I’ve heard that multiple sclerosis is more likely to occur in people raised in the northern areas of the globe. They said on television that they think the same is true for Perthes disease (which is what I have). In fact, they said the lowest rate of Perthes is at the equator. Any idea why that would be?

Research has indeed shown us that Legg-Calvé-Perthes occurs more often in certain geographical areas. For example, children in Northern Europe have the highest rate of occurrence while children around the equator have the lowest incidence. In fact, for every 10 degree increase in latitude, the number of children affected by Perthes doubles.

Researchers have uncovered two possible environmental factors: second hand smoke from cooking stoves and tobacco as well as lower socioeconomic status. Children in families with lower incomes appear to be at greater risk.

Studies of children in England over a period of three decades (30 years) clearly showed a higher incidence among families in the northern part of the country, especially those from areas of socioeconomic deprivation. Over time, as wealth increased in those areas, the incidence of Perthes was reduced by 50 per cent.

Although these variables have been uncovered, the exact way in which these things contribute to Perthes disease remains unknown.