Muscle Magnetic Resonance Imaging in Patients with Various Clinical Subtypes of LMNA-Related Muscular Dystrophy

[Magnetic resonance imaging for the diagnosis of muscular dystrophy]

OBJECTIVES

To summarize the skeletal muscle magnetic resonance imaging (MRI) features of the lower limbs in common subtypes of muscular dystrophy (MD) and the experience in the application of MRI in the diagnosis of MD.

METHODS

A total of 48 children with MD who were diagnosed by genetic testing were enrolled as subjects. The muscle MRI features of the lower limbs were analyzed. Cumulative fatty infiltration score was calculated for each subtype, and the correlation of cumulative fatty infiltration score with clinical indices was analyzed for Duchenne muscular dystrophy (DMD).

RESULTS

DMD was characterized by the involvement of the gluteus maximus and the adductor magnus. Becker muscular dystrophy was characterized by the involvement of the vastus lateralis muscle. Limb-girdle muscular dystrophy was characterized by the involvement of the adductor magnus, the vastus intermedius, the vastus medialis, and the vastus lateralis muscle. For DMD, the cumulative fatty infiltration score of the lower limb muscles was significantly correlated with age, course of the disease, muscle strength, and motor function (P<0.05), while it was not significantly correlated with the serum creatine kinase level (P>0.05).

CONCLUSIONS

Different subtypes of MD have different MRI manifestations, and MRI may help with the diagnosis and assessment of MD.

Autosomal dominant Emery-Dreifuss muscular dystrophy caused by a mutation in the lamin A/C gene identified by exome sequencing: a case report

Background

Emery-Dreifuss Muscular Dystrophy (EDMD) is an uncommon genetic disease among the group of muscular dystrophies. EDMD is clinically heterogeneous and resembles other muscular dystrophies. Mutation of the lamin A/C (LMNA) gene, which causes EDMD, also causes many other diseases. There is inter and intrafamilial variability in clinical presentations. Precise diagnosis can help in patient surveillance, especially before they present with cardiac problems. Hence, this paper shows how a molecular work-out by next-generation sequencing can help this group of disorders.

Case presentation

A 2-year-10-month-old Javanese boy presented to our clinic with weakness in lower limbs and difficulty climbing stairs. The clinical features of the boy were Gower's sign, waddling gait and high CK level. His father presented with elbow contractures and heels, toe walking and weakness of limbs, pelvic, and peroneus muscles. Exome sequencing on this patient detected a pathogenic variant in the LMNA gene (NM_170707: c.C1357T: NP_733821: p.Arg453Trp) that has been reported to cause Autosomal Dominant Emery-Dreifuss muscular dystrophy. Further examination showed total atrioventricular block and atrial fibrillation in the father.

Conclusion

EDMD is a rare disabling muscular disease that poses a diagnostic challenge. Family history work-up and thorough neuromuscular physical examinations are needed. Early diagnosis is essential to recognize orthopaedic and cardiac complications, improving the clinical management and prognosis of the disease. Exome sequencing could successfully determine pathogenic variants to provide a conclusive diagnosis.

Muscle magnetic resonance imaging in patients with LAMA2-related muscular dystrophy

LAMA2-related muscular dystrophy (LAMA2-MD) is classified into congenital muscular dystrophy type 1A (MDC1A) and autosomal recessive limb-girdle muscular dystrophy-23 (LGMDR23). The purpose of this study was to identify the involvement pattern of thigh muscles of LAMA2-MD patients on magnetic resonance imaging. Fourteen MDC1A and 3 LGMDR23 patients were included, with 21 known and 8 novel LAMA2 disease-causing variants. In LAMA2-MD, the gluteus maximus, anterior (quadriceps femoris) and posterior (adductor magnus and biceps femoris) thigh muscles were extensively and severely affected with fatty infiltration, with relatively sparing of the adductor longus. The pattern of muscle involvement was similar between MDC1A and LGMDR23, but more severe in MDC1A, as well as in LAMA2-MD patients without ambulation. The rather peculiar pattern of the adductor magnus and long head of the biceps femoris first and severely affected in the mid-thigh level was found in LGMDR23. Strong correlation between fatty infiltration and age as well as disease duration was observed for the adductor longus in MDC1A. Edema and atrophy selectively involved in some muscles. The pattern of fatty infiltration on thigh muscle MRI of LAMA2-MD could provide important information for the diagnosis, differential diagnosis and assessment of clinical severity.

