The epidemiology of MND

The epidemiology of MND

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This is blog number 4 in our ‘Symposium Blogathon’ – counting down to the 32nd International Symposium on ALS/MND. Numbers in bold green text correspond to the code in the abstract book. Click on the number to be redirected to the full abstract (the page may take a minute to load).

Epidemiology is the study of the frequency, pattern, causes and risk factors of health-related states and events (not just diseases) in specified populations such as neighbourhoods, countries or globally. Epidemiological information is used to plan and evaluate strategies to prevent illness and as a guide to the management of patients in who disease has already developed.

The causes of MND are still not fully understood. Between 80-90% of people with MND have a sporadic form of the disease – when the disease appears for no apparent reason and with no known familial link. Sporadic MND is thought to be caused by a combination of genetic, environmental and lifestyle influences. Although exposure to these risk factors, which include electric shock, military service, high levels of physical activity, agricultural chemicals and heavy metals, have been extensively studied the evidence gathered offers no clear conclusions. Epidemiological studies may help us to understand the causes and mechanisms of motor neuron degeneration and, in so doing, identify potential drug targets and other therapies.

Blog | 3 August 2018 | Dr Nick Cole
Steps to understanding MND

Currently there is no nationwide register that records clinical information about people with MND, and the true numbers of people living with the disease in the UK is not known. The MND Register of England, Wales and Northern Ireland aims to collect information about every person with MND in the UK. Having accurate, complete information about who has MND is important so that researchers can work out how the disease is changing over time, check if resources are concentrated in areas with lots of people with MND, analyse geographical risk factors at a country level and ensure information about disease progression will be more accurate and applicable to all people with MND.

Every single person with MND can help the global effort to find causes, treatments and ultimately a cure for MND by joining the MND Register.

How epidemiology is helping to shed light on the number of people living with MND

Researchers in Australia have carried out a study to provide incidence and prevalence data for MND in South Australia, to help outline the impact the disease has upon the state. The Global Burden of Disease project recently estimated the MND all-age global prevalence to be 4-5 per 100,000 persons. The aim of this study was to assess if the prevalence and incidence in South Australia, using registry data, was in line with global estimates.

What is prevalence and incidence?

Prevalence is the number of cases of a disease in a specific population at a particular timepoint or over a specified period of time.

Incidence is the rate of new cases of a disease occurring in a specific population at a particular period of time.

The factor connecting prevalence and incidence statistics is the length of time the disease is present for before patients die or are cured.

A total of 256 MND patients were identified between 2017-2019 from the Australian Motor Neurone Disease Registry. Based on the 2016 population of 1,676,653 persons, the estimated prevalence was 6.79 per 100,000 persons. These results indicate that the prevalence and incidence of MND in South Australia are high compared to global estimates (EPI-07).

The incidence of MND in people of Bangladeshi, Indian and Pakistani ethnicity has not previously been reported. In a project funded by the MND Association, researchers in the UK investigated the incidence of MND within these ethnic groups and compared it to that of adults of non-Indian subcontinent ethnicities in England between 1998-2019.

The QResearch database in England identified MND cases in 19 Bangladeshi, 69 Indian and 32 Pakistani adults and 6,317 non-Indian subcontinent ethnicity adults over the study period. Although crude incidence rate – which relates to results for a population as whole, without subdivision or refinement – of MND was lower in Bangladeshi, Indian and Pakistani adults than those of non-Indian subcontinent ethnicity in England, their age-adjusted incidence of MND – a statistical process applied to rates of disease which allows communities with different age structures to be compared – was similar to that of adults of non-Indian subcontinent ethnicity in England in 1998-2019 (EPI-09).

Using epidemiology to better understand the mechanisms of MND

The current lack of treatment for MND is largely attributed to the fact that the cause, or causes, of most individual’s disease is not known. The objectives of a study carried out in Sweden were to create a better understanding of the disease mechanisms by studying how biomarkers, lifestyle and environmental factors are related to the risk or prognosis of MND.

ALSrisc is a case-control study that started in 2015 which follows patients from diagnosis to death, and all newly diagnosed cases from the ALS Center Karolinska in Stockholm, Sweden are recruited.

ALSrisc collects clinical data, questionnaire data and biological samples and patients also undergo additional clinical testing. Information on environmental factors (i.e., housing, employment, military, physical activity), family medical history and dietary habits is collected from both the cases and controls using questionnaires (there are two control groups: a sibling – shared genetic and early-life environmental factors, and a spouse – shared adult-life environmental factors). Cognitive and mental health data are also collected at 6-month intervals from people with MND. Biological samples are collected from all groups, creating a biobank of paired samples, and then annually from people with MND.

Data collection in ALSrisc is ongoing but the data so far shows that average age at diagnosis is 65.9 years and the average delay in diagnosis is 1.4 years. The characteristics of ALSrisc cases are generally comparable to those of all ALS patients diagnosed in Stockholm during the same period according to the MND Quality Registry (EPI-13).

Focus on Kennedy’s disease

Kennedy’s disease (also known as spinal bulbar muscular atrophy or SBMA) is a rare disorder of the motor neurones, caused by a genetic mutation. This genetic mutation causes damage to the nerves that control voluntary muscle movement. This is why it shares some of the same symptoms as MND.

Kennedy’s disease progresses slowly, leading to weakness, wasting of muscles and hormonal changes. Most people with the disease start to show symptoms when they are 30-60 years old, but it can appear in older or younger people. 

There is currently no known cure, but symptoms can be managed to improve quality of life. Most people with the disease live an average life span.

Men are usually affected. Most women who inherit the gene do not develop symptoms, but they can pass it on to their sons or daughters. In rare cases, women may develop symptoms, but these are usually milder than those experienced by men. As little is known about the disease in women, further research is ongoing.

The MND Association supports people with or affected by Kennedy’s disease. 

Kennedy’s disease manifests as a male-specific, adult-onset disorder characterised by progressive neuromuscular symptoms, and has also been associated with a variety of non-neurological conditions including diabetes, fatty liver and metabolic syndrome (a combination of diabetes, high blood pressure and obesity). Kennedy’s disease is estimated to occur in around 1 in 50,000 males, but the frequency of the AR repeat expansion – the genetic variant that causes Kennedy’s – in the general population is unknown.

Researchers from the UK, the Netherlands and the USA investigated the prevalence of the genetic variant underlying Kennedy’s disease and found the frequency of repeat expansion to be higher than expected. This may be due to underdiagnosis of the condition, but highlights the need to test for the defect in neuromuscular clinics and in people with metabolic syndrome features (EPI-17).

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