Do men and women get sick with equal frequency?

Men and women are affected by ALS in almost equal numbers. Men are slightly more likely to be affected. The gender ratio is 1.5 to 1. This ratio means that for every 15 men with ALS, there are about ten women with the disease. It is notable, however, that specific forms of ALS are very strongly associated with men (e.g., flail arm syndrome).

The cause of the marked gender difference is unknown. One theory under discussion is the influence of genes on the sex chromosomes (X or Y chromosome), which determine the risk of ALS or its clinical presentation. This hypothesis is supported by other neurological disorders that share similarities with ALS and are caused by mutations in a sex-linked gene. For example, spinobulbar muscular atrophy (SBMA; Kennedy’s disease) occurs only in men. SBMA leads to muscle wasting (myopathy) and paralysis (paresis) of the tongue and limb muscles—as in ALS. Unlike ALS, however, the paralysis progresses much more slowly. The cause of SBMA lies in a genetic mutation in the androgen receptor gene on a sex chromosome (the X chromosome). SBMA demonstrates that motor neuron diseases can be caused or influenced in a sex-dependent manner (related to changes on sex chromosomes or through hormonal processes).