The sex ratio in amyotrophic lateral sclerosis: A population based study

Abstract

Replicable risk factors for ALS include increasing age, family history and being male. The male: female ratio has been reported as being between 1 and 3. We tested the hypothesis that the sex ratio changes with age in a population register covering the south-east of England. The sex ratio before and after the age of 51 years was compared using a Z-test for proportions. Kendall's tau was used to assess the relationship between age group and sex ratio using incidence and prevalence data. Publicly available data from Italian and Irish population registers were compared with results. There was a significant difference in the proportion of females with ALS between those in the younger group (30.11%) and those in the older group (43.66%) (p = 0.013). The adjusted male: female ratio dropped from 2.5 in the younger group to 1.4 in the older group using prevalence data (Kendall's tau = -0.73, p = 0.039). Similar ratios were found in the Italian but not the Irish registry. We concluded that sex ratios in ALS may change with age. Over-representation of younger patients in clinic registers may explain the variation in sex ratios between studies. Menopause may also play a role.

Figure 1

Relationship between age group and sex ratio (incidence). This figure shows a plot of the age- and sex-adjusted sex ratio by age group. To the right of the vertical line are older age groups (operationally defined in this context as being post menopausal). The male: female ratio is clearly lower in the younger groups.

Figure 2

Relationship between age group and sex ratio (prevalence). This figure shows a plot of the age- and sex-adjusted sex ratio by age group. To the right of the vertical line are the older age groups (operationally defined as post menopausal as with figure 1). The male: female ratio is clearly lower in the older groups.