Table 2.
Reviewed studies examining chorionicity with a behavioral genetic design
| Reference | N (twin pairs)a | Location | Placentation determination | Age | Comparison | Analysis | Outcome | Effect | Other notes |
|---|---|---|---|---|---|---|---|---|---|
| Birth weight (BWT), early growth | |||||||||
| Buzzard et al. (1983) | 52 MZMC 40 MZDC 72 DZDC |
Canada | Placental pathology | 20–41 years | MC versus DC and MZ versus DZ | Intra-pair differences | BWT | MC = DC; MZ = DZ | Trends for intra-pair differences in chorionicity and chorionicity by sex interaction |
| Vlietinck et al. (1989) | 762 MZ 1093 DZ |
Belgium | Examination of placenta | Birth | MZMC versus MZDC versus DZ | Extended ACE model with chorionicity included | BWT | rMC < rDC (MC also less variable than DC) | EFPTS |
| Gielen et al. (2008) | 4232 twin pairs | Belgium | Examination of placenta | Birth | MZ versus DZ, chorionicity a covariate | ACE models, chorionicity a covariate | BWT | Removing chorionicity resulted in a decrease of genetic variance and heritability | EFPTS |
| Touwslager et al. (2010) | 522 individuals | Belgium | Examination of placenta | 0–2 years | MZMC versus MZDC versus DZ | Intra-pair growth correlations | Growth during infancy | rMZMC = rMZDC at 0-1, 0-6, or 6-12 months; rMZMC > rMZDC at 12-24 months; | EFPTS; MZMC grew more slowly than MZDC |
| Misc. screening/vaccination | |||||||||
| Wojdemann et al. (2006) | 31 MC 150 DC |
Denmark | Ultrasound | Birth | MC versus DC | ICCs | Nuchal translucency | rMC = rDC | |
| Gupta et al. (2008) | 117 DC 16 MC |
India | Examination of placenta | Newborns | MC versus DC and MZ versus DZ | Intra-pair agreement | BCG vaccine reaction | rMC = rDC; rMZ = rDZ | |
| Handedness | |||||||||
| Carlier et al. (1996) | 20 MZMC 24 MZDC 24 DZ |
France | Examination of placenta | 8–12 years | MZMC versus MZDC versus DZ | Comparison of difference between groups on the average absolute twin difference; if chorion effect not significant, all MZs pooled for MZ/DZ comparison | Manual performance, direction, laterality (handedness) | No chorionicity effects | rMZ = rDZ in classic twin design (chorionicity not controlled) |
| Melnick and Myrianthopoulos (1979) | 117 MZMC 56 MZDC |
USA | Sex, nine blood groups, and gross and microscopic examination of placenta | Birth through 7 years | MZMC versus MZDC | Comparing concordance | Finger ridge count and right-left asymmetry of ridge count and congenital anomaly (e.g., differentiation of body parts, tissue differentiation or dysplasias) | rMZDC < rMZMC for total ridge count. No chorionicity effects for congenital anomalies, other assessments of dermatoglyphics | NCPP twin population |
| Anthropomorphic measures | |||||||||
| Corey et al. (1976) | 30 MZMC 22 MZDC |
USA | Examination of fetal membranes | Newborns | MZMC versus MZDC | General linear model for twin data, applied to MC and DC twins | Cholesterol from cord blood | Chorion type had a sig effect on within-pair not among-pair variation. rMC > rDC | Female MZ > male MZ for cord blood cholesterol |
| Hur and Shin (2008) | 81 MCMZ 47 DCMZ 457 DZ |
S. Korea | Examination of placenta | 2–9 years (mean = 4 years) | MZMC versus MZDC versus DZ | ACE models including chorion effects | Height, weight, BMI | A + C sig. chorion effects for height sig but only 4 %, not sig for weight/BMI | |
| Blekher et al. (1998) | 17 MZMC 16 MZDC |
USA | Examination of placentas | 9–18 years (mean 13.2 years) | MZMC versus DC | ICCs | Saccadic eye movements: accuracy, slope, velocity at 15 degree saccade | rMZMC > rMZDC for reaction times; not phasic component of saccadic command. | Follows up a traditional MZ/DZ study showing sig. genetic influence |
