Association between polymorphisms in the TRHR gene, fat-free mass, and muscle strength in older women

A previous genome-wide association study suggested that polymorphisms in the thyrotrophin-releasing hormone receptor (TRHR) gene contribute to fat-free mass (FFM) variation. The aim of the present study was to examine the association between polymorphisms in the TRHR gene with FFM and muscle strength in older women. Volunteers (n = 241; age = 66.65 ± 5.5 years) underwent quadriceps strength assessment using isokinetics and fat-free mass by dual-energy X-ray absorptiometry. TRHR polymorphisms and ancestry-informative markers were genotyped through standard procedures. No significant difference was observed for rs7832552. Regarding the rs16892496, ANCOVA revealed that appendicular fat-free mass (AFFM) and relative AFFM were significantly different between groups (p = 0.04 and p = 0.05, respectively). Individuals carrying A/A and A/C genotypes respectively showed, on average, an extra 1 kg and 900 g of AFFM when compared to C/C genotype carriers. Also, the C/C genotype group presented a significantly higher chance to have reduced muscle strength. The observations presented here provide further evidence that the rs16892496 polymorphism in the TRHR gene may play a role in FFM variation. Moreover, the results bring the novel insight that this genetic variant can present a modest contribution to muscle strength in older women.

Genomic ancestry, self-reported "color" and quantitative measures of skin pigmentation in Brazilian admixed siblings

A current concern in genetic epidemiology studies in admixed populations is that population stratification can lead to spurious results. The Brazilian census classifies individuals according to self-reported “color”, but several studies have demonstrated that stratifying according to “color” is not a useful strategy to control for population structure, due to the dissociation between self-reported “color” and genomic ancestry. We report the results of a study in a group of Brazilian siblings in which we measured skin pigmentation using a reflectometer, and estimated genomic ancestry using 21 Ancestry Informative Markers (AIMs). Self-reported “color”, according to the Brazilian census, was also available for each participant. This made it possible to evaluate the relationship between self-reported “color” and skin pigmentation, self-reported “color” and genomic ancestry, and skin pigmentation and genomic ancestry. We observed that, although there were significant differences between the three “color” groups in genomic ancestry and skin pigmentation, there was considerable dispersion within each group and substantial overlap between groups. We also saw that there was no good agreement between the “color” categories reported by each member of the sibling pair: 30 out of 86 sibling pairs reported different “color”, and in some cases, the sibling reporting the darker “color” category had lighter skin pigmentation. Socioeconomic status was significantly associated with self-reported “color” and genomic ancestry in this sample. This and other studies show that subjective classifications based on self-reported “color”, such as the one that is used in the Brazilian census, are inadequate to describe the population structure present in recently admixed populations. Finally, we observed that one of the AIMs included in the panel (rs1426654), which is located in the known pigmentation gene SLC24A5, was strongly associated with skin pigmentation in this sample.

ACTN3 R577X Polymorphism and Neuromuscular Response to Resistance Training

The R577X polymorphism at the ACTN3 gene has been associated with muscle strength, hypertrophy and athletic status. The X allele, which is associated with the absence of ACTN3 protein is supposed to impair performance of high force/velocity muscle contractions. The purpose of the present study was to investigate the association of the R577X polymorphism with the muscle response to resistance training in young men. One hundred forty one men performed two resistance training sessions per week for 11 weeks. Participants were tested for 1RM bench press, knee extensors peak torque, and knee extensors muscle thickness at baseline and after the training period. Genotyping was conducted using de DdeI restriction enzyme. Genotype distribution was 34.4% for RR, 47% for RX and 18.6% for the XX genotype. According to the results, the R577X polymorphism at the ACTN3 gene is not associated with baseline muscle strength or with the muscle strength response to resistance training. However, only carriers of the R allele showed increases in muscle thickness in response to training. Key pointsACTN3 Genotype distribution in the present study was similar to others populations (34.4% for RR, 47% for RX, and 18.6% for the XX).The R577X polymorphism at the ACTN3 gene is not associated with baseline muscle strength or with the muscle strength response to resistance training.It appears that the R allele carriers respond better to muscle thickness gains in response to training.

ACE and ACTN3 genotypes in older women: muscular phenotypes

This study examined the association between ACE I/D and ACTN3 R577X polymorphisms and muscle-related phenotypes and their adaptation to resistance training in older women. Volunteers (n=246;age=66.7 ± 5.5 years) underwent quadriceps strength assessment using isokinetics and fat-free mass by dual energy X-ray absorptiometry. 79 volunteers performed 24 weeks of resistance training and 75 were studied as controls. Genotypes were identified by standard procedures. No associations were observed for muscle strength for either gene, but volunteers carrying the D/D genotype presented higher appendicular fat-free mass compared to the I-allele carriers (6.3 ± 0.1 vs. 6.1 ± 0.1 kg/m (2)). The X-allele carriers presented higher relative fat-free mass when compared to homozygous R/R (16.3 ± 0.1 vs. 15.9 ± 0.1 kg/m (2)). All fat-free mass variables were significantly greater for carriers of both X/X and D/D genotypes. In response to RT, only the I-allele carriers significantly increased fat-free mass and a significant training × genotype interaction was noted. These findings do not support a pivotal role for the studied polymorphisms in determining muscle strength in older women, but suggest a modest role in fat-free mass determination. Of note, the results provide a novel insight that these genetic variations may interact to determine muscle mass in older women.