In Silico and In Vivo Analysis of Amino Acid Substitutions That Cause Laminopathies

Mutations in the LMNA gene cause diseases called laminopathies. LMNA encodes lamins A and C, intermediate filaments with multiple roles at the nuclear envelope. LMNA mutations are frequently single base changes that cause diverse disease phenotypes affecting muscles, nerves, and fat. Disease-associated amino acid substitutions were mapped in silico onto three-dimensional structures of lamin A/C, revealing no apparent genotype–phenotype connections. In silico analyses revealed that seven of nine predicted partner protein binding pockets in the Ig-like fold domain correspond to sites of disease-associated amino acid substitutions. Different amino acid substitutions at the same position within lamin A/C cause distinct diseases, raising the question of whether the nature of the amino acid replacement or genetic background differences contribute to disease phenotypes. Substitutions at R249 in the rod domain cause muscular dystrophies with varying severity. To address this variability, we modeled R249Q and R249W in Drosophila Lamin C, an orthologue of LMNA. Larval body wall muscles expressing mutant Lamin C caused abnormal nuclear morphology and premature death. When expressed in indirect flight muscles, R249W caused a greater number of adults with wing posturing defects than R249Q, consistent with observations that R249W and R249Q cause distinct muscular dystrophies, with R249W more severe. In this case, the nature of the amino acid replacement appears to dictate muscle disease severity. Together, our findings illustrate the utility of Drosophila for predicting muscle disease severity and pathogenicity of variants of unknown significance.

Skeletal and Cardiac Muscle Disorders Caused by Mutations in Genes Encoding Intermediate Filament Proteins

Intermediate filaments are major components of the cytoskeleton. Desmin and synemin, cytoplasmic intermediate filament proteins and A-type lamins, nuclear intermediate filament proteins, play key roles in skeletal and cardiac muscle. Desmin, encoded by the DES gene (OMIM *125660) and A-type lamins by the LMNA gene (OMIM *150330), have been involved in striated muscle disorders. Diseases include desmin-related myopathy and cardiomyopathy (desminopathy), which can be manifested with dilated, restrictive, hypertrophic, arrhythmogenic, or even left ventricular non-compaction cardiomyopathy, Emery–Dreifuss Muscular Dystrophy (EDMD2 and EDMD3, due to LMNA mutations), LMNA-related congenital Muscular Dystrophy (L-CMD) and LMNA-linked dilated cardiomyopathy with conduction system defects (CMD1A). Recently, mutations in synemin (SYNM gene, OMIM *606087) have been linked to cardiomyopathy. This review will summarize clinical and molecular aspects of desmin-, lamin- and synemin-related striated muscle disorders with focus on LMNA and DES-associated clinical entities and will suggest pathogenetic hypotheses based on the interplay of desmin and lamin A/C. In healthy muscle, such interplay is responsible for the involvement of this network in mechanosignaling, nuclear positioning and mitochondrial homeostasis, while in disease it is disturbed, leading to myocyte death and activation of inflammation and the associated secretome alterations.

International retrospective natural history study of LMNA-related congenital muscular dystrophy

