-gene mutation called Gaucher disease. If you've never heard of it, you're not alone. Only about 100,000 people worldwide have Gaucher disease. Despite its rarity, Gaucher disease is the most common disorder among a group of 40 or more diseases called lysosomal storage disorders (LSDs).

In LSDs, genetic mutations damage enzymes that would normally break down substances within the cells. This leads to an abnormal buildup and storage of substances that can interfere with the normal functioning of cells and organs. In the case of the most common form of Gaucher disease (type 1), fatty substances can accumulate in the liver, spleen, lungs, bone marrow, and brain.

Diagnosis for lesser-known diseases like Gaucher disease can be confusing due to symptoms that at first appear unrelated or hard to relate. The symptoms of Gaucher disease include bone pain and fractures, anemia, breathing problems, and swelling of affected organs. You might visit a doctor concerned about bone pain, and a doctor may suspect any number of other issues before considering a disorder like Gaucher disease – like injury, infection, overuse, or the beginnings of osteoporosis.

And unfortunately, when a person has had to go from doctor to doctor or has been in and out of hospitals without receiving a definite diagnosis, medical professionals may appear to question a patient's integrity and not take their symptoms seriously. In some instances, people are told that they don't "fit the profile" for disease, or that the symptoms are "all in your head." Precious time that could be used for treatment or investigation gets lost in misinterpretation or in the shuffle from one doctor or specialist to the next.

It can take perseverance to acquire a diagnosis for rare diseases. But there are definite benefits to staying the course and being a proactive patient.

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