Epidemiology and Causes of MS

MS is the most common debilitating illness affecting young adults.

Epidemiology

Incidence: The estimated European mean annual MS incidence rate is 4.3 cases per 100 000. The total estimated prevalence rate of MS for the past three decades is 83 per 100 000 with higher rates in northern countries.

Sex: The male to female ratio is 1:2.

Age: The typical age range of presentation is 20-50 years. Occurrence of MS is very rare under 15 or over 60 years.

Geography: There is a marked geographical and race distribution of MS, with the condition occurring twice as commonly in Caucasians than in any other race.

The incidence is highest in Canada and Scotland.

Overall MS is five times more prevalent in temperate climates than in the tropics, but this increased risk is only associated with childhood years spent in temperate climates [4].

The trigger for the autoimmune process in MS is not clear but is certainly multifactorial with combined genetic, environmental and/or infectious triggers:

Genetic

Genetically, there is a well-established association of the incidence of MS with certain MHC-II alleles.

There is a familial rate of 20% with up to 30% concordance in monozygotic twins but only 5% in dizygotic twins; strongly favouring the existence of a secondary environmental trigger [5].

Environmental

Geographically, the incidence of MS rises with increasing distance from the equator suggesting the lack of sunlight and possibly Vitamin D as potential triggers.

Recently, mechanisms linking the major genetic and environmental risk factors have been identified.

Infectious

Various infectious triggers have also been implicated including human herpes virus 6, Epstein–Barr virus (EBV)and chlamydia

Learning bite

The aetiology of MS includes a complex interaction of environmental factors in genetically susceptible individuals. It occurs most commonly in middle-aged people, females and people who have spent their pre-adult life in northern latitudes.