Space-time clustering of multiple sclerosis cases around birth

Evidence of early childhood as the susceptibility period in multiple sclerosis: space-time cluster analysis in a Sardinian population

The authors analyzed the natural history of multiple sclerosis (MS) before onset to identify the period of susceptibility and exogenous factors that might play a role in causing the disease. Space-time cluster analysis was performed among northern Sardinians, a genetically stable Italian population that showed an increasing risk of MS between 1965 and 1999. Residence changes from birth to clinical onset were recorded for all MS patients with clinical onset between 1965 and 1999 in the province of Sassari. Closeness in space and time was defined as living in the same municipality and differing in year of birth by 1, 2, or 5 years. Analyses were performed for the period from birth to age 25 years or MS onset and in demographic and clinical subgroups. Clustering was substantial in early childhood. Clustering was most marked in the most recent cases, among women, and among patients with early age at onset, a relapsing-remitting course, and in the eastern subarea. No clustering was found when closeness in time was defined as a fixed number of years before onset, which argues against a fixed latency period. Early childhood seemed to be a period of increased susceptibility to MS. This evidence and the increasing incidence of MS in northern Sardinia are compatible with a change in environmental exposure.

Seasonal fluctuation of multiple sclerosis births in Sardinia

Study results from different geographical areas provide some circumstantial evidence that, when compared with the general population, people who later in life develop multiple sclerosis (MS) have a pattern of birth excess numbers in spring and late summer, which may disclose an association with MS-predisposing environmental agents. To identify the presence of season-related cluster of MS birth in Sardinia we have designed a case-control study in the province of Sassari, Northern Sardinia, insular Italy, an area at very-high and increasing risk for MS. Mean birth incidence rate of people with MS (810 cases) on a three-and six-months basis were compared with that of two control populations: the MS unaffected siblings (1069), sharing genetic material with patients, and a representative number of births (247,612) of the general population of the study area. We found that the birth in months peaking in spring significantly represents one risk factor for future MS development. This seasonal deviation of MS births reveals an intriguing epidemiological overlap with common environmental agents, which may open a new scenario of hypothetical explanations for environmental factors perhaps affecting the CNS at the crucial time of myelination or shaping the newborn immune system.