The risk following a positive screening test was 0.5% for C9orf72 in ALS and 0.4% for HTT in HD when testing repeat expansions, for which the test had sub-optimal performance (sensitivity = 99% and specificity = 90%), and 12.7% for phenylketonuria and 10.9% for ALS SOD1 when testing pathogenic SNVs (sensitivity = 99.96% and specificity = 99.95%). The gene discussed is C9orf72; the disease is Huntington disease.