Table 2.
Trait definition, summary statistics, and genetic parameters for tibial cortical and medullary bone chemical composition traits
| Trait | Description | N | Mean ±SD | h2 ±SE | Genetic correlation with Tibia density |
|---|---|---|---|---|---|
| Tibial cortical bone: TGA | |||||
| Cortical water | Water content (%) | 903 |
10.64± 0.9 |
0.02 ± 0.03 | 0.24 ± 0.58 |
| Cortical organic | Organic (collagen) matter weight (%). | 897 |
24.84± 1.3 |
0.09 ± 0.04 | −0.48±0.26 |
| Cortical carbonate | Calcium carbonate content (CO3, %) which is determined as the weight loss in the 600–800 °C range (the remaining weight at 800 °C is phosphate (PO4%) in the mineral). | 898 | 3.64 ± 0.6 | 0.03 ± 0.03 | −0.06±0.49 |
| Cortical mineral | Minerals weight (%); calculated as the sum of carbonate (%) and phosphate (%). | 898 |
64.49± 1.4 |
0.09 ± 0.03 | 0.37 ± 0.21 |
| Tibial cortical bone: FTIR | |||||
| Cortical PO4/Amide I | Relative amount of mineral to organic matrix (Amide I) in tibia bone which indicates the degree of mineralization in bone. | 893 | 3.5 ± 0.8 | 0.01 ± 0.001 | −0.98±0.59 |
| Cortical MinCO3 870 | The amount of carbonate substituted in the mineral as the ratio of CO3 (870 cm−1) to the main phosphate (900 to 1200 cm−1) band area. This measurement is related to bone mineral maturation. | 897 | 0.07 ± 0.0 | 0.001 ± 0.0 | 0.95 ± 0.8 |
| Cortical MinCO3 1415 | The total amount of carbonate in bone mineral; determined as the ratio of the main carbonate band (1415 cm−1) to the main phosphate (900 to 1200 cm−1) band area ratio. This is an indicator of bone mineral maturation and bone remodeling rate (decreases with bone mineral maturation and bone tissue age [16]. | 899 | 0.25 ± 0.0 | 0.03 ± 0.03 | 0.65 ± 0.92 |
| Cortical CO3/Amide I | Carbonate (CO3, at main peak 1415 cm−1) relative to organic matter (Amide I, at main peak 1640 cm−1); it refers to the degree of bone mineralization process [15]. | 894 | 0.85 ± 0.1 | 0.01 ± 0.001 | −0.98 ±0.66 |
| Cortical CO3 1450/1415 | Ratio of secondary carbonate and organic matter peak (1450 cm−1) to the main carbonate peak (1415 cm−1). Associated with the substitution of carbonate within the bone mineral. | 901 | 0.81 ± 0.1 | 0.03 ± 0.03 | 0.23 ± 0.5 |
| Cortical CO3 870/1415 | Ratio of secondary carbonate and organic matter peak (870 cm−1) to the main carbonate peak (1415 cm−1). This ratio is used to assess the relative amount of secondary carbonate and organic matter compared to the primary carbonate. | 899 | 0.28 ± 0.1 | 0.01 ± 0.00 | −0.99 ±0.0 |
| Cortical crystallinity index | Crystallinity index of the bone determined through the ratio between the peak areas at 1030 cm−1 to 1020 cm−1. It provides information about the degree of crystallinity of the bone’s mineral phase. | 906 | 0.52 ± 0.1 | 0.04 ± 0.03 | 0.30 ± 0.64 |
| Cortical collagen maturity | Mature relative to immature collagen cross-links; mature and immature collagen measured as the FTIR area at main peak 1660 cm−1 and 1690 cm−1, respectively; this measurement is used as an indicator of the collagen maturity. | 893 | 3.78 ± 0.9 | 0.02 ± 0.02 | −0.99 ±0.09 |
| Cortical lipids | Carbonyl group from the lipid; measured as the FTIR area at main peak 1710 cm−1. | 896 | 0.02 ± 0.0 | 0.05 ± 0.03 | −0.01 ±0.38 |
| Cortical sulfates | Sulfate content. If this value is high, it changes the bone properties. | 892 | 0.17 ± 0.0 | 0.05 ± 0.03 | 0.09 ± 0.39 |
| Cortical Amide II/Amide I | Ratio of Amide II relative to organic matter (Amide I) which can suggest alterations in the collagen secondary structure, reflecting bone integrity. | 903 | 0.86 ± 0.1 | 0.06 ± 0.04 | −0.08 ±0.36 |
| Tibial medullary bone: TGA | |||||
| Medullary water | Medullary water weight (%) | 928 | 9.94 ± 1.7 | 0.01 ± 0.02 | 0.31 ± 1.15 |
| Medullary organic | Medullary (collagen) matter weight (%) | 926 | 51.11 ± 9 | 0.19 ± 0.07 | −0.7 ±0.08 |
| Medullary carbonate | Medullary carbonate weight (CO3, %) | 911 | 5.31 ± 6.8 | 0.01 ± 0.01 | −0.27 ±0.48 |
| Medullary mineral | Minerals weight (%); calculated as the sum of carbonate (%) and phosphate (%). | 923 | 38.73 ± 8.4 | 0.18 ± 0.07 | 0.72 ± 0.08 |
| Tibial medullary bone: FTIR | |||||
| Medullary PO4/Amide I | As in cortical | 924 | 0.69 ± 0.3 | 0.07 ± 0.05 | −0.21 ±0.46 |
| Medullary MinCO3 870 | As in cortical | 931 | 0.01 ± 0 | 0.03 ± 0.02 | −0.14 ±0.62 |
| Medullary MinCO3 1415 | As in cortical | 918 | 0.51 ± 0.2 | 0.02 ± 0.02 | 0.87 ± 1.24 |
| Medullary CO3/Amide I | As in cortical | 913 | 0.33 ± 0.1 | 0.01 ± 0.0 | 0.87 ± 1.44 |
| Medullary CO3 1450/1415 | As in cortical | 914 | 0.96 ± 0.1 | 0.03 ± 0.03 | −0.05 ±0.39 |
| Medullary CO3 870/1451 | As in cortical | 921 | 0.03 ± 0 | 0.04 ± 0.05 | −0.21 ±0.49 |
| Medullary crystallinity index | As in cortical | 932 | 0.58 ± 0.4 | 0.002 ± 0.01 | 0.99 ± 0.61 |
| Medullary collagen maturity | As in cortical | 923 | 3.45 ± 0.4 | 0.05 ± 0.06 | 0.28 ± 0.37 |
| Medullary lipids | As in cortical | 924 |
11.45± 25.4 |
0.02 ± 0.02 | −0.27±0.63 |
| Medullary sulfates | Sulfates content | 921 | 0.12 ± 0 | 0.12 ± 0.07 | −0.26 ±0.34 |
| Medullary Amide II/Amide I | As in cortical | 924 | 0.84 ± 0.1 | 0.06 ± 0.06 | 0.22 ± 0.55 |
N, number of records; Mean ±SD, trait phenotypic mean and standard deviation; h2, heritability; SE, standard error. Heritability estimates are presented as h2 ± SE
TGA, thermogravimetric analysis; FTIR, fourier-transform infrared spectroscopy
Tibial density was selected as the reference trait for assessing genetic associations between bone composition and whole-bone mechanical and density traits, as it had the highest heritability among these traits