By Robin Smith, Health Content Scientist at 23andMe
In January of 1790, a small band of mutineers from the HMS Bounty evaded capture by the British Navy and settled Pitcairn Island in the South Pacific.
The direct descendants of this crew (and their captive Tahitian “wives”) now number in the thousands on nearby Norfolk Island, where the colony relocated in 1856. Detailed records on Norfolk have been used to construct an elaborate family tree of 6,500 individuals spanning 12 generations, all originating from just 17 colonists.
Bottlenecked populations such as this one are of great interest to geneticists, as they can be used to test ideas about the heritability of common diseases. Modern-day Norfolk Islanders are particularly susceptible to migraines: debilitating headaches that often occur only on one side of the head and can be accompanied by nausea, sensitivity to light and sound, and other vision problems.
Norfolk Islanders are more than twice as likely to suffer from migraines as Caucasians in Europe and North America (25.5 percent vs. 12 percent) and the condition is clearly inherited within families.
Although migraines have been linked to environmental triggers such as caffeine withdrawal and monosodium glutamate (MSG) consumption, the genetic factors that influence them have only recently begun to emerge. The International Headache Genetics Consortium (IHGC) reported a study in the journal Nature Genetics in which a healthy cohort of 4,580 individuals was compared to 2,326 patients afflicted with the most common form of migraines. The IHGC study identified multiple risk regions encompassing genes that play key roles in the development of neurons and the formation of synapses in the brain.
The study found an association between the marker SNP and susceptibility to migraines. Each copy of a “C” at this position increases the odds of migraine by 20 percent.
Previous research by the same group identified three SNPs associated with migraine susceptibility. These markers are thought to indicate the function of a sensor protein involved in neuropathic pain, as well as a gene that regulates levels of the neurotransmitter glutamate.
A question of cause
The underlying cause of the migraines on Norfolk Island remains elusive. A recent study in the journal Neurogenetics suggested a link with variants near genes that regulate serotonin levels. One of many neurotransmitters, serotonin is a messaging molecule produced by specialized brain cells and influences a wide range of human behavior, including appetite, sleep, memory, and mood.
The finding in Norfolk Islanders is consistent with studies showing serotonin imbalances in people suffering from migraines. Moreover, a class of drugs named triptans mimic serotonin and has proven useful in combating the acute effects of migraines. Further study of the unique population on Norfolk Island will hopefully shed more light on this pathway and help to discover new risk factors for migraines.