Age-dependent sex ratios of motor neuron disease: French nationwide study and meta-analysis.

OBJECTIVE

To examine the relation of age with male-to-female (M/F) ratios and incidence rates of motor neuron disease (MND) in a French nationwide study and meta-analysis of incidence studies.

METHODS

We used data from the French National Health Insurance databases. Patients with incident MND (2010-2014) were identified based on drug claims (riluzole), hospitalization records, death records, and long-term chronic disease benefits. We estimated age-specific M/F incidence ratios using Poisson regression. Poisson, Gompertz, and multistep models were used to model the relation between age and incidence. We performed a meta-analysis (n = 28 studies) and used meta-regression to examine the relation of age with incidence rates and ratios.

RESULTS

In France, we identified 10,848 patients with incident MND (6,021 men, 4,827 women). Incidence was higher in men than in women in all age groups. M/F ratios were significantly different across age groups and followed a quadratic trend ( < 0.001). Between 20 and 49 years, the average M/F ratio was 2.26 (95% confidence interval [CI] = 1.96-2.62); it was 1.41 (95% CI = 1.35-1.47) between 50 and 84 years, and 1.88 (95% CI = 1.64-2.17) after 85 years. Incidence was lower in women than men at younger ages, but increased more steeply in women than men. Similar patterns were observed in the meta-analysis of incidence studies, especially in 19 higher-quality studies.

CONCLUSION

The relation between age and M/F incidence ratios of MND follows a quadratic U-shaped pattern with an abrupt drop after the fifth decade. The change in M/F ratios before and after menopause suggests that reproductive/hormonal protective factors have a role in women and should prompt further studies to explore this hypothesis.