Clinical characteristics.

The spectrum of ANO5-related muscle disease is a continuum that ranges from asymptomatic hyperCKemia and exercise-induced myalgia to proximal and/or distal muscle weakness. The most typical presentation is limb-girdle muscular dystrophy R12 anoctamin-5-related (LGMD-R12) with late-onset proximal lower limb weakness in the fourth or fifth decade (range: age 15-70 years). Less common is Miyoshi muscular dystrophy 3 (MMD3) with adult-onset calf distal myopathy (onset around age 30 years). Incidental hyperCKemia may be present even earlier. Initial symptoms are walking difficulties, reduced sports performance, and difficulties in standing on toes as well as nonspecific exercise myalgia and/or burning sensation in the calf muscles. Muscle weakness and atrophy are frequently asymmetric. Cardiac findings can include cardiomyopathy and arrhythmias and/or left ventricular dysfunction. Bulbar or respiratory symptoms have been mild and infrequent. Females have milder disease manifestations than males. Disease progression is slow in both LGMD-R12 and MMD3; ambulation is preserved until very late in the disease course. Life span is normal.

Diagnosis/testing.

The diagnosis of ANO5-related muscle disease is established in a proband with suggestive findings and biallelic pathogenic variants in ANO5 identified by molecular genetic testing.

Management.

Treatment of manifestations: No definitive treatments for ANO5-related muscle disease exists. Management is tailored to the individual. To assist with decreased mobility, the following are suggested: weight control to avoid obesity, physical therapy to promote mobility and prevent contractures, and use of mechanical aids to help ambulation and mobility.

Surveillance: Evaluate muscle strength and functional status every six to 12 months; EKG every three years.

Agents/circumstances to avoid: Avoid heavy muscle force training of weak muscles. Avoid cholesterol-lowering agents (e.g., statins) when possible. The use of statins requires extra monitoring of clinical status, especially at the beginning of treatment.

Genetic counseling.

ANO5-related muscle disease is inherited in an autosomal recessive manner. If both parents are known to be heterozygous for an ANO5 pathogenic variant, each sib of an affected individual has at conception a 25% chance of being affected, a 50% chance of being an asymptomatic carrier, and a 25% chance of being unaffected and not a carrier. Once the ANO5 pathogenic variants have been identified in an affected family member, carrier testing for at-risk relatives and prenatal/preimplantation genetic testing are possible.

Suggestive Findings

ANO5-related muscle disease should be suspected in probands with the following clinical, laboratory, electrophysiology, imaging, and histopathology findings and family history.

Clinical findings

• Asymmetric muscle weakness and atrophy, especially in the thigh muscles, with late adult onset (mean onset: age 35 years)
• Calf distal myopathy of early adult onset (mean onset: age 30 years)
• Exercise-induced myalgia

Laboratory findings. Serum creatine kinase (CK) concentration is markedly elevated (≥2-3 times – and usually 10-50 times – the upper limit of normal).

Electrophysiology findings. EMG shows myopathic changes or may be normal in mildly affected individuals.

Imaging findings. CT and MRI show fatty degeneration of the gastrocnemius medialis muscle in most affected individuals with involvement of the soleus and posterior thigh muscles with disease progression (see Figure 1).

Figure 1.

MR images of right (R) and left (L) upper (A) and lower (B) legs in an individual with ANO5-related muscle disease A. Fatty degenerative changes in posterior thigh muscles in the left vastus medialis and intermedius muscles (L)

Histopathology findings. Muscle biopsy shows scattered necrotic fibers or nonspecific myopathic or dystrophic findings.

Family history is consistent with autosomal recessive inheritance (e.g., affected sibs and/or parental consanguinity). Absence of a known family history does not preclude the diagnosis.

Establishing the Diagnosis

The diagnosis of ANO5-related muscle disease is established in a proband with suggestive findings and biallelic pathogenic (or likely pathogenic) variants in ANO5 identified by molecular genetic testing (see Table 1).

