A Scottish whaler came ashore in Wellington during the 1840s, later moving to the Manawatū and marrying a woman from the Ōtaki region. The man is considered “genetically successful”, and the family grew quickly over subsequent generations. But in doing so he passed down a gene variant that can be deadly for the carrier under anaesthetic. Those with the gene variant have the disorder malignant hyperthermia (MH), which is otherwise completely harmless.
MH causes the patient to go rigid under conventional anaesthetic, their temperature and heart rate rising. This can quickly lead to fatal cardiac arrest unless they’re given the antidote dantrolene.
In 1968 a 20-year-old died during jaw surgery in Palmerston North Hospital, leading to the discovery of the large Manawatū family with inherited MH. About 2500 members whakapapa back to that Scottish whaler. There’s also another large whānau with branches in Northland, the East Coast and Rotorua with a different MH-causing genetic variant.
Around the world, MH reactions account for about one in 10,000 people. But the medical lead at the national malignant hyperthermia unit, Dr Terasa Bulger, says in the Manawatū area one in 80 patients is treated as if they have the condition due to their family history or having tested positive for MH.
If you need an anaesethetic anywhere in New Zealand you’ll be asked a range of questions including whether any relative has previously had a bad reaction. If there are any concerns, or the patient’s family includes particular family names, patients undergo a blood test for the gene variant. But a negative result, with family history, is not enough for the all-clear, and sometimes a muscle biopsy is needed, with the patient flown to Palmerston North for the procedure. About 30 such biopsies are carried out each year.
Conventionally, volatile gases are used as anaesthetics as well as the muscle relaxant suxamethonium, which is also unsafe for MH patients. Instead, these patients are given the intravenous propofol as anaesthetic. All New Zealand anaesthetists are trained in recognising symptoms of MH and every hospital carries the antidote, dantrolene.
Before 1980 and the advent of dantrolene, the death rate from MH reactions was 80%, but there’s been only one death since 1980.
The genetic variant for the Manawatū family was identified by biochemist and now emeritus professor Kathryn Stowell who also developed the blood test to identify the variant.
This is the first of a three-part series into how genetic data will revolutionise diagnosis and medical treatment. You can read the Listener’s main story here and part III here.
