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Malignant Hyperthermia

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Overview

What is malignant hyperthermia? The following text is taken from the Genetics Home Reference (update pending):

Malignant hyperthermia is a severe reaction to particular drugs that are often used during surgery and other invasive procedures. Specifically, this reaction occurs in response to some anesthetic gases, which are used to block the sensation of pain, and with a muscle relaxant that is used to temporarily paralyze a person during a surgical procedure. If given these drugs, people at risk for malignant hyperthermia may experience muscle rigidity, breakdown of muscle fibers (rhabdomyolysis), a high fever, increased acid levels in the blood and other tissues (acidosis), and a rapid heart rate. Without prompt treatment, the complications of malignant hyperthermia can be life-threatening.

People at increased risk for this disorder are said to have malignant hyperthermia susceptibility. Affected individuals may never know they have the condition unless they undergo testing or have a severe reaction to anesthesia during a surgical procedure. While this condition often occurs in people without other serious medical problems, certain inherited muscle diseases (including central core disease and multiminicore disease) are associated with malignant hyperthermia susceptibility.

Frequency
Malignant hyperthermia occurs in 1 in 5,000 to 50,000 instances in which people are given anesthetic gases. Susceptibility to malignant hyperthermia is probably more frequent, because many people with an increased risk of this condition are never exposed to drugs that trigger a reaction.

Causes
Variations of the CACNA1S and RYR1 genes increase the risk of developing malignant hyperthermia.

Researchers have described at least six forms of malignant hyperthermia susceptibility, which are caused by mutations in different genes. Mutations in the RYR1 gene are responsible for a form of the condition known as MHS1. These mutations account for most cases of malignant hyperthermia susceptibility. Another form of the condition, MHS5, results from mutations in the CACNA1S gene. These mutations are less common, causing less than 1 percent of all cases of malignant hyperthermia susceptibility.

The RYR1 and CACNA1S genes provide instructions for making proteins that play essential roles in muscles used for movement (skeletal muscles). For the body to move normally, these muscles must tense (contract) and relax in a coordinated way. Muscle contractions are triggered by the flow of certain charged atoms (ions) into muscle cells. The proteins produced from the RYR1 and CACNA1S genes are involved in the movement of calcium ions within muscle cells. In response to certain signals, the CACNA1S protein helps activate the RYR1 channel, which releases stored calcium ions within muscle cells. The resulting increase in calcium ion concentration inside muscle cells stimulates muscle fibers to contract.

Mutations in the RYR1 or CACNA1S gene cause the RYR1 channel to open more easily and close more slowly in response to certain drugs. As a result, large amounts of calcium ions are released from storage within muscle cells. An overabundance of available calcium ions causes skeletal muscles to contract abnormally, which leads to muscle rigidity in people with malignant hyperthermia. An increase in calcium ion concentration within muscle cells also activates processes that generate heat (leading to increased body temperature) and produce excess acid (leading to acidosis).

The genetic causes of several other types of malignant hyperthermia (MHS2, MHS4, and MHS6) are still under study. A form of the condition known as MHS3 has been linked to the CACNA2D1 gene. This gene provides instructions for making a protein that plays an essential role in activating the RYR1 channel to release calcium ions into muscle cells. Although this gene is thought to be related to malignant hyperthermia in a few families, no causative mutations have been identified.

Inheritance Pattern
Malignant hyperthermia susceptibility is inherited in an autosomal dominant pattern, which means one copy of the altered gene in each cell is sufficient to increase the risk of a severe reaction to certain drugs used during surgery. In most cases, an affected person inherits the altered gene from a parent who is also at risk for the condition.

Resources

We are compiling a list of websites to help you understand genetics and genetic test results. If you would like to suggest other resources for this section, please feel free to This email address is being protected from spambots. You need JavaScript enabled to view it.!
INFORMATION ABOUT GENETICS AND GENETIC TESTING:

Weblink to Genetics Home Reference Genetics Home Reference
Consumer-friendly information about the effects of genetic variations on human health. Federally-supported resources, include reviews of more than 800 genetic diseases and more than 1000 genes.


Weblink to NHGRI Learning ResourcesLearning Resources from the NHGRI
Lots of very good resources from the NHGRI, including major sections about The Human Genome Project, Facts Sheets, and educational resources for teachers and students.


Weblink to National Society of Genetic CounselorsFind a Genetic Counselor
The National Society of Genetic Counselors have a searchable database of genetic counselors. Their website also includes some education materials for patients and healthcare professionals.


Weblink to NHGRI Talking GlossaryNHGRI Talking Glossary
Talking glossary of genetic terms developed by the National Human Genome Research Institute. A huge range of definitions is provided by researchers from around the world.


Weblink to Help Me Understand GeneticsHelp Me Understand Genetics
Help Me Understand Genetics is a handbook from the National Institutes of Health that contain useful information about genetics in clear language and provides links to even more online resources. The entire handbook can also be downloaded as a pdf.


Weblink to the Genetic and Rare Diseases Information CenterGenetic and Rare Diseases Information Center (GARD)
A joint project from The Office of Rare Diseases Research (ORDR) and the National Human Genome Research Institute (NHGRI) that provides searchable information about genetic conditions and rare diseases. It also includes a list of FDA-Approved drugs and other medical products for treating rare disease.


Weblink to NORDNational Organization for Rare Disorders - Resources for Parents/Families
The National Organization for Rare Disorders (NORD) is a volunteer organization dedicated to empowering the rare disease community. Again, they have some very nice web resources.


Weblink to ELSIEthical, Legal and Social Implications Research Program
The ELSI Research Program supports examinations and investigations of the ethical, legal and social implications of genetics research.


Weblink to GINAGenetic Information Nondiscrimination Act of 2008
The Genetic Information Nondiscrimination Act of 2008, also referred to as GINA, is a new federal law that protects Americans from being treated unfairly because of differences in their DNA that may affect their health.


Weblink to Learn.GeneticsLearn.Genetics, University of Utah
Excellent resources, especially for those involved in education. Includes a catalog of animations, videos, interactive features, and virtual labs.


Weblink to the Dolan DNA Learning CenterDolan DNA Leaning Center
The DNALC provides genetics learning resources for teachers and students.


INFORMATION FOR RESEARCHERS:

Weblink to the ClinVar ACMG recommendations pageClinVar: ACMG Recommendations for Reporting of Incidental Findings in Clinical Exome and Genome Sequencing
Clinvar's dedicated ACMG page - a useful jumping-off point to the Genetic Testing Registry, OMIM, MedGen, and local ClinVar pages for each gene.


Weblink to NCBI GeneReviews General pageGene Reviews
Gene Reviews (updated September, 2018)


About

What is the purpose of this information?
Our aim is to provide information about why we do genetic testing. We try to answer some common questions and offer guidance on some personal and practical issues. This information is for anybody with questions about genetic testing for any of the diseases and drugs listed in this site.

Are there geographical differences in testing, service or treatment?
Different centers have different policies in terms of how tests are administered and results shared. However, the results discussed in this document should be relevant to most individuals tested for risk of developing genetic disease.

How is this paid for?
If you received this test as part of the eMERGE research study, neither you nor your insurance company will have to pay anything toward this test

When was this content last updated?
October 10, 2018.

More Questions? The National Society of Genetic Counselors has developed a directory to help locate genetic counseling services near you.
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