| Souren et al. (2007) | 240 MZ 138 DZ |
Belgium | Examination of placenta | Adults | MZMC versus MZDC | ICCs | Body mass, BMI, fat mass, waist-to-hip ratio, sum of four skinfold thickness, lean body mass, fasting glucose, fasting insulin, insulin resistance and beta cell function, and insulin-like growth factor binding protein-1 levels, total, LDL, HDL, total:HDL ratio for cholesterol, triacylglycerol, NEFA and leptin levels | rMZMC = rMZDC | EFPTS; regular twin study run subsequently |
| van den Borst et al. (2012) | 165 MZ 71 DZ 102 single twins |
Belgium | Examination of placenta | Adults | MZMC versus MZDC | ICCs | Lung measures: forced expiratory volume in 1 s and forced vital capacity | rMZMC = rMZDC | EFPTS; regular twin study run subsequently |
| Fagard et al. (2003) | 125 DZ 97 MZDC 128 MZMC |
Belgium | Examination of placenta | 18–34 years | MZMC versus MZDC versus DZ | Intra-pair correlations; ACE models fit to MZ/DZ; MZDC/DZ; MZMC/DZ | Conventional and ambulatory blood pressure | rMZMC = rMZDC Heritability estimates similar when MZ/DZ or MZMC/MZDC | EFPTS |
| Loos et al. (2001a) | 280 MZMC 212 MZDC 311 DZ |
Belgium | Examination of placenta | 18–34 years | MZMC versus MZDC versus DZ | Intra-pair concordance | Abdominal obesity | Contribution of zygosity and chorionicity low (< 1.7 %) for adult weight. rDC > rMC for BWT only | EFPTS |
| Loos et al. (2001b) | 67 MC 56 DC |
Belgium | Examination of placenta | M = 25 years | MZMC versus MZDC versus DZ | ICCs | Fasting fibrinogen |
rMZMC < rMZDC Suggested chorionicity effect would change heritability |
Article type = “Correspondence” about EFPTS rMZ > rDZ |
| Cognitive and brain measures | |||||||||
| Mukherjee et al. (2009) | 22 MZMC 17 MZDC 49 DZDC |
USA | Placental pathology, or ultrasound if pathology not performed or unavailable | Prenatal and birth | MZMC versus MZDC versus DZ | Comparing concordance | Head circumference and weight at 22 weeks, 32 weeks, birth, and intracranial volume | rMZMC = rMZDC head circumference and weight; Sig. group difference on ICV (DZ > MZMC and MZDC) | |
| Welch et al. (1978) | 20 MZMC 12 MZDC |
USA | Gross and microscopic placental examination | 18 months | MZMC versus MZDC | Differences in within-pair mean squares | BWT, Bayley mental development scores | rDC > rMC for BWT; not significant (in opposite direction) for Bayley | Positive correlation of BWT and Bayley |
| Melnick et al. (1978) | 86 MZ 173 DZ |
USA | Sex, nine blood groups, and gross and microscopic examination of placenta | 7 years | MZMC versus MZDC and MZDC versus DZ | Heritability estimates | IQ | heterogeneity between MZMC/DZ total variances, but not MZDC/DZ. Estimated genetic variance comparing MZMC/DZ not sig diff from 0, but MZDC/DZ was. | NCPP twin population, also split by race |
| Sokol et al. (1995) | 23 MZMC 21 MZDC |
USA | Gross and microscopic examination of placentas | ~6 years | MZMC versus MZDC | Intra-pair differences | McCarthy Scales of Children’ s Abilities and Personality Inventory for Children | rMZMC > rMZDC for 3/4 Personality Inventory for Children factor scales, 8/12 clinical scales, and 2/4 validity/screening scales. No differences on 6 McCarthy scales. | |
| Antoniou et al. (2010) | 663 twin pairs | Belgium | Examination of placenta | 7–15 years, M = 10.4 years | MZ versus DZ on placentation | Bivariate ACE models | BWT-IQ and cord knots-IQ associations | No chorionicity effect | |
| Spitz et al. (1996) | 20 MZMC 24 MZDC 24 DZ |
