Normal Function

The CNBP gene provides instructions for making a protein called CCHC-type zinc finger nucleic acid binding protein. This protein has seven regions, called zinc finger domains, which are thought to attach (bind) to specific sites on DNA and its chemical cousin, RNA.

The CNBP protein is found in many of the body's tissues, but it is most abundant in the heart and in muscles used for movement (skeletal muscles). The CNBP protein regulates the activity of other genes and is necessary for normal development before birth, particularly of muscles.

One region of the CNBP gene contains a segment of four DNA building blocks (nucleotides) that is repeated multiple times. This sequence, which is written as CCTG, is called a tetranucleotide repeat. In most people, the CCTG sequence is repeated fewer than 26 times.

Health Conditions Related to Genetic Changes

Myotonic dystrophy

Mutations in the CNBP gene cause a form of myotonic dystrophy known as myotonic dystrophy type 2. Myotonic dystrophy is characterized by progressive muscle wasting and weakness. Muscle weakness in type 2 primarily involves muscles close to the center of the body (proximal muscles), such as the those of the neck, shoulders, elbows, and hips. People with this disorder often have prolonged muscle contractions (myotonia) and are not able to relax certain muscles after use.

The type of gene mutation that causes myotonic dystrophy type 2 is known as a tetranucleotide repeat expansion. This mutation increases the size of the repeated CCTG segment in the CNBP gene. People with myotonic dystrophy type 2 have from 75 to more than 11,000 CCTG repeats.

The mutated CNBP gene produces an altered version of messenger RNA, which is a molecular blueprint of the gene that guides the production of proteins. Researchers have found that the altered messenger RNA traps proteins to form clumps within the cell. The clumps interfere with the production of many other proteins. These changes prevent muscle cells and cells in other tissues from functioning properly, leading to muscle weakness and the other features of myotonic dystrophy type 2.

Other Names for This Gene

• CCHC-type zinc finger, nucleic acid binding protein
• cellular nucleic acid binding protein
• cellular retroviral nucleic acid-binding protein 1
• CNBP1
• CNBP_HUMAN
• DM2
• ZCCHC22
• zinc finger 9 protein
• zinc finger protein 273
• zinc finger protein 9
• zinc finger protein 9 (a cellular retroviral nucleic acid binding protein)
• ZNF9

Genomic Location

There is currently no treatment available to stop or slow the progression of myotonic dystrophy type 2. Management options depend on the symptoms that each affected person has, and aim to treat each specific symptom. For example:

• Ankle-foot braces, wheelchairs, or other assistive devices may be used as needed for weakness
• Defibrillator placement may be needed for arrhythmias
• Cataracts can be removed for those with impaired vision
• Testosterone replacement therapy may be useful for hypogonadism in males

Myotonia is usually mild and rarely requires treatment. Routine exercise appears to help with pain control, as well as with muscle strength and endurance. The effectiveness of most medications for pain management varies. Mexilitene, which is very effective for some forms of myotonia, has helped control muscle pain in some people with this condition. Other medications that have been used with some success include gabapentin, nonsteroidal anti-inflammatory drugs (NSAIDS), low-dose thyroid replacement, low-dose steroids, and tricyclic antidepressants. Cholesterol-lowering medications should be avoided when they are associated with increased weakness.

There are steps a person can take to prevent some secondary complications. Anesthetic risk may be increased, so careful assessment of heart and respiratory function before and after surgery are recommended. Affected people should also have a yearly electrocardiogram or cardiac MRI to detect possible conduction defects or cardiomyopathy.