Research Letters

Failure of early diagnosis in symptomatic Duchenne muscular dystrophy

Duchenne Muscle dystrophy (DMD) is a X-linked inherited disease predominantly caused by severe mutations in DMD gene leading to absence of dystrophin protein. Here we report a 14-year-old Mongolian boy suffering from proximal muscle weakness, pseudohypertrophic deltoid and gastrocnemius muscles since early childhood. Lactate dehydrogenase (LDH) and creatine kinase (CK) levels were elevated. Mutation analysis including MLPA and sequencing of the DMD gene revealed a hemizygous silent variant, c.1329C>T (p.Ser443=) in exon 11. This silent mutation, listed in the SNP database (rs1060502631), was described as a variant of unknown significance (VUS) in ClinVar database. cDNA analysis demonstrated partial skipping of exon 11 due to this mutation. Although silent mutations are usually considered non-pathogenic, our case emphasizes that silent mutations can be potentially pathogenic. Hence, if silent variants are not annotated in database or not known to be benign, they should be analysed further at cDNA level.

La distrofia muscular de Duchenne (DMD) es la miopatía más frecuente en niños, con una prevalencia mundial de aproximadamente 0,5 por cada 10.000 varones. Se caracteriza por una debilidad muscular progresiva al inicio de la infancia con aparición posterior de complicaciones musculoesqueléticas, respiratorias y cardíacas que ocasionan discapacidad, dependencia y muerte prematura. Actualmente su tratamiento se fundamenta en medidas sintomáticas multidisciplinares que han modificado favorablemente el curso de la enfermedad, por lo que resulta crucial establecer unas directrices claras y actualizadas que permitan tanto una detección temprana de la enfermedad como un adecuado tratamiento y seguimiento de sus posibles complicaciones.

Con el fin de obtener una visión general de los aspectos abordados por las guías actuales y detectar aquellos en los que todavía no existe un consenso y su abordaje sea relevante, se realizó una revisión de la literatura en la base de datos biomédicas de los últimos 10 años. El grado de evidencia y el nivel de recomendación de la información obtenida se clasificaron y ordenaron de acuerdo con los criterios de la American Academy of Neurology (AAN).

El abordaje de la DMD debe ser multidisciplinar y ajustado al perfil del paciente y su grado de evolución clínica, comprendiendo, además del tratamiento basado en corticoides, medidas a nivel gastrointestinal, respiratorio, cardiaco, fisioterapéutico y ortopédico dirigidas a mejorar la calidad de vida de los pacientes. Los estudios genéticos desempeñan un papel clave en el manejo de la enfermedad, tanto en la detección de casos y posibles portadoras como en la caracterización de la mutación implicada y el desarrollo de nuevas terapias.

Duchenne muscular dystrophy (DMD) is the most common myopathy in children, with a worldwide prevalence of approximately 0.5 cases per 10,000 male births. It is characterised by a progressive muscular weakness manifesting in early childhood, with the subsequent appearance of musculoskeletal, respiratory, and cardiac complications, causing disability, dependence, and premature death. Currently, DMD is mainly managed with multidisciplinary symptomatic treatment, with favourable results in terms of the progression of the disease. It is therefore crucial to establish clear, up-to-date guidelines enabling early detection, appropriate treatment, and monitoring of possible complications.

We performed a literature search of the main biomedical databases for articles published in the last 10 years in order to obtain an overview of the issues addressed by current guidelines and to identify relevant issues for which no consensus has yet been established. The degree of evidence and level of recommendation of the information obtained were classified and ordered according to the criteria of the American Academy of Neurology.

DMD management should be multidisciplinary and adapted to the patient's profile and the stage of clinical progression. In addition to corticotherapy, treatment targeting gastrointestinal, respiratory, cardiac, and orthopaedic problems, as well as physiotherapy, should be provided with a view to improving patients’ quality of life. Genetic studies play a key role in the management of the disease, both in detecting cases and potential carriers and in characterising the mutation involved and developing new therapies.

We aimed to review the history of newborn screening for three neuromuscular disorders (Duchenne muscular dystrophy, Pompe disease, and spinal muscular atrophy [SMA]) to determine best practices.

