Clinical Outcome Study for Dysferlinopathy

Dysferlinopathy represents a rare group of muscular dystrophies, presenting a particular challenge for the definition of natural history and "trial readiness". In the early days after the cloning of the dysferlin gene, several papers described the clinical phenotype over time of collections of patients leading to the recognition of the "core" phenotypes of Miyoshi Myopathy (MM), LGMD2B and the rarer distal myopathy with anterior tibial involvement. Most of these papers dealt with inbred populations with a limited number of mutations represented. Subsequent studies have reported larger numbers of patients with outbred mutations and extended the clinical spectrum to include onset as young as early childhood and as late as old age, with a large group of patients in whom a clear distinction in their pattern of muscle involvement into Miyoshi or LGMD was not possible, with involvement of both the proximal and distal musculature in most patients, especially as the disease progresses. A limitation of all of these studies however is that with few exceptions, again mainly in inbred groups, long-term follow-up data are not presented and data on clinical progression are collected in different ways making precise comparisons between their conclusions difficult. Nonetheless, the studies overall are in agreement that dysferlinopathy is a chronically progressive condition sometimes with periods where there is a plateauing of muscle function, with variable age at wheelchair dependency and probably a low risk of cardiac and respiratory complications compared to other types of muscular dystrophy. Intriguing suggestions from these publications which require more systematic study include the definition of a particularly good level of sporting prowess before the onset of symptoms and the description of a subacute onset with muscle pain and swelling, both features, if better understood, that potentially could help in our understanding of the pathogenesis of the disease.

Recently, two as yet unpublished studies have addressed the topic of charting the natural history of dysferlinopathy more systematically. In a study of 9 genetically confirmed LGMD2B and MM patients studied over 18 months, Isabel Illa and colleagues found a significant decline in muscle strength in a set of muscle groups measured by manual muscle testing, and in knee flexion measured by quantitative muscle testing, accompanied by a detectable deterioration on MRI imaging in biceps femori and tibialis posterior. Maggie Walter and colleagues assessed the natural course of disease and efficacy of deflazacort treatment in 25 patients (between 25 and 63 years of age) with genetically confirmed dysferlinopathy in a double-blind, cross-over trial. During the first year of the study, they assessed the natural course of disease in 6-month intervals, evaluating MRC scores, quantitative strength measurement by hand-held dynamometry (Citec, Groningen, Netherlands), and torque measurement (M3 diagnose system, Fa. Schnell, Germany), Neuromuscular Symptoms Score (NSS), Timed Function Tests (getting up from lying and sitting position, climbing 4 stairs, running 10m), Vignos Scale, Hammersmith Motor Ability Score, and Global Assessment CGI Scale, quality of life SF-36 scale and laboratory parameters (sodium, potassium, creatinine, urea, GOT, GPT, gamma-GT, CK, blood count, ESR, CRP). Medication (placebo or deflazacort in a cross-over design) was only started in the 2nd year of the study. All patients showed a decline in muscle strength over one year, which was reflected in the tests performed.

It is reassuring that from these data we can conclude that it is likely that there will be changes detectable with time in dysferlinopathy that could inform the design of future clinical trials, but the optimal measurements have yet to be defined and mapped in a much larger group of dysferlinopathy patients representing the entire clinical spectrum of this diverse disease group. Extrapolating from the requirements for studies in other types of muscular dystrophies, including the regulatory advice for establishing pivotal trials of therapies in these disorders, these measures would need to include not only measures of muscle strength, but also of function and some degree of patient reported outcomes. The unpublished results of Isabel Illa and colleagues, as well as another small study of MRI in dysferlinopathy, also show some hope for the use of MRI as a measure of change in muscle over time which might be applicable as an outcome measure. Up until now, muscle MRI has been seen more as a tool for delineating the pattern of muscles involved than for monitoring change - the use of MRI for monitoring disease progression in a non-invasive manner is however attracting a lot of current interest, though more study is needed especially in respect of functional correlates and patient relevance.

The frequency of dysferlinopathy provides a further challenge to the collection of natural history data. The relative frequency of different forms of muscular dystrophy depends to a certain extent on the population studied. Dysferlinopathy appears to be a more common cause of LGMD in Southern European populations than in Northern European ones. Founder mutations exist in only a few small communities. There is little doubt that dysferlinopathy is under-diagnosed and, in fact, the clinical diagnostic process by which dysferlinopathy is diagnosed is also variable. Most laboratories still rely on the suggestion of the diagnosis by muscle immunocytochemistry or (more reliably) immunoblotting. Some laboratories carry out protein testing on monocytes as an alternative screening methodology. The gold standard for dysferlinopathy diagnosis has however become DNA testing, with sequencing carried out in a small number of commercial laboratories as well as a series of diagnostic laboratories in Europe and the USA. The Jain Foundation (www.jain-foundation.org) can help guide those who are unsure about their diagnosis through the process of getting a genetic analysis. Please contact Sarah Shira at the Jain Foundation for help with diagnosis at +1 425 882 1492

With the perspective of different approaches to therapy in dysferlinopathy, a clearer definition of the natural history of the disease and the delineation of suitable outcome measures for clinical trials needs to be prioritised. The current protocol builds on existing national and international networks to bring together a critical mass to address the following specific aims:

1. Define the natural history of dysferlinopathy in a large unselected patient group with respect to age and nature of onset, progression and presence of complications via existing and expanded registries and databases

2. Study a selection of possible outcome measures for dysferlinopathy trials over a three year period in a multicentre evaluation of 150 patients based in centres of excellence for muscular dystrophy diagnosis and management

3. Extend the existing registry activities coordinated by the Jain Foundation to ensure a comprehensive patient registry for dysferlinopathy, within the TREAT-NMD international registry framework.