HRM curve analysis identifies patients at risk of MH

A new DNA test may make it much simpler to identify patients at risk of malignant hyperthermia (MH)—a rare but life-threatening complication of exposure to common anesthetics reports the November issue of Anesthesia & Analgesia, official journal of the International Anesthesia Research Society (IARS).

The new technique, called high resolution melting (HRM) curve analysis, provides a "sensitive and specific tool" for the identification of genetic variants responsible for MH—and a much simpler alternative to currently available tests. Dr Marcus Broman of Skåne University Hospital Lund, Malmö, Sweden, is lead author of the new study.

HRM Curve Analysis Assesses MH Risk by Measuring DNA 'Melting Point'
Malignant hyperthermia is a rare condition in which genetically susceptible people develop rapid increases in body temperature and muscle rigidity in response to certain anesthetics and other drugs. Once the condition is recognized, it can generally be avoided by substituting other anesthetics. However, susceptible patients generally go unrecognized until they (or a family member) experience an episode of MH.

HRM curve analysis was developed to meet the need for a new test for assessing MH risk. The current test is highly invasive, requiring a biopsy specimen of quadriceps (thigh) muscle and specialized testing equipment. A genetic test would be a valuable alternative, but is impractical because so many different gene variants can cause MH. Many of them occur in a gene called RYR1—the very large size of which makes it difficult to screen for variants.

The new test takes a different approach, using a sample of DNA extracted from a blood sample. Fragments of DNA from the RYR1 gene are identified and gradually heated to assess the temperature at which the strands of DNA begin to unwind. Fragments with unusual, or "aberrant," melting profiles can undergo full gene sequencing to pinpoint specific variants potentially causing MH.

Dr. Broman and colleagues evaluated the HRM curve analysis approach in 16 "MH susceptible" patients. All had either experienced a life-threatening episode of MH themselves, had a close relative who had died of MH, or had undergone the muscle biopsy test for suspected abnormalities. A total of approximately 2,500 DNA fragments underwent HRM curve analysis.

The test showed "significantly aberrant melting profiles" in 21 percent of the DNA fragments tested. Subsequent gene sequencing studies identified 131 variants known to cause MH, along with 17 known or suspected mutations.

Overall, 13 of the 16 MH-susceptible patients had genetic abnormalities known or suspected of causing MH—a rate of 81 percent. Using HRM curve analysis to look for MH-related mutations of the RYR1 gene would greatly reduce the need for in-depth gene sequencing studies, without sacrificing test sensitivity. "This suggests savings of both workload and cost, because technically the sequencing procedure is more laborious and expensive than the HRM procedure," according to Broman and coauthors.

Although it has some limitations, HRM curve analysis is a promising approach to identifying patients at risk of MH, according to an accompanying editorial by Dr Henry Rosenberg of Saint Barnabas Medical Center, Livingston, N.J. He writes, "The study, if confirmed and expanded by others, will greatly enhance the ability to screen a large number of samples of DNA to facilitate further research and eventually diagnostic testing for MH susceptibility."

Dr. Rosenberg foresees a day when powerful genetic tests will be available to test for MH susceptibility in many different genes simultaneously. He also thinks the new findings may be relevant to other muscle diseases as well as heat-related syndromes—many of which are also related to RYR1 gene variants.