Note: (1) Per American College of Medical Genetics and Genomics / Association for Molecular Pathology variant interpretation guidelines, the terms "pathogenic variant" and "likely pathogenic variant" are synonymous in a clinical setting, meaning that both are considered diagnostic and can be used for clinical decision making [Richards et al 2015]. Reference to "pathogenic variants" in this GeneReview is understood to include likely pathogenic variants. (2) Identification of biallelic ANO5 variants of uncertain significance (or of one known ANO5 pathogenic variant and one ANO5 variant of uncertain significance) does not establish or rule out the diagnosis.

Because the phenotype of ANO5-related muscle disease is indistinguishable from many other inherited muscle disorders, molecular genetic testing can include a combination of gene-targeted testing (multigene panel) and comprehensive genomic testing (exome sequencing, genome sequencing). Gene-targeted testing requires that the clinician determine which gene(s) are likely involved (see Option 1), whereas comprehensive genomic testing does not (see Option 2).

Note: Single-gene testing (sequence analysis of ANO5, followed by gene-targeted deletion/duplication analysis) is rarely useful and typically NOT recommended.

Clinical Description

The spectrum of ANO5-related muscle disease is a continuum ranging from exercise-induced myalgia and hyperCKemia to proximal and/or distal muscle weakness. The most common presentation is late-onset proximal lower limb weakness (limb-girdle muscular dystrophy R12 anoctamin-5-related [LGMD-R12]) [Bolduc et al 2010, Hicks et al 2011, de Bruyn et al 2023]. Less common is early adult-onset calf distal myopathy (Miyoshi muscular dystrophy 3 [MMD3]) [Hicks et al 2011, Ten Dam et al 2019, de Bruyn et al 2023]. To date, more than 500 individuals have been identified with biallelic pathogenic variants in ANO5. The following description of the phenotypic features associated with this condition is based on these reports.

Onset of the proximal weakness in LGMD-R12 is in the fourth or fifth decade (range: age 15-70 years); onset of calf weakness in MMD3 is around age 30 years. Incidental hyperCKemia may be present even earlier. Initial symptoms are walking difficulties, reduced sports performance, and difficulties in standing on toes as well as nonspecific exercise myalgia and/or burning sensation in the calf muscles. Episodes of symptomatic rhabdomyolysis are also possible but very rare [Bolduc et al 2010, Hicks et al 2011, Penttilä et al 2012, Papadopoulos et al 2017, Ten Dam et al 2019, de Bruyn et al 2023].

Musculoskeletal. In individuals with LGMD-R12, muscle weakness is mainly proximal and more pronounced in the lower limbs; however, many affected individuals also have mild-to-moderate proximal upper limb involvement, usually affecting biceps brachii and/or scapular muscles. Some individuals develop knee hyperextension secondary to quadriceps muscle weakness. Contractures are rare but can occur in the Achilles tendons of some individuals. An increasing number of individuals require walking aids, starting after about age 40 years, but affected individuals rarely become wheelchair bound.

In MMD3, calf hypertrophy and exercise myalgia can occur before apparent weakness and later calf atrophy. Clinical manifestations can be mild or subjectively nonexistent even with clear changes observed on muscle imaging. Individuals with distal onset may have proximal lower limb weakness in the later stages of the disease. Distal upper limb weakness has not been reported.

Muscle weakness and atrophy are frequently asymmetric (see Figure 2).

Figure 2.

Asymmetric atrophy of the muscles of the left calf in an individual with ANO5-related muscle disease

Persistent hyperCKemia does not seem to cause secondary adverse effects.

Cardiac findings. In the largest ANO5-related muscle disease cohort to date, severe cardiac abnormalities were very rare [de Bruyn et al 2023] and they occurred more commonly in individuals with LGMD-R12 than in individuals with asymptomatic hyperCKemia. Cardiac rhythm disturbances were mostly mild and were present in 16% of individuals, whereas dilated or hypertrophic cardiomyopathy were reported in 5% of individuals.

Other. Respiratory dysfunction requiring ventilatory support is extremely rare.

Sex differences. Females tend to have milder disease manifestations than males [de Bruyn et al 2023]. It is possible females are underrepresented in the reports due to milder disease course, which may be only hyperCKemia with or without myalgia or mild muscle weakness.

