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PubMed This is a summary of 19 peer-reviewed journal articles Updated
Medical Genetics

The Diagnostic Journey: Genetics vs. Biopsy

At a Glance

Genetic testing using Next-Generation Sequencing is now the primary method for diagnosing congenital myopathy, replacing the muscle biopsy as the first-line choice. However, a biopsy may still be necessary if genetic results are unclear or reveal a Variant of Uncertain Significance.

For many years, the only way to diagnose a muscle disease was to perform an invasive muscle biopsy—surgically removing a small piece of muscle to look at it under a microscope. Today, the “diagnostic journey” has fundamentally changed. Next-Generation Sequencing (NGS) is now the first-line gold standard for confirming a congenital myopathy [1][2][3].

What is Genetic Testing?

Think of your child’s DNA as a massive library of instruction manuals. Genetic testing is like a high-tech search engine that scans those manuals for “spelling errors.”

  • Targeted Panels: These look at a specific group of genes (usually 50 to 100) known to cause muscle disease.
  • Whole Exome Sequencing (WES): This scans every gene in the body that provides instructions for building proteins. It is often used when a standard panel doesn’t find an answer [4][5]. Note that WES can sometimes reveal “incidental findings” (genetic risks for completely unrelated health conditions), so genetic counseling before testing is highly recommended.

Why Genetics is Primary

A genetic diagnosis is the “gold standard” because it identifies the cause of the condition, not just the result. It can guide everything from what to expect in the future (prognosis) to which medicines are safe and which clinical trials your child can join [6][7][8].

The Role of the Muscle Biopsy

While genetic testing is the first choice, the muscle biopsy is not obsolete. It remains a vital “back-up” tool in specific situations:

  1. Ambiguity: If genetic testing finds a “suspicious” change but the doctors aren’t sure if it’s the cause [9][10].
  2. Negative Results: If genetic tests come back normal but the child clearly has muscle weakness [11][12].
  3. Validation: To see if the structural defects in the muscle (like rods or cores) “match” the genetic blueprint found in the testing [9].

Diagnostic Pitfalls: The VUS and Inheritance

One of the most common challenges in modern testing is the Variant of Uncertain Significance (VUS). This means the lab found a “spelling change” in a gene, but they don’t have enough scientific data yet to say if it causes disease or if it’s just a normal human variation [9][13].

Additionally, many congenital myopathies are autosomal recessive. This means a child must inherit two mutated copies of a gene (one from each parent) to have the disease. If a report only finds one “pathogenic” error on a recessive gene, the diagnosis is not yet fully confirmed [14]. In these cases, your doctor may suggest “trio testing” (testing both parents) or a muscle biopsy to help clarify the result [15][16].

Your Diagnostic “Completeness Checklist”

To ensure your child’s report provides the information needed for modern care and clinical trial readiness, it should contain these three critical data points:

Checkpoint What to Look For Why it Matters
Gene Name e.g., RYR1, NEB, ACTA1 Tells you exactly which protein is affected [17].
Inheritance Pattern e.g., Autosomal Recessive Explains the risk for siblings or future children [14].
Variant Classification Pathogenic or Likely Pathogenic Confirms that the lab is confident this is the cause [18][19].

If your child’s report only lists a “Variant of Uncertain Significance (VUS),” the diagnosis may not yet be considered “definitive,” and more follow-up may be required [13][10].

Common questions in this guide

Is a muscle biopsy required to diagnose congenital myopathy?
In many cases, a muscle biopsy is no longer the first step. Next-Generation Sequencing genetic testing is now the gold standard for diagnosis. However, a biopsy may still be necessary if genetic test results are negative or unclear.
What does a Variant of Uncertain Significance (VUS) mean on my child's report?
A Variant of Uncertain Significance means the laboratory found a change in your child's DNA, but there is not enough scientific evidence yet to confirm if it causes the muscle disease. Your doctor may suggest testing both parents or performing a muscle biopsy to clarify the result.
What is the difference between a targeted gene panel and Whole Exome Sequencing?
A targeted panel looks specifically at a known group of genes that cause muscle disease, usually 50 to 100 genes. Whole Exome Sequencing scans all the genes in the body that provide instructions for making proteins, which is helpful when standard panels fail to find a cause.
What specific details need to be on a complete genetic report for congenital myopathy?
To ensure clinical trial readiness, a complete report should list the specific gene name affected, the inheritance pattern, and a variant classification of either pathogenic or likely pathogenic.

Questions to Ask Your Doctor

Curated prompts to bring to your next appointment.

  1. 1.Was my child’s testing done through a targeted 'myopathy panel' or 'Whole Exome Sequencing' (WES)?
  2. 2.If a VUS (Variant of Uncertain Significance) was found, would a muscle biopsy help us confirm if that variant is actually the cause?
  3. 3.Does the laboratory report specify if this was a 'de novo' mutation or if it was inherited from one of us?
  4. 4.Now that we have this specific genetic result, are there any gene-specific clinical trials my child might qualify for?
  5. 5.How often do you revisit genetic reports to see if any VUS classifications have been updated as more research is published?

Questions For You

Tap a prompt to share your answer — we'll use it plus this page's context to start a tailored conversation.

References

References (19)
  1. 1

    Biallelic LINE insertion mutation in HACD1 causing congenital myopathy.

    Al Amrani F, Gorodetsky C, Hazrati LN, et al.