France | Ultrasound and macroscopic examination at delivery | 8–12 years | MZMC versus MZDC | Intra-class correlations | Anthropometric measures at birth and assessment; Cognitive battery (Vocabulary, block design from WISC-R, K-ABC, perception and mental rotation | rMC < rDC for BWT, child weight, height, BMI. rMC > rDC block design. No chorion effect for vocabulary, K-ABC, perception, or mental rotation | |
| Jacobs et al. (2001) | 161 MZMC 82 MZDC 188 DZ |
Belgium | Examination of placenta | 9–11 years | MZMC versus MZDC versus DZ | ACE models including chorion effects | WISC-R | rMZMC > rMZDC on arithmetic (chorionicity = 14 % of total variance) and vocabulary (chorionicity = 10 %) | EFPTS; High heritability for almost all subscales and IQ scores. |
| Gutknecht et al. (1999) | 20 MZMC 23 MZDC |
France | Examination of placenta | 10–16 years | MZMC versus MZDC | Comparison of average within-pair difference between groups | Weight, height, BMI; WISC-III; figurative reasoning; schools’ standardized exams; Personality and behavioral measures | rMC > rDC weight, BMI; 1/6 WISC-III measures; figurative reasoning, 1/5 personality/behavioral variables (most null) | Lack of power; but found consistent direction of effects in even null findings |
| Rose et al. (1981) | 17 MZMC 15 MZDC 28 DZ |
Canada | Examination of placenta | Adults | MZMC versus MZDC versus DZ | Mean differences, ICCs, heritability estimates (from several contrasts) | WAIS vocabulary and block designs | rMZMC > rMZDC (~ 2x) for block design only; vocabulary: rMZMC = rMZDC > rDZ | |
| Melnick et al. (1980) | 94 MZ 187 DZ |
USA | Gross and microscopic examination of placenta | 4 months and 1 year | MZ versus DZ, checked chorion effects | Within-pair mean square estimates of genetic variance | Anterior fontanelle development | No chorionicity effects at 4 months or 1 year | NCPP twin population, also split by race |
| Other behavioral measures | |||||||||
| Chen et al. (1990) | 44 MZ 18 DZ |
China | Examination of placenta | 6 months | MZ versus DZ and MZMC versus MZDC | Intra-pair correlations | Temperament | rMZMC = rMZDC | Found genetic influences |
| Hur (2007) | 56 MZMC 34 DCMZ 316 DZ |
S. Korea | Examination of placenta | 2–9 years (M = 4 years) | MZMC versus MZDC versus DZ | ACE models including chorion effects | Prosocial behaviors | No chorionicity or shared environment effects. | Twin study estimates good |
| Riese et al. (1999) | 48 MZMC 29 MZDC |
USA | Examination of placenta | Neonates before released from hospital | MZMC versus MZDC | ICCs | Temperament | rMZMC = rMZDC | |
| Wichers et al. (2002) | 202 MZMC 125 MZDC 425 DZ |
Belgium | Examination of placenta | 6–17 years | MZMC versus MZDC versus DZ | ICCs, ACE model | CBCL total problems score | rMZDC = rMZMC > rDZ. Chorionicity effect was 0 in the full ACE model | EFPTS |
Described effects are not necessarily comprehensive. Findings were interpreted by comparing MC and DC similarity (e.g., ICCs)—with MC and DC similarity denoted by r (e.g., the within-twin pair correlation)
a N number of twin pairs unless otherwise noted, MZMC monozygotic monochorionic twins, MZDC monozygotic dichorionic twins, DZDC Dizygotic dichorionic twins, BWT birth weight, MC monochorionic, DC dichorionic, MZ monozygotic, DZ dizygotic, EFPTS East Flanders Prospective Twin Survey, ICC intra-class correlation, BCG Bacille Calmette-Guerin vaccine, NCPP NINCDS Collaborative Perinatal Project, BMI body mass index, LDL low density lipoprotein, HDL high density lipoprotein, NEFA non-esterified fatty acids, ICV intracranial volume, BWT birth weight, WISC Wechsler Intelligence Scale for Children, K-ABC Kaufmann Assessment Battery for Children, WAIS Wechsler Adult Intelligence Scale, CBCL Child Behavior Checklist