Progression and life span. Disease progression is slow in both LGMD-R12 and MMD3; ambulation is preserved until very late in the disease course. Most affected individuals remain ambulatory without assistance for decades. Life span appears to be normal.

Genotype-Phenotype Correlations

Only limited genotype-phenotype correlations have been identified. Individuals with biallelic loss-of-function variants have been reported to use walking aids at a significantly earlier age than individuals with pathogenic variants that are expected to lead to partial or reduced function. Individuals homozygous for ANO5 pathogenic variant c.2272C>T (p.Arg758Cys) showed a significantly later use of walking aids compared to individuals with other ANO5 pathogenic variants [de Bruyn et al 2023].

Nomenclature

LGMD-R12 was previously referred to as LGMD2L [Straub et al 2018].

MMD3 may also be referred to as non-dysferlin Miyoshi muscular dystrophy.

Prevalence

ANO5-related muscle disease has been estimated to be one of the most common causes of limb-girdle muscular dystrophy. Prevalence in Finland is as high as 2:100,000 [Penttilä et al 2012]; in the north of England it has been estimated at 0.26:100,000 [Hicks et al 2011]. In Europe, ANO5-related muscle disease has been estimated to be the third most prevalent LGMD subtype (26%), although this may be an underestimation due to the less severe phenotype [Ten Dam et al 2019]. In a large cohort study of 4,656 individuals with clinically suspected LGMD across the United States, ANO5 was the fourth most prevalent LGMD subtype (7%) [Nallamilli et al 2018].

The most frequent ANO5 pathogenic variant, c.191dupA (p.Asn64LysfsTer15), is found in more that 50% of affected individuals of European ancestry [de Bruyn et al 2023]. In Finland, the most common pathogenic variant is c.2272C>T (p.Arg758Cys) [Penttilä et al 2012]; in the Netherlands, c.1898+1G>A (p.Met470LeufsTer16) has been reported to be more common than c.191dupA [Ten Dam et al 2019].

Evaluations Following Initial Diagnosis

To establish the extent of disease and needs of an individual diagnosed with ANO5-related muscle disease, the evaluations summarized in Table 3 (if not performed as part of the evaluation that led to the diagnosis) are recommended.

Treatment of Manifestations

No definitive treatments for the limb-girdle muscular dystrophies exist. Management is tailored to each individual and each specific subtype.

Surveillance

To monitor existing manifestations, the individual's response to supportive care, and the emergence of new manifestations, the evaluations summarized in Table 5 are recommended.

Agents/Circumstances to Avoid

Heavy muscle force training of weak muscles should be avoided, as very high plasma CK concentration has been measured after strenuous exercise [Milone et al 2012, Penttilä et al 2012].

The use of statins, which can induce muscle pain and worsen muscle weakness, should be avoided. If absolutely necessary for the health of the individual, statin use requires extra monitoring of clinical status, especially at the beginning of treatment.

Evaluation of Relatives at Risk

See Genetic Counseling for issues related to testing of at-risk relatives for genetic counseling purposes.

Therapies Under Investigation

Search ClinicalTrials.gov in the US and EU Clinical Trials Register in Europe for access to information on clinical studies for a wide range of diseases and conditions. Note: There may not be clinical trials for this disorder.

Mode of Inheritance

ANO5-related muscle disease is inherited in an autosomal recessive manner.

Risk to Family Members

Parents of a proband

• The parents of an affected individual are presumed to be heterozygous for an ANO5 pathogenic variant.
• Molecular genetic testing is recommended for the parents of a proband to confirm that both parents are heterozygous for an ANO5 pathogenic variant and to allow reliable recurrence risk assessment.
• If a pathogenic variant is detected in only one parent and parental identity testing has confirmed biological maternity and paternity, it is possible that one of the pathogenic variants identified in the proband occurred as a de novo event in the proband or as a postzygotic de novo event in a mosaic parent [Jónsson et al 2017]. If the proband appears to have homozygous pathogenic variants (i.e., the same two pathogenic variants), additional possibilities to consider include:
  • A single- or multiexon deletion in the proband that was not detected by sequence analysis and that resulted in the artifactual appearance of homozygosity;
  • Uniparental isodisomy for the parental chromosome with the pathogenic variant that resulted in homozygosity for the pathogenic variant in the proband.
• Heterozygous parents of an individual with ANO5-related muscle disease are asymptomatic and are not at risk of developing an ANO5-related muscle disease.

