Body mass index is lower in asymptomatic C9orf72 expansion carriers but not in SOD1 pathogenic variant carriers compared to gene negatives.

Objective : To examine the relationship between body mass index (BMI) and genotype among pre-symptomatic carriers of different pathogenic variants associated with amyotrophic lateral sclerosis. Methods : C9orf72+ carriers, SOD1+ carriers, and pathogenic variant negative controls (Gene-Negatives) were included from 3 largely independent cohorts: ALS Families Project (ALS-Families); Dominantly inherited ALS (DIALS); and Pre-symptomatic Familial ALS ( Pre-fALS ). First reported ( ALS-Families ) or measured ( DIALS and Pre-fALS ) weight and height were used to calculate BMI. Age at weight measurement, self-reported sex (male vs. female), and highest education (high school or below vs. college education vs . graduate school or above) were extracted. The associations between BMI and genotype in each cohort were examined with multivariable linear regression models, adjusted for age, sex, and education. Results : A total of 223 C9orf72+ carriers, 135 SOD1+ carriers, and 191 Gene-Negatives were included, deriving from ALS-Families ( n  = 114, median age 46, 37% male), DIALS ( n  = 221, median age 46, 30% male), and Pre-fALS ( n  = 214, median age 44, 39% male). Adjusting for age, sex, and education, the mean BMI of C9orf72+ carriers was lower than Gene-Negatives by 2.4 units (95% confidence interval [CI] = 0.3-4.6, p  = 0.02) in ALS-Families ; 2.7 units (95% CI = 0.9-4.4, p  = 0.003) in DIALS ; and 1.9 units (95% CI = 0.5-4.2, p  = 0.12) in Pre-fALS . There were no significant differences in BMI between SOD1+ carriers and Gene-Negatives in any of the 3 cohorts. Conclusions : Compared to Gene-Negatives, average BMI is lower in asymptomatic C9orf72+ carriers across 3 cohorts while no significant difference was found between Gene-Negatives and SOD1+ carriers.