Muscular dystrophies due to heterozygous pathogenic variants in LMNA gene cover a broad spectrum of clinical presentations and severity with an age of onset ranging from the neonatal period to adulthood. The natural history of these conditions is not well defined, particularly in patients with congenital or early onset who arguably present with the highest disease burden. Thus the definition of natural history endpoints along with clinically revelant outcome measures is essential to establishing both clinical care planning and clinical trial readiness for this patient group. We designed a large international cross-sectional retrospective natural history study of patients with genetically proven muscle laminopathy who presented with symptoms before two years of age intending to identify and characterize an optimal clinical trial cohort with pertinent motor, cardiac and respiratory endpoints. Quantitative statistics were used to evaluate associations between LMNA variants and distinct clinical events. The study included 151 patients (median age at symptom onset 0.9 years, range: 0.0–2.0). Age of onset and age of death were significantly lower in patients who never acquired independent ambulation compared to patients who achieved independent ambulation. Most of the patients acquired independent ambulation (n = 101, 66.9%), and subsequently lost this ability (n = 86; 85%). The age of ambulation acquisition (median: 1.2 years, range: 0.8–4.0) and age of ambulation loss (median: 7 years, range: 1.2–38.0) were significantly associated with the age of the first respiratory interventions and the first cardiac symptoms. Respiratory and gastrointestinal interventions occurred during first decade while cardiac interventions occurred later. Genotype–phenotype analysis showed that the most common mutation, p.Arg249Trp (20%), was significantly associated with a more severe disease course. This retrospective natural history study of early onset LMNA-related muscular dystrophy confirms the progressive nature of the disorder, initially involving motor symptoms prior to onset of other symptoms (respiratory, orthopaedic, cardiac and gastrointestinal). The study also identifies subgroups of patients with a range of long-term outcomes. Ambulatory status was an important mean of stratification along with the presence or absence of the p.Arg249Trp mutation. These categorizations will be important for future clinical trial cohorts. Finally, this study furthers our understanding of the progression of early onset LMNA-related muscular dystrophy and provides important insights into the anticipatory care needs of LMNA-related respiratory and cardiac manifestations.

Emery-Dreifuss muscular dystrophy

Emery-Dreifuss muscular dystrophy (EDMD) is a rare muscular dystrophy, but is particularly important to diagnose due to frequent life-threatening cardiac complications. EDMD classically presents with muscle weakness, early contractures, cardiac conduction abnormalities and cardiomyopathy, although the presence and severity of these manifestations vary by subtype and individual. Associated genes include EMD, LMNA, SYNE1, SYNE2, FHL1, TMEM43, SUN1, SUN2, and TTN, encoding emerin, lamin A/C, nesprin-1, nesprin-2, FHL1, LUMA, SUN1, SUN2, and titin, respectively. The Online Mendelian Inheritance in Man database recognizes subtypes 1 through 7, which captures most but not all of the associated genes. Genetic diagnosis is essential whenever available, but traditional diagnostic tools can help steer the evaluation toward EDMD and assist with interpretation of equivocal genetic test results. Management is primarily supportive, but it is important to monitor patients closely, especially for potential cardiac complications. There is a high potential for progress in the treatment of EDMD in the coming years.

Clinical and muscle magnetic resonance image findings in patients with late-onset multiple acyl-CoA dehydrogenase deficiency

Background:

Late-onset multiple acyl-coA dehydrogenase deficiency (MADD) is an autosomal recessive inherited metabolic disorder. It is still unclear about the muscle magnetic resonance image (MRI) pattern of the distal lower limb pre- and post-treatment in patients with late-onset MADD. This study described the clinical and genetic findings in a cohort of patients with late-onset MADD, and aimed to characterize the MRI pattern of the lower limbs.

Methods:

Clinical data were retrospectively collected from clinic centers of Peking University People's Hospital between February 2014 and February 2018. Muscle biopsy, blood acylcarnitines, and urine organic acids profiles, and genetic analysis were conducted to establish the diagnosis of MADD in 25 patients. Muscle MRI of the thigh and leg were performed in all patients before treatment. Eight patients received MRI re-examinations after treatment.

Results:

All patients presented with muscle weakness or exercise intolerance associated with variants in the electron transfer flavoprotein dehydrogenase gene. Muscle MRI showed a sign of both edema-like change and fat infiltration selectively involving in the soleus (SO) but sparing of the gastrocnemius (GA) in the leg. Similar sign of selective involvement of the biceps femoris longus (BFL) but sparing of the semitendinosus (ST) was observed in the thigh. The sensitivity and specificity of the combination of either “SO+/GA–” sign or “BFL+/ST–” sign for the diagnosis of late-onset MADD were 80.0% and 83.5%, respectively. Logistic regression model supported the findings. The edema-like change in the SO and BFL muscles were quickly recovered at 1 month after treatment, and the clinical symptom was also relieved.

Conclusions:

This study expands the clinical and genetic spectrums of late-onset MADD. Muscle MRI shows a distinct pattern in the lower limb of patients with late-onset MADD. The dynamic change of edema-like change in the affected muscles might be a potential biomarker of treatment response.