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Disease Profile

Reducing body myopathy

Prevalence estimates on Rare Medical Network websites are calculated based on data available from numerous sources, including US and European government statistics, the NIH, Orphanet, and published epidemiologic studies. Rare disease population data is recognized to be highly variable, and based on a wide variety of source data and methodologies, so the prevalence data on this site should be assumed to be estimated and cannot be considered to be absolutely correct.

<1 / 1 000 000

US Estimated

Europe Estimated

Age of onset






Autosomal dominant A pathogenic variant in only one gene copy in each cell is sufficient to cause an autosomal dominant disease.


Autosomal recessive Pathogenic variants in both copies of each gene of the chromosome are needed to cause an autosomal recessive disease and observe the mutant phenotype.


dominant X-linked dominant inheritance, sometimes referred to as X-linked dominance, is a mode of genetic inheritance by which a dominant gene is carried on the X chromosome.


recessive Pathogenic variants in both copies of a gene on the X chromosome cause an X-linked recessive disorder.


Mitochondrial or multigenic Mitochondrial genetic disorders can be caused by changes (mutations) in either the mitochondrial DNA or nuclear DNA that lead to dysfunction of the mitochondria and inadequate production of energy.


Multigenic or multifactor Inheritance involving many factors, of which at least one is genetic but none is of overwhelming importance, as in the causation of a disease by multiple genetic and environmental factors.


Not applicable



Congenital and Genetic Diseases; Nervous System Diseases


The following summary is from Orphanet, a European reference portal for information on rare diseases and orphan drugs.

Orpha Number: 97239

Reducing body myopathy (RBM) is a rare muscle disorder marked by progressive muscle weakness and the presence of characteristic inclusion bodies in affected muscle fibres.

The prevalence is unknown: although some sporadic cases have been described, only four families with RBM have been reported in the literature so far.

Clinical description
The age of onset, speed of progression and severity of the disease vary significantly between patients, even between affected members of the same family. Although early development is generally normal (up to 2 years of age), onset during infancy or early childhood appears to be associated with severe myopathy, hypotonia and rapidly progressive muscle weakness leading to death due to respiratory insufficiency within the first five years of life. Onset during childhood or adulthood is characterised by mainly proximal muscle weakness, a rigid spine syndrome and a slowly progressive disease course.

Both sporadic and familial cases of RBM are caused by mutations in the gene encoding the four-and-a-half LIM domain 1 protein (FHL1; Xq27.2).

Diagnostic methods
As the clinical picture is highly variable (EMG reveals mixed myogenic patterns), diagnosis relies on recognition of the typical histopathological findings at muscle biopsy: the non-membrane-bound inclusions reduce nitro-blue tetrazolium (hence the name `reducing body myopathy') and are located in the cytoplasm, usually close to the degenerating nucleus. Electron microscopy reveals that the inclusions consist of a fine granular material and immunohistochemical analysis reveals the presence of aggresome-like proteins.

Differential diagnosis
The differential diagnosis should include other disorders with reducing bodies (e.g. acid maltase deficiency) and other congenital myopathies in familial cases (see these terms). Sarcotubular myopathy may also be considered in patients with less severe forms of the disease.

Genetic counseling
The mode of transmission remains unclear. There are no reports of male-to-male transmission in familial cases and cases of severely affected females have been reported. X-linked dominant, semi-dominant and recessive inheritance have been suggested and skewed X-inactivation has not been excluded.

Management and treatment
Management is supportive and should be multidisciplinary (involving a neurologist, orthopaedic surgeon and physical therapist).

The prognosis is generally severe: disease progression results in loss of ambulation, and death due to respiratory failure occurs even in patients with later-onset slowly progressive forms of the disease.

Visit the Orphanet disease page for more resources.


This table lists symptoms that people with this disease may have. For most diseases, symptoms will vary from person to person. People with the same disease may not have all the symptoms listed. This information comes from a database called the Human Phenotype Ontology (HPO) . The HPO collects information on symptoms that have been described in medical resources. The HPO is updated regularly. Use the HPO ID to access more in-depth information about a symptom.

Medical Terms Other Names
Learn More:
5%-29% of people have these symptoms
Dilated cardiomyopathy
Stretched and thinned heart muscle
Percent of people who have these symptoms is not available through HPO
Absent tendon reflexes
Elevated serum creatine kinase
Elevated blood creatine phosphokinase
Elevated circulating creatine phosphokinase
Elevated creatine kinase
Elevated serum CPK
Elevated serum creatine phosphokinase
High serum creatine kinase
Increased CPK
Increased creatine kinase
Increased creatine phosphokinase
Increased serum CK
Increased serum creatine kinase
Increased serum creatine phosphokinase

[ more ]

Flexion contracture
Flexed joint that cannot be straightened
Frequent falls
Prominent swayback
Decreased reflex response
Decreased reflexes

[ more ]

Increased variability in muscle fiber diameter
Hunched back
Round back

[ more ]

Proximal muscle weakness
Weakness in muscles of upper arms and upper legs
Rapidly progressive
Worsening quickly
Respiratory insufficiency due to muscle weakness
Decreased lung function due to weak breathing muscles
Short neck
Decreased length of neck
Spinal rigidity
Reduced spine movement
X-linked dominant inheritance
X-linked inheritance

Learn more

These resources provide more information about this condition or associated symptoms. The in-depth resources contain medical and scientific language that may be hard to understand. You may want to review these resources with a medical professional.

In-Depth Information

  • The Monarch Initiative brings together data about this condition from humans and other species to help physicians and biomedical researchers. Monarch’s tools are designed to make it easier to compare the signs and symptoms (phenotypes) of different diseases and discover common features. This initiative is a collaboration between several academic institutions across the world and is funded by the National Institutes of Health. Visit the website to explore the biology of this condition.
  • Online Mendelian Inheritance in Man (OMIM) is a catalog of human genes and genetic disorders. Each entry has a summary of related medical articles. It is meant for health care professionals and researchers. OMIM is maintained by Johns Hopkins University School of Medicine. 
    Severe early-onset reducing body myopathy
    Childhood-onset reducing body myopathy
  • Orphanet is a European reference portal for information on rare diseases and orphan drugs. Access to this database is free of charge.
  • PubMed is a searchable database of medical literature and lists journal articles that discuss Reducing body myopathy. Click on the link to view a sample search on this topic.