EU/3/13/1126

On 7 June 2013, orphan designation (EU/3/13/1126) was granted by the European Commission to Prof. Michael Hanna, United Kingdom, for mexiletine hydrochloride for the treatment of non-dystrophic myotonia.

What is non-dystrophic myotonia?

Non-dystrophic myotonia is a term used to describe a group of inherited muscle disorders where muscles are slow to relax after contraction. The slow relaxation of the muscles causes symptoms such as stiffness and pain, but does not cause the progressive weakening of the muscles seen in ‘myotonic dystrophy’, another muscle disorder.

Non-dystrophic myotonia is caused by abnormalities in the ion channels, tiny pores in the muscle cells that control the passage of charged particles (ions) such as sodium or chloride and play a key role in the contraction and relaxation of muscles.

Non-dystrophic myotonia is chronically debilitating due to the pain and muscle stiffness, which are associated with frequent falls and disability.

What is the estimated number of patients affected by the condition?

At the time of designation, non-dystrophic myotonia affected approximately 1 in 10,000 people in the European Union (EU). This was equivalent to a total of around 51,000 people*, and is below the ceiling for orphan designation, which is 5 people in 10,000. This is based on the information provided by the sponsor and the knowledge of the Committee for Orphan Medicinal Products (COMP).

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* Disclaimer: For the purpose of the designation, the number of patients affected by the condition is estimated and assessed on the basis of data from the European Union (EU 27), Norway, Iceland and Liechtenstein. This represents a population of 509,000,000 (Eurostat 2013).

What treatments are available?

At the time of the orphan designation, the anti-arrhythmia medicine mexiletine was authorised in some EU Member States to treat non-dystrophic myotonia.

The sponsor has provided sufficient information to show that mexiletine hydrochloride might be of significant benefit for patients with non-dystrophic myotonia because mexiletine has been in short supply in the EU and the orphan designation may help address the problem. This assumption will need to be confirmed at the time of marketing authorisation, in order to maintain the orphan status.

How is this medicine expected to work?

Mexiletine hydrochloride works by blocking ion channels for sodium ions in the muscle cells. These sodium channels play a role in the contraction and relaxation of muscles and by blocking them, the medicine helps reduce the rate of contractions as well as the stiffness that occurs when the contractions are prolonged.

What is the stage of development of this medicine?

The effects of the medicinal product have been evaluated in experimental models.

At the time of submission of the application for orphan designation, clinical trials with the medicinal product in patients with non-dystrophic myotonia were ongoing.

At the time of submission, the medicinal product was not authorised anywhere in the EU for non-dystrophic myotonia. Orphan designation of the medicinal product had been granted in the United States for the condition.

In accordance with Regulation (EC) No 141/2000 of 16 December 1999, the COMP adopted a positive opinion on 17 April 2013 recommending the granting of this designation.

Opinions on orphan medicinal product designations are based on the following three criteria:

• the seriousness of the condition;
• the existence of alternative methods of diagnosis, prevention or treatment;
• either the rarity of the condition (affecting not more than 5 in 10,000 people in the EU) or insufficient returns on investment.

Designated orphan medicinal products are products that are still under investigation and are considered for orphan designation on the basis of potential activity. An orphan designation is not a marketing authorisation. As a consequence, demonstration of quality, safety and efficacy is necessary before a product can be granted a marketing authorisation.

The Committee for Orphan Medicinal Products reviews the orphan designation of a product if it is approved for marketing authorisation.