LAUSR

We read with great interest the editorial by Soysal et al. entitled “Validation of population-based cut-offs for low muscle mass and strength” [1]. The editorial underscores the study by Pal et al. that happens to be the first comprehensive study from India wherein cut-offs to define low muscle strength and low muscle mass have been established and the prevalence of sarcopenia has been estimated based on the indigenous cut-offs. The study has clearly shown that using ‘fixed’ Western cut-offs leads to an overestimation of sarcopenia in India, thereby, necessitating the use of ethnic-/ population-specific cut-offs [2]. The editors have also commented on a recent study by Ates Bulut et al. that was designed to determine the cutoff points of low muscle mass and muscle strength in the Turkish population. The cut-offs were derived according to the European Working Group on Sarcopenia in Older People (EWGSOP) consensus based on a cohort of 208 healthy young volunteers. Low muscle mass was defined as skeletal muscle mass index (SMI) < 8.33 kg/m2 in men and < 5.70 kg/ m2 in women measured using bioelectrical impedance analysis. Thresholds defining low muscle strength was handgrip strength (HS) < 28 kg in men and < 14 kg in women [3]. Surprisingly, the HS cut-offs were very similar to those proposed in the study by Pal et al., being 27.5 kg in men and 18 kg in women [2]. On the contrary, the study by Bahat et al. among the Turkish population found a HS cut-off of 32 kg in men and 22 kg in women. Likewise, the cut-offs defining low muscle mass were also remarkably higher as compared to the study by Ates Bulut et al. (SMI < 9.2 kg/m2 in men and < 7.4 kg/m2 in women) [4]. The marked disparity in the two studies conducted apparently on the same Turkish citizens and the relative similarity in the studies by Ates Bulut et al. and Pal et al. can be explained based on Turkey’s multiethnic make-up. Turkey lies at the crossroads of the Middle East, Europe, and Central Asia and has served as a bridge between the West and East. Turkey has witnessed migrations from different regions throughout history, mostly during the Ottoman Empire that stretched across the Anatolian peninsula (present-day Turkey), the Middle East, southeastern Europe, and southwestern Asia. Large-scale migrations across the entire extent of the Ottoman Empire are reflected in the present-day Turkish population. Analysis of population genetic substructure using high-density single nucleotide polymorphism (SNP) arrays has revealed a marked genetic similarity between the inhabitants of Turkey with those of the Middle East, Europe, South Asia, and Central Asia [5]. India being a part of South Asia also shares a genetic ancestry with Turkey. As muscle strength is genetically determined and is highly transmissible [6], the common genetic makeup between Turkey (at least a subpopulation of Turkey) and India could potentially explain the apparent similarity in the HS cut-offs between the two studies [2, 3]. Similarly, the study by Bahat et al. probably had a preponderance of Turkish men and women sharing an European genetic ancestry, rather than a South Asian one, that could explain the relatively high HS and SMI cut-offs [4]. A reanalysis of the study populations by Ates Bulut et al. and Bahat et al., respectively, may help throw some light on this issue.