    Neurology. Genetics 2020; (6(3)):e423 doi:10.1212/NXG.0000000000000423.

    PMID: 32426512
  2. 2

    Congenital myopathies.

    Younger DS

    Handbook of clinical neurology 2023; (195()):533-561 doi:10.1016/B978-0-323-98818-6.00027-3.

    PMID: 37562885
  3. 3

    Application of whole exome sequencing in the diagnosis of muscular disorders: a study of Taiwanese pediatric patients.

    Lee CL, Chuang CK, Chiu HC, et al.

    Frontiers in genetics 2024; (15()):1365729 doi:10.3389/fgene.2024.1365729.

    PMID: 38818036
  4. 4

    The genetic basis of undiagnosed muscular dystrophies and myopathies: Results from 504 patients.

    Savarese M, Di Fruscio G, Torella A, et al.

    Neurology 2016; (87(1)):71-6 doi:10.1212/WNL.0000000000002800.

    PMID: 27281536
  5. 5

    [The MYOCAPTURE project: Capturing the elusive mutations behind congenital myopathies].

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    Medecine sciences : M/S 2025; (41 Hors série n° 2()):64-70 doi:10.1051/medsci/2025180.

    PMID: 41313064
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    Exome sequencing in undiagnosed congenital myopathy reveals new genes and refines genes-phenotypes correlations.

    de Feraudy Y, Vandroux M, Romero NB, et al.

    Genome medicine 2024; (16(1)):87 doi:10.1186/s13073-024-01353-0.

    PMID: 38982518
  7. 7

    Fundoscopy-directed genetic testing to re-evaluate negative whole exome sequencing results.

    Cho A, Lima de Carvalho JR, Tanaka AJ, et al.

    Orphanet journal of rare diseases 2020; (15(1)):32 doi:10.1186/s13023-020-1312-1.

    PMID: 32000842
  8. 8

    Diagnostic and clinical utility of genetic testing in children with kidney failure.

    Chen J, Lin F, Zhai Y, et al.

    Pediatric nephrology (Berlin, Germany) 2021; (36(11)):3653-3662 doi:10.1007/s00467-021-05141-5.

    PMID: 34031707
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    Myopathology in congenital myopathies.

    Sewry CA, Wallgren-Pettersson C

    Neuropathology and applied neurobiology 2017; (43(1)):5-23 doi:10.1111/nan.12369.

    PMID: 27976420
  10. 10

    One case of congenital myopathy caused by new mutation of RYR1 gene and literature review.

    Deng Q, Ding Z, Fu Q, Lin M

    Gene 2023; (876()):147493 doi:10.1016/j.gene.2023.147493.

    PMID: 37207825
  11. 11

    Coexistence of central nucleus, cores, and rods: Diagnostic relevance.

    Dhinakaran S, Kumar RS, Thakkar R, Narayanappa G

    Annals of Indian Academy of Neurology 2016; (19(2)):201-4 doi:10.4103/0972-2327.176861.

    PMID: 27293330
  12. 12

    A recurrent RYR1 mutation associated with early-onset hypotonia and benign disease course.

    Biancalana V, Rendu J, Chaussenot A, et al.

    Acta neuropathologica communications 2021; (9(1)):155 doi:10.1186/s40478-021-01254-y.

    PMID: 34535181
  13. 13

    Congenital myopathies: an update.

    Claeys KG

    Developmental medicine and child neurology 2020; (62(3)):297-302 doi:10.1111/dmcn.14365.

    PMID: 31578728
  14. 14

    A Study of a Cohort of X-Linked Myotubular Myopathy at the Clinical, Histologic, and Genetic Levels.

    Abath Neto O, Silva MR, Martins Cde A, et al.

    Pediatric neurology 2016; (58()):107-12.

    PMID: 26995067
  15. 15

    A Phenotype-Enhanced Variant Classification Framework to Decrease the Burden of Variants of Uncertain Significance in Type 2 Long QT Syndrome.

    Neves R, Crotti L, Bains S, et al.

    JACC. Clinical electrophysiology 2026; (12(2)):350-359 doi:10.1016/j.jacep.2025.10.005.

    PMID: 41288544
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    Investigating the frequency of unreported cases and laboratory correspondence practices for variants of uncertain significance in pediatric epilepsy.

    Vilaboy T, Wong K, Tristani-Firouzi M, et al.

    Epilepsia open 2025; (10(5)):1726-1732 doi:10.1002/epi4.70132.

    PMID: 40857170
  17. 17

    Clinical validity of congenital myopathy genes determined by the ClinGen Congenital Myopathies Expert Panel.

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    Journal of neuromuscular diseases 2025; (12(6)):778-792 doi:10.1177/22143602251339369.

    PMID: 40491337
  18. 18

    Navigating the nuances of clinical sequence variant interpretation in Mendelian disease.

    Strande NT, Brnich SE, Roman TS, Berg JS

    Genetics in medicine : official journal of the American College of Medical Genetics 2018; (20(9)):918-926 doi:10.1038/s41436-018-0100-y.

    PMID: 29988079
  19. 19

    Performance of ACMG-AMP Variant-Interpretation Guidelines among Nine Laboratories in the Clinical Sequencing Exploratory Research Consortium.

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    PMID: 27181684

This page provides educational information about diagnosing congenital myopathy and reading genetic test reports. It does not replace professional medical advice from your child's neurologist, genetic counselor, or healthcare team.

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