Motor Neuron Disease

Motor neuron disease (MND) is a rare condition that progressively damages parts of the nervous system.

Motor neuron disease usually presents in the early stages with:

weakness in the ankles or legs
weakened grip with difficulty opening jars
a tendency to drop things
cramps and twitches in the muscles.

In later stages, there will be visible muscle wasting and even slurred speech and difficulty swallowing.

genes and mutations

According to the Australian MND Association, only about 10% of MND cases are “familial”, meaning more than one person in the family suffers from it. Thus, 90% of cases are referred to as sporadic MND, and the cause is unknown.

The role of genetics in MND is intricate, but researchers have found that people with familial MND have the disorder because of a mutation in a gene, which causes the gene to function abnormally. This genetic mutation can be passed on through generations. In some cases, if a parent has a genetic mutation, their child has a 50/50 chance of inheriting MND. People who inherit an MND-related genetic mutation have a high but uncertain chance of developing motor neuron disease, and not all people with this gene will inherit the disease.

a neurologist’s opinion

Can this mutation be detected early and treated? Dr Franclo Henning, a neurologist in Cape Town and the chairman of the Motor Neuron Disease Association of South Africa (MNDASA), says it can be picked up by testing for the mutation that the parent has, but nothing can be done about it, even if detected before it shows signs.

“Even in familial cases of MND, the disease mostly manifests in adulthood,” says Henning. The reason is not quite clear. Henning adds that one of the theories is that the disease only manifests once combined with “normal wear and tear” of advancing age. Another possibility, he says, is that the damage caused by the mutation takes time to accumulate and only shows symptoms later in life.

other culprits

Some researchers have indicated that a virus, which lies latent within the system for a long period, could cause MND. Henning refutes this: “There is absolutely no evidence for the disease being caused by a virus. The cause of sporadic MND is still unknown. Most experts believe it is caused by a combination of genetic predisposition and certain environmental triggers, still unknown.”

He says there is another theory doing the rounds that the cause of sporadic MND is minute variations in the DNA that needs an additional factor, such as an environmental trigger, to cause the disease. This could also be one of the reasons why it’s so difficult to find the cause. Henning adds that another important consideration is that MND is probably not a disease, but a syndrome. “In other words, it is a collection of different diseases that share certain characteristics.”

is sport a trigger?

Recent celebrity sport stars, such as the late Joost van der Westhuizen, who passed away as a result of motor neurone disease have brought sport into the spotlight. Many sports-mad South Africans are now taking notice of a disease first described in 1874.

Should parents be worried?

“There is absolutely no proof that trauma injuries on the sports field can be linked to MND,” says Henning. He adds that repeated head trauma does carry risks. Boxers, for instance, can develop a form of dementia and a condition called chronic traumatic encephalopathy. However, there is a world of difference between a sport like boxing, where the aim is to inflict injury, and rugby, where injury is the unfortunate side effect.

“The sum of evidence from many population-based studies conducted over many years has shown that exercise is not a risk factor for MND,” says Henning.

Some 10 to 20 new cases per million are reported each year, but according to Henning, it is unlikely that taking part in sport alters one’s risk of developing motor neuron disease.

motor neuron disease at a glance

Most people diagnosed with MND are over 40 years old.
Only 10% of people with MND develop it before the age of 45.
The highest incidence occurs between the ages of 50 and 70 years old.
Men are affected twice as often as women. There is an increase in the amount of cases diagnosed worldwide, but this is most likely due to more accurate diagnostic testing. Because people tend to live longer, the incidence of a disease more common in older people will continue to increase.
If a parent has familial MND, children can be tested for the mutation, but this cannot be done in South Africa. DNA samples get sent overseas.