Author(s): VENCKUNAS, T., CHAILLOU, T., DEGENS, H., SUBOCIUS, A., MINDERIS, P., VANCKAVICIENE, A., WESTERBLAD, H., KAMANDULIS, S., Institution: LITHUANIAN SPORTS UNIVERSITY, Country: LITHUANIA, Abstract-ID: 165

INTRODUCTION:
The common R577X polymorphism within ACTN3 gene renders ~20% of the global human population α-actinin-3 deficient. Because of its effects on skeletal muscle properties such as muscle mass and fiber composition, this genetic variation may also influence whole-body metabolism and thereby modify health and well-being. The objective of the current study was to compare body composition and metabolic health markers between overweight α-actinin-3-deficient (XX) and α-actinin-3-expressing (RR) individuals.
METHODS:
Untrained overweight participants (Men: RR n=20, XX n=20; Women: RR n=21, XX n=19; 43 ± 7 years; BMI 29 ± 3 kg/m2) underwent assessments of segmental body composition and bone mineral content (DXA), m. vastus lateralis thickness (ultrasound), resting metabolism, C-reactive protein, blood lipid profile, glucose tolerance and insulin sensitivity. Data were analyzed using two-way repeated or factorial ANOVA.
RESULTS:
Anthropometrical and body composition features, including body mass, fat %, visceral adipose tissue mass, bone mineral content and vastus lateralis thickness, did not differ between the genotype groups in either women or men. However, individuals with the XX genotype had lower fat-free mass compared with RR individuals, irrespective of sex (genotype effect: p=0.035). There were no differences between the genotype groups in measured resting metabolic rate and fat oxidation rate, blood lipid profile, C-reactive protein level or glucose tolerance. However, women of the XX genotype had a smaller insulin response to the oral glucose tolerance test compared to RR women (genotype effect: p=0.042), while there was no difference in insulin response between RR and XX men.
CONCLUSION:
In conclusion, our results show no major effect of ACTN3 R577X polymorphism on metabolic health and body composition in untrained overweight but otherwise healthy men and women. Nevertheless, a smaller total and lean body mass together with less insulin required to handle a constant glucose load in XX than in RR women is intriguing and calls for further investigation of ACTN3 effects on carbohydrate metabolism.