Monozygotic twins discordant for phacomatosis pigmentovascularis: evidence for the concept of twin spotting.

The term phacomatosis pigmentovascularis (PPV) refers to the occurrence of vascular nevi with melanocytic or epidermal nevi. We report on monozygotic twins (MZTs) discordant for phacomatosis cesioflammea (PPV type II) providing evidence for the mechanism of twin spotting in the development of PPV. The affected twin had a nevus flammeus on the right arm and the right maxilla, and a pigmented area on the trunk in keeping with a persistent, aberrant Mongolian spot. The affected twin had bilateral ocular melanocytosis with abnormal scleral pigmentation, iris mamillations, increased pigmentation of the trabecular meshwork, and increased fundal pigmentation and secondary glaucoma. DNA testing confirmed monozygosity. This case of MZTs discordant for PPV supports the hypothesis that PPV results from mosaicism due to a post-zygotic mutational event and the concept of twin spotting.

Longitudinal study of interpersonal dependency in female twins

Interpersonal dependence is thought to be important in a number of physical and psychological disorders. There are several developmental theories that suggest environmental influences in childhood are important.

Prevalence and risk of Down syndrome in monozygotic and dizygotic multiple pregnancies in Europe: implications for prenatal screening

OBJECTIVE: To determine risk of Down syndrome (DS) in multiple relative to singleton pregnancies, and compare prenatal diagnosis rates and pregnancy outcome.

DESIGN: Population-based prevalence study based on EUROCAT congenital anomaly registries.

SETTING: Eight European countries.

POPULATION: 14.8 million births 1990-2009; 2.89% multiple births.

METHODS: DS cases included livebirths, fetal deaths from 20 weeks, and terminations of pregnancy for fetal anomaly (TOPFA). Zygosity is inferred from like/unlike sex for birth denominators, and from concordance for DS cases.

MAIN OUTCOME MEASURES: Relative risk (RR) of DS per fetus/baby from multiple versus singleton pregnancies and per pregnancy in monozygotic/dizygotic versus singleton pregnancies. Proportion of prenatally diagnosed and pregnancy outcome.

STATISTICAL ANALYSIS: Poisson and logistic regression stratified for maternal age, country and time.

RESULTS: Overall, the adjusted (adj) RR of DS for fetus/babies from multiple versus singleton pregnancies was 0.58 (95% CI 0.53-0.62), similar for all maternal ages except for mothers over 44, for whom it was considerably lower. In 8.7% of twin pairs affected by DS, both co-twins were diagnosed with the condition. The adjRR of DS for monozygotic versus singleton pregnancies was 0.34 (95% CI 0.25-0.44) and for dizygotic versus singleton pregnancies 1.34 (95% CI 1.23-1.46). DS fetuses from multiple births were less likely to be prenatally diagnosed than singletons (adjOR 0.62 [95% CI 0.50-0.78]) and following diagnosis less likely to be TOPFA (adjOR 0.40 [95% CI 0.27-0.59]).

CONCLUSIONS: The risk of DS per fetus/baby is lower in multiple than singleton pregnancies. These estimates can be used for genetic counselling and prenatal screening.

Gene-environment interactions and aging visual function: a classical twin study.

OBJECTIVE:
To elucidate the contribution of environmental versus genetic factors to the significant losses in visual function associated with normal aging.
DESIGN:
A classical twin study.
PARTICIPANTS:
Forty-two twin pairs (21 monozygotic and 21 dizygotic; age 57-75 years) with normal visual acuity recruited through the Australian Twin Registry.
METHODS:
Cone function was evaluated by establishing absolute cone contrast thresholds to flicker (4 and 14 Hz) and isoluminant red and blue colors under steady state adaptation. Adaptation dynamics were determined for both cones and rods. Bootstrap resampling was used to return robust intrapair correlations for each parameter.
MAIN OUTCOME MEASURES:
Psychophysical thresholds and adaptational time constants.
RESULTS:
The intrapair correlations for all color and flicker thresholds, as well as cone absolute threshold, were significantly higher in monozygotic compared with dizygotic twin pairs (P<0.05). Rod absolute thresholds (P = 0.28) and rod and cone recovery rate (P = 0.83; P = 0.79, respectively) did not show significant differences between monozygotic and dizygotic twins in their intrapair correlations, indicating that steady-state cone thresholds and flicker thresholds have a marked genetic contribution, in contrast with rod thresholds and adaptive processes, which are influenced more by environmental factors over a lifetime.
CONCLUSIONS:
Genes and the environment contribute differently to important neuronal processes in the retina and the role they may play in the decline in visual function as we age. Consequently, retinal structures involved in rod thresholds and adaptive processes may be responsive to appropriate environmental manipulation. Because the functions tested are commonly impaired in the early stages of age-related macular degeneration, which is known to have a multifactorial etiology, this study supports the view that pathogenic pathways early in the disease may be altered by appropriate environmental intervention.

