Which states have a higher incidence of malignant hyperthermia?

October 2, 2025 •

5 min read

While malignant hyperthermia (MH) is a rare and life-threatening condition, certain geographical areas have reported a higher concentration of susceptible families. This article explores which states have a higher incidence of malignant hyperthermia and the factors contributing to these regional variations.

Quick Summary

Areas with a higher incidence of malignant hyperthermia include Wisconsin and other states in the Upper Midwest, such as Michigan, Nebraska, and West Virginia, likely due to ancestral genetic factors within concentrated populations.

Key Points

Geographical Hotspots: States in the Upper Midwest, such as Wisconsin and Michigan, and others like Nebraska and West Virginia, have reported higher concentrations of malignant hyperthermia cases.
Genetic Factors: This regional clustering is primarily due to the hereditary nature of malignant hyperthermia, where ancestral gene mutations can become concentrated within certain populations over time.
Reporting Challenges: The true incidence of malignant hyperthermia is not known with certainty, partly due to the lack of universal reporting and inconsistencies in data collection across states and hospitals.
Family History is Key: Your personal or family history is a more significant risk factor for malignant hyperthermia than your geographical location. A family history of MH necessitates a conversation with your doctor.
Modest Variations: Studies comparing hospital discharge data from different states show only modest variations in reported malignant hyperthermia diagnoses, highlighting that anecdotal hotspots may not reflect absolute genetic prevalence.
Seek Medical Guidance: If you have a family history of malignant hyperthermia, it is crucial to inform your medical team before any surgery involving anesthesia and consider genetic testing.

Understanding Malignant Hyperthermia

Malignant hyperthermia (MH) is a rare, inherited pharmacogenetic disorder of skeletal muscle. It is most often triggered by certain inhaled anesthetic gases and the muscle relaxant succinylcholine during surgery. The condition causes a hypermetabolic reaction in susceptible individuals, characterized by a rapid increase in body temperature, severe muscle rigidity, and other life-threatening symptoms. While MH can affect individuals worldwide, the incidence appears to be higher in certain geographical regions due to specific population demographics.

The Role of Genetics in Geographical Incidence

The inheritance pattern of MH is autosomal dominant, meaning only one parent needs to carry the mutated gene for a child to have a 50% chance of inheriting the susceptibility. The most common genetic mutation linked to MH occurs in the RYR1 gene, which controls the calcium release channel in muscle cells. Variations in this gene can lead to an uncontrolled release of calcium, causing the hypermetabolic state.

The reason for regional differences in MH incidence is often rooted in the founder effect. This genetic phenomenon occurs when a new population is established by a small number of individuals who carry specific genetic traits. If one of these founders carries the MH-susceptibility gene, it can become more prevalent within that population over generations. For example, populations of Northern European descent, particularly those with Scandinavian, German, and Czech ancestry who settled in certain parts of the United States, have shown higher rates of MH.

Documented High-Incidence Areas in the U.S.

Several states have been anecdotally or formally noted for having higher concentrations of MH-susceptible families. Health professionals and organizations like the Malignant Hyperthermia Association of the United States (MHAUS) monitor and report these regional patterns. Based on historical data and anecdotal reports, the following areas have been identified as having a higher incidence:

Wisconsin and the Upper Midwest: Often cited as a primary MH "hotspot," Wisconsin has a well-documented concentration of MH-susceptible families. This is particularly true for regions with large populations of Northern European ancestry.
Michigan: Adjacent to Wisconsin, Michigan is also frequently mentioned as a state with a higher MH incidence. The genetic links within certain populations likely contribute to this regional clustering.
Nebraska: Similar to other Midwestern states with large ancestral populations from Europe, Nebraska has been noted as a high-incidence area.
West Virginia: Another state on the list of high-incidence areas, West Virginia's higher rate could be linked to founder effects within historical populations.

It is important to remember that MH is still a rare event on a national scale, and the precise incidence is difficult to determine due to a lack of universal reporting. However, these concentrated areas highlight the hereditary nature of the disorder.

