Table 1. Review of the literature regarding XCI pattern in human extraembryonic tissues.
| Material (origin) | Extraembryonic cell lineage | Locus | Results (*) | Authors' conclusion | Ref. | |
| Placenta (full-term) | Placental membranes homogenate | G6PD | 13 skewed (Xp inactive); 9 random | Preferential paternal inactivation | [13] | |
| Placenta (full-term) | Chorionic villi | G6PD | 9 random; 3 skewed (Xp inactive) | Random inactivation | [12] | |
| Chorionic villi# (suction abortion) | G6PD | 8 skewed in some degree (6 Xp inactive and 2 Xm inactive); 1 random | Random inactivation | [16] | ||
| Placenta (full-term) | Fresh amnion | G6PD | 8 skewed (7 Xp inactive and 1 Xm inactive); 3 random | Preferential paternal inactivation | [14] | |
| Cultured amnion | 22 skewed (16 Xp inactive and 6 Xm inactive); 10 random | |||||
| Fresh chorion | 11 random; 9 skewed (8 Xp inactive and 1 Xm inactive) | |||||
| Cultured chorion | 21 skewed (16 Xp inactive and 5 Xm inactive); 11 random | |||||
| Cultured villi | 16 skewed (15 Xp inactive and 1 Xm inactive); 10 random | |||||
| Placenta (full-term) | Cultured cytotrophoblasts isolated from several cotyledons | G6PD | 7 skewed in some degree (5 Xp inactive and 2 Xm inactive); 5 completely skewed (Xp inactive) | Preferential paternal inactivation | [15] | |
| Chorionic villi (elective abortion) | Fresh and cultured villi | G6PD and HPRT | 4 random | Random inactivation | [17] | |
| Chorionic villi# (diagnostic exam) | Fresh trophoblastic cells | AR | 2 skewed (Xp inactive) | Preferential paternal inactivation | [18] | |
| Placenta (full term) | 2 adjacent fragments isolated from the same cotyledon | AR | 5 skewed in some degree (2 Xp inactive; 2 Xm inactive; 1 either Xp or Xm); 2 completely skewed (1 Xp inactive and 1 either Xp or Xm); 1 random | Random inactivation | [27] | |
| 9 non-adjacent fragments isolated from the same placenta | Heterogeneous pattern depending on the cotyledon | |||||
| Chorionic villi# (elective abortion) | Whole (fresh) branch villi | PGK1 | 5 skewed in some degree (always more Xp inactive); 1 random | Non-random inactivation | [19] | |
| Trophoblasts isolated from anchoring villi | 19 skewed (13 Xp inactive and 6 Xm inactive); 11 random | |||||
| Trophoblasts isolated from branch villi | 17 skewed (14 Xp inactive and 3 Xm inactive); 21 random | |||||
| Chorionic villi# (diagnostic exam) | FMR1 | 2 random | Random inactivation | [33] | ||
| Chorionic villi#,¥ (elective abortion) | Cytotrophoblasts | AR | 37 random; 17 skewed in some degree; 1 completely skewed | Both random and skewed inactivation | [20] | |
| Human embryonic stem cells (H9 line) | Human ES cells at passages 45–48 differentiated in trophoblasts | FMR1 | Non-random | Non-random inactivation | [30] | |
(#) villi from first trimester.
(¥) villi from second trimester.
(*) As scored by the respective authors. Xp, paternal X; Xm, maternal X.