Discordant quantitative detection of putative biomarkers in nodal micrometastases of colorectal cancer: biological and clinical implications

Aims: Nodal expression of the carcinoembryonic antigen ( CEA), cytokeratin 20 ( CK20), and guanylyl cyclase C ( GCC) genes was measured in tandem in patients with colorectal cancer ( CRC) to assess whether there would be sufficient agreement between these markers in their ability to detect micrometastasis to qualify one of them as a universal marker, and whether frozen and paraffin wax embedded tissues would yield similar results.

Emotions and Power: Reconciling Conceptual Twins

While the existence of an ‘emotional turn’ within the social sciences is now widely acknowledged, some areas have garnered less specific attention than others. Perhaps the most significant absence within this literature is an explicit exploration of the relationship between emotions and relations of power and domination. This article will attempt such an endeavour. In doing so, I will draw on some key work from within the sociology of emotions, such as Barbalet, Collins, Kemper and Turner, and from the power literature within social theory more generally, including Dahl, Elias, Foucault, Giddens, Gramsci and Lukes. The main thrust of the argument is that power and emotion are conceptual twins in need of a serious theoretical reunion, and that emotions have played a largely unacknowledged, ‘under-labouring’ role within most theories of power. The need for a more unified approach to these two concepts is highlighted.

Heritability of peripheral refraction in Chinese children and adolescents: the Guangzhou Twin Eye study.

PURPOSE:

To estimate the heritability of peripheral refraction in Chinese children and adolescents.

METHODS:

The authors examined 72 monozygotic (MZ) twins and 48 dizygotic (DZ) twins aged 8 to 20 years from a population-based twin registry. Temporal and nasal peripheral refraction, each 40° from the visual axis, and axial refraction were measured using an autorefractor. Relative peripheral refractive error (RPRE) was defined as the peripheral refraction minus the axial refraction. Heritability was assessed by structural equation modeling after adjustment for age and sex.

RESULTS:

The mean and SD of temporal refraction (T(40)), nasal refraction (N(40)), RPRE-T(40), RPRE-N(40), and T(40)-N(40) asymmetry were -0.27 ± 2.0 D, 0.36 ± 2.19 D, 1.18 ± 1.39 D, 1.80 ± 1.69 D, and -0.62 ± 1.58 D, respectively. The intraclass correlations for T(40) refraction, N(40) refraction, RPRE-T(40), RPRE-N(40), and T(40)-N(40) asymmetry were 0.87, 0.83, 0.65, 0.74, and 0.58 for MZ pairs and 0.49, 0.42, 0.30, 0.41, and 0.32 for DZ pairs, respectively. A model with additive genetic and unique environmental effects was the most parsimonious, with heritability values estimated as 0.84, 0.76, 0.63, 0.70, and 0.55, respectively, for the peripheral refractive parameters.

CONCLUSIONS:

Additive genetic effects appear to explain most of the variance in peripheral refraction and relative peripheral refraction when adjusting for the effects of axial refraction.

Contribution of genetic and environmental effects on lens thickness: the Guangzhou Twin Eye study.

PURPOSE:

This study investigated the heritability of lens thickness (LT) and relative lens thickness (LT/axial length, rLT) measured by Lenstar among Chinese children and adolescents in the Guangzhou Twin Eye study.

METHODS:

Twins aged 8 to 22 years were enrolled from the Guangzhou Twin Registry. A series of LT and axial length (AL) measurements using the Lenstar were taken for each twin. Zygosity was confirmed by genotyping in all same-sex twin pairs. Heritability was assessed by structural variance component genetic modeling, after adjustment for age and sex with the Mx program.

