PatientCrossroads CMD


Glossary of Terms Related to Congenital Muscle Disease

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Term Definition
Germline Mutation

A mutation in one or more but not all of the cells that the body will use to produce egg and sperm cells. Usually this mutation is not present in other cells of the individual and cannot be detected with a blood test.


Hypotonic or hypotonia means having less than normal tone or tension. Children with CMD are often hypotonic at, or shortly after, birth.


The staining of a specific substance, such as muscle tissue, to identify and visualize the tissue

Inframe Mutation

A mutation that does not cause a shift in the triplet reading frame; such mutations can, however, lead to an abnormal protein product

Insertion Mutation

DNA is the genetic language and is read from left to right in 3 letter words. Let us say a normal piece of DNA says “THE MAN HAS CAT AND HAT” . DNA language does not have spaces so in DNA language, above would read: THEMANHASCATANDHAT. In an insertion, one or more letters are inserted. If two letters BX and were inserted after MAN, reading the genetic language in DNA would not make sense: THE MAN BXH ASC ATA NDH AT.


Genes have both noncoding (introns) and coding (exons) regions. The noncoding regions contain genetic information that gets cut out when the genetic information goes from DNA to RNA and is not integral to protein manufacture. Point mutations in the introns usually have no effect, unless they cause a shift in the reading frame through an insertion or deletion. Exons contain the actual genetic information that will be used to manufacture proteins. Point mutations, insertions, duplications and deletions all are types of mutations that change the genetic code and can lead to disease.

Missense Mutation

A missense mutation is a genetic change involving the substitution of one base in the DNA for another which results in the substitution of one amino acid in a polypeptide for another. A missense mutation is a “readable” genetic message although its “sense” (its meaning) is changed. This is in contrast to a nonsense mutation which has no meaning except to halt the reading of the genetic message.

Muscle Biopsy

A muscle biopsy is a minor surgical procedure done under general or local anesthetic, using a needle or a small incision to remove a small sample of muscle. The procedure may be done to confirm a clinical diagnosis, distinguish between nerve and muscle disorders, identify a metabolic defect of muscle, diagnose diseases of connective tissue and blood vessels, detect muscle inflammation, or rule out muscle disease. Afterwards, there may be minor discomfort and bruising at the biopsy site which usually takes a week to heal fully.


A physician trained to specialize in diseases affecting the nervous system. These diseases include the muscular dystrophies, Lou Gehrigs (ALS), Parkinsons, dementia, stroke and neuropathies. For the first time, this year, the American Academy of Psychiatrists and Neurologists is offering special board certification in the muscle diseases. This is a voluntary certification and would probably indicate a special interest on the part of that physician to pursue further certification. Because the CMD’s are rare diseases, it is possible that your local neurologist will not have seen a child or adult with CMD before. Especially in the early stages of diagnosis, it is important to find a knowledgeable neurologist to guide testing and diagnosis. Contacting the MDA, can be a resource to find a neurologist with expertise in CMD.

Noninvasive Ventilation

Noninvasive ventilation is the delivery of ventilatory support without the need for an invasive artificial airway. Such ventilation has a role in the management of acute or chronic respiratory failure in many patients and may have a role for some patients with heart failure. Noninvasive ventilation can often eliminate the need for intubation or tracheostomy and preserve normal swallowing, speech, and cough mechanisms. There are several types of noninvasive ventilation; including negative pressure ventilation, bilevel positive airway pressure (BIPAP or bilevel ventilator) device, or a continuous positive airway pressure (CPAP) device. The use of noninvasive positive-pressure ventilation (NPPV) in acute hospital settings and at home has been steadily increasing.

Nonsense Mutation (premature stop codon)

A nonsense mutation refers to a point mutation that changes a genetic sequence into a 3 letter code for a stop sign. If a stop sign arises in the middle of a gene because of a mutation, then when the gene encodes first mRNA and then a protein, a truncated or shortened protein will be made. Most of these shortened proteins are not functional and are destroyed by the cell.


Polymerase Chain Reaction: a process that produces millions of copies of a short segment of DNA. PCR is a very common procedure in molecular genetic testing and may be used to: 1) generate a sufficient quantity of DNA to perform a test, or 2) may be a test in and of itself.


A physician trained to specialize in lung diseases. These diseases include breathing problems in muscle disease, asthma and emphysema. A pulmonologist may not be familiar with how best to diagnose and treat an individual with CMD is having breathing problems.

Quantitative PCR

The use of PCR to determine the amount of DNA or RNA in a sample; commonly used to detect deletion and duplication mutations (see PCR)


The frequency with which a test yields a positive result when the individual being tested is actually affected and/or has the gene mutation in question

Skin Biopsy

A procedure where a piece of skin is removed to diagnose an illness. It may also be called punch biopsy. A skin biopsy can be performed in an outpatient medical setting with some local anesthetic to numb the area. Physicians who specialize in genetics or dermatologists usually perform the skin biopsy

During a skin or punch biopsy, the doctor removes a small round piece of skin using a hollow instrument. Stitches are only required if a large sample is taken. To prepare for the test, tell your doctor about all the medications you are currently taking including over the counter medications. You will feel a stinging sensation when the anesthetic is injected. You may feel a little sore in that area for several days thereafter.

Sleep apnea

A condition in which pauses in breathing (an apnea episode) occur during sleep because the airway has become narrowed, blocked, or floppy.

Variant of Unknown Significance (VOUS)

An alteration in the normal sequence of a gene, the significance of which is unclear until further study of the genotype and corresponding phenotype in a sufficiently large population; complete gene sequencing often identifies numerous (sometimes hundreds) allelic variants for a given gene

Western Blot

A molecular genetic technique to separate proteins, by running on a gel, and identification of the proteins by immunological staining techniques

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