This is our fifth instalment from our guest blogger, who writes about various aspects of living with rare conditions. All posts under the title ‘Treasure the Exceptions’ are written by our guest blogger, pro bono. The information is supplied by members of various patient groups, clinicians etc. Whenever possible, permission is sought for direct quotations and anonymity is respected when requested.

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Treasure the Exceptions. When it comes to sensory processing: We’re Rare and We Rock.*

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How rare is ‘rare’?

I wish I had a fiver for every time I’ve been asked about the prevalence of MdDS. I also wish I could give an answer. Although MdDS is listed on Check Orphan and the Global Genes registry in the USA, case numbers are not given on these lists. And (as of January 2015) MdDS is not included in the list of conditions covered by any of the official Rare Diseases Registries in Europe. So, in the absence of international central data-gathering, researchers can only calculate prevalence based on estimations extrapolated from the numbers of patients they see. But since certain centres of excellence will see a disproportionately high number of MdDS patients (as word spreads about the expertise of clinicians in these clinics) this may skew the figures.

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Meanwhile, with the advent of the Isabel symptom checker and the rise of internet patient groups, many people with MdDS can now self-diagnose. They may decide not to go through the ‘ruling-out’ tests for a formal diagnosis as they know these tests can make symptoms worse and may prolong episodes. I encourage people to seek an official diagnosis so that they can be involved in treatment trials, if there are any in their area. But even when they do, they run the risk of misdiagnosis/mistreatment unless they can access the experts. So the prevalence of MdDS may remain a mystery for many years to come.

What is clear is that papers about MdDS, compared to those written about other orphan conditions, are very rare. With two members of my family affected by MdDS – and on behalf of the MdDS community – I hope this situation changes soon. I applaud our rare researchers and am so grateful for all the help and information they have given me personally.

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Since joining RDUK I’ve become interested in the prevalence of rare conditions generally – and the estimated number of them in different populations and age groups. Conditions that are common in some parts of the world are considered rare elsewhere and most childhood cancers are considered to be rare because so few children get cancer, compared to the adult population. So it is not surprising that the number of rare conditions is hard to estimate, especially given that there are conditions which are so rare that they have yet to be named. Meanwhile some rare diseases sites and registries include conditions that have a lifetime incidence, but are not chronic. But others don’t, so this may further confuse the picture with respect to the number of conditions said to be rare.

In terms of prevalence, the definitions used in some medical literature and national health plans consider rare to mean 1/1000 people whereas others use a measure of 1/200,000 – which is a huge magnitude of difference. One of my favourite rare disease advocacy organisations, The Rare Diseases Foundation in Canada uses the measure of fewer than 1/2000. But they make a very interesting point which is that ‘undiagnosed patients push these numbers even higher’.

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What if all rare conditions are under-diagnosed as much as may be happening with Acromegaly? What if the under-diagnosis of some or all rare conditions is far more prevalent in some countries than in others? How would that skew the estimated percentages of people with rare conditions, internationally? What does seem clear is that, now many patients can self-diagnose relatively easily, any quantitative estimation of the prevalence of rare conditions is likely to need constant revision.

This captivating image sums up the picture of rare conditions, for me. With one deep red bloom set amongst the pastels it is easy to identify the one that stands out for its difference. Yet – with a lot of the flowers still in bud – the rare bloom may prove not to be the exception, after all.

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I would like to thank Monique Wilson for permission to use the flower photograph. Ms Wilson also suffers from MdDS and lost her career, as a result. Her indomitable spirit shines through her photographic work and inspires me daily. If you have an experience of a rare condition that you’d be willing to share (or any comments about the ‘treasure the exceptions’ blogs) please contact [email protected] I am particularly keen to hear from any clinicians who have patients with rare conditions and from those involved in research.

*This is the logo for a new group (founded by our blogger) which was established to campaign for people with MdDS in the UK.

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