Our findings have several implications for clinical genetic testing practice: (1) the offer of the C9orf72 HRE test is indicated for ALS-FTD patients of underrepresented REA in North America; (2) Additional comprehensive genetic testing should be offered for patients of underrepresented REA, either concurrently or as a second step if negative for the HRE; (3) patients with early-onset ALS-FTD should also be considered candidates for comprehensive genetic testing. Here, C9orf72 is linked to amyotrophic lateral sclerosis.