Factors Influencing Reported Incidence

Reported incidence numbers for MH are notoriously complex to track accurately. Several factors can influence why one state might report a higher rate than another, even if the underlying genetic prevalence is similar. The following elements play a significant role:

Reporting Practices: The consistency and thoroughness of reporting MH crises to the North American Malignant Hyperthermia Registry vary by state and hospital. Areas with greater awareness and more robust reporting protocols may appear to have higher rates simply because they are better at documenting cases.
Population Density and Demographics: The concentration of populations with specific genetic backgrounds in certain states is a key driver. States with large populations descended from European immigrants, for example, may see higher prevalence rates.
Awareness and Training: Regions with medical facilities that have a high awareness of MH due to previous cases or specialized training may be more likely to correctly diagnose and report a reaction. In contrast, in areas with low awareness, an MH episode might be misdiagnosed or attributed to another cause.
Surgical Procedures: The use of triggering anesthetic agents can also influence reported numbers. In some areas, shifts in anesthetic practices may affect the number of triggered reactions, but this is less likely to influence the overall underlying genetic prevalence.

Comparison of MH Prevalence Reporting

To illustrate the geographical variation, here is a comparison of reported MH prevalence per 100,000 hospital discharges based on a study examining data from 2011/2012. While this data is over a decade old and reflects diagnoses rather than true genetic prevalence, it highlights regional differences observed in clinical settings.


State	MH Prevalence (per 100,000 hospital discharges)	Potential Contributing Factors
California	1.91	Large, diverse population; potential for higher overall case numbers.
Florida	1.80	High population density; anecdotal evidence of excess risk.
Wisconsin	1.60	Historical concentrations of MH-susceptible families.
New York	1.23	Large, diverse population; reporting variations.

It is crucial to note that this comparison is a snapshot in time and does not represent the full picture of genetic prevalence. The modest variation suggests that while clustering exists, the reporting of clinical MH diagnoses can be influenced by multiple factors beyond pure geography.

What to Do if You Live in a High-Incidence State

For most individuals, living in a high-incidence state for MH does not significantly change their overall risk, which remains very low. The primary risk factor is a family history of the disorder. If you have a relative who has been diagnosed as MH susceptible, regardless of your location, you should take precautions.

Here are some proactive steps to take:

Inform your medical providers: Always inform your anesthesiologist and surgeon about your family history of MH before any procedure involving anesthesia.
Wear a medical alert bracelet: This can alert first responders to your condition in an emergency.
Register with MHAUS: The Malignant Hyperthermia Association of the United States provides a registry and educational materials for MH-susceptible individuals and their families. Their website is an authoritative source of information and support: https://www.mhaus.org/
Consider genetic counseling: If you have a strong family history, a genetic counselor can help you understand your risk and the options for genetic testing.

Conclusion

While malignant hyperthermia is a rare disorder, some states like Wisconsin, Michigan, Nebraska, and West Virginia have historically been associated with a higher incidence due to the concentration of certain genetic traits within ancestral populations. However, the exact prevalence is difficult to determine with certainty due to underreporting and the influence of other factors. The most important determinant of risk is personal or family history, not geography. Proactive communication with your medical team and understanding your family's medical background are the best ways to manage this inheritable condition, regardless of where you live.

Frequently Asked Questions

Not necessarily. The most important risk factor for malignant hyperthermia is having a family history of the disorder. Living in a state with a higher documented incidence, like Wisconsin or Michigan, does not significantly increase the risk for the general population, as the higher rates are due to clusters within specific families and ancestral populations.

The higher incidence in certain states, particularly in the Upper Midwest, is believed to be a result of the 'founder effect'. Historical populations with specific genetic backgrounds, such as those of Northern European descent who carry the MH-susceptibility gene, settled in these areas, causing the trait to become more concentrated within the local population over generations.

Based on historical reports and data, states including Wisconsin, Michigan, Nebraska, and West Virginia have been identified as having higher regional concentrations of malignant hyperthermia cases.

While it is most often triggered by specific inhalational anesthetics and succinylcholine, rare cases of malignant hyperthermia-like reactions have been reported in susceptible individuals due to other stressors like vigorous exercise or heat.

Yes, genetic testing is available to determine susceptibility to malignant hyperthermia. It typically involves analyzing DNA for mutations in genes like RYR1. The Malignant Hyperthermia Association of the United States (MHAUS) can provide information on genetic testing facilities.

If you have a family history of malignant hyperthermia, you should inform all your medical providers, especially anesthesiologists and surgeons, of your susceptibility before any procedure requiring anesthesia. You can also wear a medical alert bracelet and register with MHAUS.

The exact overall incidence is unknown due to underreporting, but estimates suggest it occurs in about 1 in 100,000 adult anesthetics and 1 in 30,000 pediatric anesthetics. However, the genetic prevalence of MH susceptibility is thought to be much higher, possibly affecting 1 in 2,000 to 3,000 individuals.