Sibs of a proband

• If both parents are known to be heterozygous for an ANO5 pathogenic variant, each sib of an affected individual has at conception a 25% chance of being affected, a 50% chance of being an asymptomatic carrier, and a 25% chance of being unaffected and not a carrier.
• Individuals with the same pathogenic variants can develop different phenotypes even within the same family, including limb-girdle muscular dystrophy R12 anoctamin-5-related (LGMD-R12), Miyoshi muscular dystrophy 3 (MMD3), and asymptomatic hyperCKemia. Females tend to have milder disease manifestations than males with the same ANO5 pathogenic variants [de Bruyn et al 2023].
• Heterozygous sibs of an individual with ANO5-related muscle disease are asymptomatic and are not at risk of developing an ANO5-related muscle disease.

Offspring of a proband. Unless an affected individual's reproductive partner also has an ANO5-related muscle disease or is a carrier, offspring will be obligate heterozygotes (carriers) for a pathogenic variant in ANO5.

Other family members. Each sib of the proband’s parents is at a 50% risk of being a carrier.

Carrier Detection

Carrier testing for at-risk relatives requires prior identification of the ANO5 pathogenic variants in the family.

Related Genetic Counseling Issues

Family planning

• The optimal time for determination of genetic risk and discussion of the availability of prenatal/preimplantation genetic testing is before pregnancy.
• It is appropriate to offer genetic counseling (including discussion of potential risks to offspring and reproductive options) to young adults who are affected, are carriers, or are at risk of being carriers.
• Carrier testing should be considered for the reproductive partners of known carriers and for the reproductive partners of individuals affected with ANO5-related muscle disease, particularly if both partners are of the same ancestry. A founder variant has been identified in the Dutch population (see Table 6).

Prenatal Testing and Preimplantation Genetic Testing

Once the ANO5 pathogenic variants have been identified in an affected family member, prenatal and preimplantation genetic testing are possible.

Differences in perspective may exist among medical professionals and within families regarding the use of prenatal and preimplantation genetic testing. While most health care professionals would consider use of prenatal and preimplantation genetic testing to be a personal decision, discussion of these issues may be helpful.

Molecular Pathogenesis

ANO5 encodes anoctamin-5, which belongs to a protein family of Ca²⁺-activated ion channels and phospholipid scramblases. Not much is known about its normal function, and the molecular pathogenesis is so far not understood. According to one study, anoctamin-5 deficiency compromises the plasma membrane repair ability of myoblasts [Chandra et al 2019].

Mechanism of disease causation. Likely loss of function. This is based on the observation that in most individuals, regardless of the type of pathogenic variant (truncating or missense), anoctamin-5 is clearly reduced in muscle biopsies.

ANO5-specific laboratory technical considerations

• A Western blotting method has been developed to detect endogenous anoctamin-5 in membrane fractions extracted from human muscle biopsies. This method can be used to quantify the anoctamin-5 protein and evaluate the pathogenicity of novel ANO5 variants of uncertain significance.
• For ClinGen variant interpretation guidelines, see ClinGen Limb Girdle Muscular Dystrophy Expert Panel Specifications to the ACMG/AMP Variant Interpretation Guidelines for ANO5 Version 2.0.0.

Author History

Manu Jokela, MD, PhD (2025-present)
Johanna Palmio, MD, PhD (2012-present)
Sini Penttilä, PhD (2012-present)
Bjarne Udd, MD, PhD; University Hospital Tampere, Finland (2012-2025)
Anna Vihola, PhD; Fimlab Laboratories (2019-2025)

Revision History

• 15 May 2025 (sw) Comprehensive update posted live
• 22 August 2019 (ha) Comprehensive update posted live
• 29 November 2012 (me) Review posted live
• 19 July 2012 (sp) Original submission

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