FHL1-related myopathy may not be classified by reducing bodies in muscle biopsy

A comprehensive study of skeletal muscle imaging in FHL1-related reducing body myopathy

OBJECTIVE

FHL1-related reducing body myopathy is an ultra-rare, X-linked dominant myopathy. In this cross-sectional study, we characterize skeletal muscle ultrasound, muscle MRI, and cardiac MRI findings in FHL1-related reducing body myopathy patients.

METHODS

Seventeen patients (11 male, mean age 35.4, range 12-76 years) from nine independent families with FHL1-related reducing body myopathy underwent clinical evaluation, muscle ultrasound (n = 11/17), and lower extremity muscle MRI (n = 14/17), including Dixon MRI (n = 6/17). Muscle ultrasound echogenicity was graded using a modified Heckmatt scale. T1 and STIR axial images of the lower extremity muscles were evaluated for pattern and distribution of abnormalities. Quantitative analysis of intramuscular fat fraction was performed using the Dixon MRI images. Cardiac studies included electrocardiogram (n = 15/17), echocardiogram (n = 17/17), and cardiac MRI (n = 6/17). Cardiac muscle function, T1 maps, T2-weighted black blood images, and late gadolinium enhancement patterns were analyzed.

RESULTS

Muscle ultrasound showed a distinct pattern of increased echointensity in skeletal muscles with a nonuniform, multifocal, and "geographical" distribution, selectively involving the deeper fascicles of muscles such as biceps and tibialis anterior. Lower extremity muscle MRI showed relative sparing of gluteus maximus, rectus femoris, gracilis, and lateral gastrocnemius muscles and an asymmetric and multifocal, "geographical" pattern of T1 hyperintensity within affected muscles. Cardiac studies revealed mild and nonspecific abnormalities on electrocardiogram and echocardiogram with unremarkable cardiac MRI studies.

INTERPRETATION

Skeletal muscle ultrasound and muscle MRI reflect the multifocal aggregate formation in muscle in FHL1-related reducing body myopathy and are practical and informative tools that can aid in diagnosis and monitoring of disease progression.

Identification of novel FHL1 mutations associated with X-linked scapuloperoneal myopathy in unrelated Chinese patients

Mutations in the FHL1 gene can be associated with a variety of X-linked myopathies and cardiomyopathies, among which X-linked dominant scapuloperoneal myopathy is a rare phenotype. We collected the clinical data of two unrelated Chinese patients with X-linked scapuloperoneal myopathy and analyzed their clinical, pathological, muscle imaging, and genetic features. Both patients were characterized by scapular winging, bilateral Achilles tendon contractures, and weakness in shoulder-girdle and peroneal muscles. Muscle biopsy revealed myopathic changes, and no reducing bodies were found. Muscle magnetic resonance imaging was dominated by fatty infiltration, with minor edema-like findings. Genetic analysis revealed two novel mutations in the FHL1 gene: c.380T > C (p.F127S) and c.802C > T (p.Q268*), which were located in the LIM2 domain and the C-terminal sequence, respectively. To our knowledge, this is the first report of X-linked scapuloperoneal myopathy in the Chinese population. Our findings broadened the genetic and ethnic spectrum of FHL1-related disorders and proposed to look for variants in the FHL1 gene when scapuloperoneal myopathy is observed in the clinical work.

Reducing body myopathy - A new pathogenic FHL1 variant and literature review

Reducing body myopathy (RBM) is a rare disease marked by progressive muscle weakness caused by a mutation in FHL1 gene. We describe a new pathogenic variant and contrasted it with 44 other cases identified in the literature. A male child presented at age 3 suffering frequent falls and progressive muscular weakness. At age 8, he was wheelchair-bound and required ventilatory support. His mother and sister died due to the same problem. Creatine kinase was 428 IU/L (<190). Muscle biopsy showed typical reducing bodies, and genetic analysis identified a novel pathogenic hemizygous variant, c.370_375del. We identified 44 previous reported cases separated in two groups: 28 cases with mean age onset 7.6 ± 5 years and 16 with 26.7 ± 4.2 years. The time for the diagnosis was shorter to younger group. The initial symptoms, rigid spine, contractures, scoliosis and axial and neck weaknesses, dysphagia, cardiac involvement, were predominant in younger group. The variant c.369C > G predominated in younger group and c.448T > C in older one. Pathogenic variants positions seemed related to severe phenotype. Most wheelchair patients belonged to younger group. The data from this compilation and our case provided a general characterization spectrum and prognosis between two groups of age onset with RBM.