The history of newborn screening for Duchenne muscular dystrophy began in 1975 with the measurement of creatinine kinase on newborn male blood spots from two Midwestern hospitals in the United States. Over the next 40 years, ten programs were implemented around the globe although none currently remain. The first experimental pilot program for Pompe disease began in 2005 in Taiwan. In 2013, Missouri was the first US state to implement Pompe newborn screening before its inclusion in the Recommended Uniform Screening Panel (RUSP) in 2015 by the Advisory Committee on Heritable Disorders in Newborns and Children (United States). In 2008, SMA was reviewed and rejected for inclusion in the RUSP because no treatment existed. With the approval of nusinersen in late 2016, spinal muscular atrophy is being reconsidered for the RUSP.

A condition should meet public health screening criteria to be included in the RUSP. Duchenne muscular dystrophy, Pompe, and SMA challenge traditional screening criteria: Duchenne muscular dystrophy does not present in infancy and lacks effective treatment; Pompe and SMA may not present until adulthood; and safety and efficacy of long-term intrathecal treatment for SMA is unknown. Potential reproductive benefit and improved research recruitment do not justify a public health screening program.

This review provides lessons that could benefit US public health departments as they consider expanding screening to include neuromuscular disorders like Duchenne muscular dystrophy, Pompe, and SMA.

Toe walking refers to the lack of heel strike during the stance phase of the gait cycle. It is a common variation of normal gait development in children. Persistent toe walking past 2–3 years of age warrants further evaluation as toe walking can be associated with cerebral palsy, muscular dystrophy, and autism spectrum disorders. The diagnosis of idiopathic toe walking is a diagnosis of exclusion used for children with persistent toe walking and no associated medical condition. Despite variable pathophysiology, the treatment of toe walking has similarities across diagnoses as it is focused on the maintenance of range of motion through the ankle.

Despite all the advances in diagnosis and management of Duchenne muscular dystrophy over the past 50 years, the average age at diagnosis in most countries in the world around is still around 4–5 years. This retrospective study investigates the age at diagnosis in Italy in the past 10 years. We report findings from 384 boys who were diagnosed with DMD from 2005 to 2014. The mean age at first medical contact, which raised the suspicion of DMD, was 31 months. The mean age at diagnosis was 41 months. The finding that more frequently brought to suspect a DMD was the incidental finding of consistent elevated creatine kinase serum level detected during routine assessments in children undergoing general anesthesia or with intercurrent illness. This was followed by motor delay and signs of muscle weakness. Initial concerns were raised by general pediatricians (29%), specialists at tertiary centers (35%) or first level hospitals (23%). In children presenting incidental elevated creatine kinase values the diagnosis was achieved earlier than in children presenting a developmental delay. The mean age at diagnosis in our cohort was about 10–12 months lower than that reported in other countries.

Cardiomyopathy is a major source of morbidity and mortality in Duchenne muscular dystrophy (DMD) patients now that respiratory care has improved. There is currently no definitive evidence guiding the management of DMD-associated cardiomyopathy (DMD-CM). The objective of this systematic review was to evaluate the effectiveness of pharmacotherapies for the prevention and/or management of DMD-CM and to determine the optimal timing to commence these interventions. A systematic search was conducted in January 2016 using MEDLINE, EMBASE and CINAHL databases and grey literature sources for studies evaluating the use of angiotensin-converting enzyme (ACE) inhibitors, angiotensin receptor blockers, beta-blockers or aldosterone antagonists. Study quality assessment was conducted using the Downs and Black quality assessment checklist. PRISMA reporting guidelines were used. Of the 15 studies included in this review, most were of low methodological quality. Meta-analysis was not possible due to heterogeneity of studies. ACE inhibitors, angiotensin receptor blockers, beta-blockers and/or aldosterone antagonists tended to improve or preserve left ventricular systolic function and delay the progression of DMD-CM. While there is evidence supporting the use of heart failure medication in patients with DMD, data regarding these interventions for delaying the onset of DMD-CM and when to initiate therapy are lacking. PROSPERO registration: CRD42015029555.