Digit ratios and their asymmetries as risk factors of developmental instability and hospitalization for COVID-19

Abstract

COVID-19 presents with mild symptoms in the majority of patients but in a minority it progresses to acute illness and hospitalization. Here we consider whether markers for prenatal sex hormones and postnatal stressors on developmental instability, i.e. digit ratios and their directional and unsigned asymmetries, are predictive of hospitalization. We focus on six ratios: 2D:3D; 2D:4D; 2D:5D; 3D:4D; 3D:5D; 4D:5D and compare hospitalized patient and control means for right, and left ratios, directional asymmetries (right–left) and unsigned asymmetries [|(right–left)|]. There were 54 patients and 100 controls. We found (i) patients differed in their digit ratios from controls (patients > controls) in all three ratios that included 5D (2D:5D, 3D:5D and 4D:5D) with small to medium effect sizes (d = 0.3 to 0.64), (ii) they did not differ in their directional asymmetries, and (iii) patients had greater |(right–left)| asymmetry than controls for 2D:4D (d = .74) , and all ratios that included 5D; 2D:5D (d = 0.66), 3D:5D (d = .79), 4D:5D (d = 0.47). The Composite Asymmetry of the two largest effects (2D:4D + 3D:5D) gave a patient and control difference with effect size d = 1.04. All patient versus control differences were independent of sex. We conclude that digit ratio patterns differ between patients and controls and this was most evident in ratios that included 5D. Large |(right–left)| asymmetries in the patients are likely to be a marker for postnatal stressors resulting in developmental perturbations and for potential severity of COVID-19.

Right–left digit ratios, a novel form of asymmetry: Patterns of instability in children and relationships to platelet counts and hospitalization in adults with COVID-19

“…2D:5D, 3D:5D, 4D:5D) and also for 2D:4D. The two ratios with the largest effect sizes for these patient-control differences were 2D:4D and 3D:5D and together their composite asymmetry gave a patient-control effect size of d = 1.04 (1).…”

“…The study of Kasielska-Trojan et al (1) was limited by lack of knowledge concerning the properties of unsigned digit ratio asymmetries and by the relatively small sample of patients (1). The latter meant that associations between patient asymmetries and laboratory tests might be unreliable.…”

“…Therefore, in order to inform effective public health measures, it is of importance to be able to identify patients who are at elevated risk of progression to severe illness. Kasielska-Trojan et al (1) have suggested that high digit ratio asymmetries (putative markers of postnatal stress and consequent developmental instability) are linked to a tendency to develop more severe COVID-19. They considered digits two to five (2D, 3D, 4D, 5D), calculated six ratios (2D:3D, 2D:4D, 2D:5D, 3D:4D, 3D:5D, 4D:5D) and focused on links between COVID-19 and the unsigned Right-Left asymmetries of each ratio (|R-L|).…”

Systematical assessment of digit ratio in a female masculinization disease: polycystic ovary syndrome

“…Some studies reported a subtle difference in the finger length pattern of women with PCOS, but a few studies found no difference for 2D:4D between PCOS and controls. Besides 2D:4D, other ratios of digit length were reported to present sexual differences in humans ( 15 , 16 ). However, previous studies related to digit ratio and PCOS were confined to 2D:4D and lacked evidence of other digit ratios in PCOS.…”