Which statement accurately describes the distribution of sporadic versus familial ALS?

• A. Sporadic accounts for about 90%; familial about 10%
• B. Sporadic accounts for about 50%; familial about 50%
• C. Sporadic accounts for about 10%; familial about 90%
• D. They do not differ in frequency

Answer: (A)

Most cases of ALS occur without any family history, so they are classified as sporadic, while a smaller portion is due to inherited gene mutations and runs in families. Epidemiology shows sporadic cases make up roughly 90% of ALS, with familial cases around 10%. That pattern is why the statement describing about 90% sporadic and 10% familial is the best description. The other options either imply an equal split, a reversed distribution, or no difference, which doesn’t align with what is observed in ALS populations. This distribution matters because it informs genetic counseling and testing practices: most patients won’t have a family risk, but when there is a positive family history, genetic factors are more likely to be involved.