RESULTS:

Seven hundred sixty-eight twin pairs (482 monozygotic [MZ] and 286 dizygotic [DZ] twins) were available for data analysis. The mean (standard deviation) LT and rLT were 3.45 (0.18) mm and 0.142 (0.01), respectively. The intraclass correlation coefficients (ICCs) for LT were 0.90 for the MZ and 0.39 for the DZ twins; and those for rLT were 0.90 for the MZ and 0.40 for the DZ twins, respectively. The best-fitting model yielded 89.5% (95% CI: 87.8%-91.0%) of additive genetic effects and 10.5% (95% CI: 9.0%-12.2%) of unique environmental effects for LT, and 89.3% (95% CI: 89.2%-89.3%) of additive genetic effects and 10.7% (95% CI: 10.7%-11.4%) of unique environmental effects for rLT.

CONCLUSIONS:

This study confirms that the LT in young healthy subjects may be mainly affected by additive genetic factors. High heritability remains even when the data are corrected for the influence of AL with the use of rLT.

Stress and coping in parents of newly born twins

Objective: Research indicates that parents of twins have poorer psychosocial outcomes than parents of singletons. Parents who have conceived using assisted reproductive technology (ART) have been found to be at higher risk of negative psychosocial outcomes compared to parents who have conceived spontaneously. The current study aimed to model the factors associated with parenting stress of newly-born twins, using the Transactional Model of Stress.

Methods: Data were collected using a cross-sectional survey design with participants identified from delivery records across Northern Ireland. Mothers and fathers (n = 104) of twins aged between 1 and 12 months old returned a questionnaire pack containing the Parenting Stress Index, Impact on the Family Scale-Financial Burden, Coping Orientation to Problems Experienced – Brief Version, Multidimensional Scale of Perceived Social Support, General Health Questionnaire and a demographic questionnaire.

Results: There were no differences on psychological outcomes between parents who had conceived via ART and those who conceived spontaneously. Regression analyses found that social interaction and support is an important variable in terms of the psychological outcomes experienced by parents of twins.

Conclusion: Parents of newly-born twins regardless of the mode of conception should be considered an at risk group for parental distress. Support groups such as the Twins and Multiple Births Association could be important in providing that crucial social interaction and support that seems to be important in the emotional well-being of parents of twins.

Family-based investigation of the C677T polymorphism of the methylenetetrahydrofolate reductase gene in ischaemic heart disease

Background: Elevated homocysteine is associated with ischaemic heart disease (IHD). The C677T polymorphism in the methylenetetrahydrofolate reductase (MTHFR) gene results in reduced MTHFR enzyme activity and reduced methylation of homocysteine to methionine resulting in mild hyperhomocysteinaemia. Case-control association studies of the role of the C677T MTHFR polymorphism in IHD have produced conflicting results. We therefore used newly described family-based association tests to investigate the role of this polymorphism in IHD, in a well-defined population. Methods: A total of 352 individuals from 129 families (discordant sibships and parent-child trios) were recruited. Linkage disequilibrium between the polymorphism and IHD was tested for using the combined transmission disequilibrium test (TDT)/sib-TDT and pedigree disequilibrium test (PDT). Homocysteine levels were measured. Results: Both the TDT/sib-TDT and PDT analyses found a significantly reduced transmission of the T allele to affected individuals (P=0.016 and P=0.021). There was no significant difference in homocysteine levels between affected and unaffected siblings. TT homozygotes had mean homocysteine levels significantly higher than those of TC heterozygotes (P

Lack of MEF2A Δ7aa mutation in Irish families with early onset ischaemic heart disease, a family based study

Background: Ischaemic heart disease (IHD) is a complex disease due to the combination of environmental and genetic factors. Mutations in the MEF2A gene have recently been reported in patients with IHD. In particular, a 21 base pair deletion (Δ7aa) in the MEF2A gene was identified in a family with an autosomal dominant pattern of inheritance of IHD. We investigated this region of the MEF2A gene using an Irish family-based study, where affected individuals had early-onset IHD. Methods: A total of 1494 individuals from 580 families were included (800 discordant sib-pairs and 64 parent-child trios). The Δ7aa region of the MEF2A gene was investigated based on amplicon size. Results: The Δ7aa mutation was not detected in any individual. Variation in the number of CAG (glutamate) and CCG (proline) residues was detected in a nearby region. However, this was not found to be associated with IHD. Conclusion: The Δ7aa mutation was not detected in any individual within the study population and is unlikely to play a significant role in the development of IHD in Ireland. Using family-based tests of association the number of tri-nucleotide repeats in a nearby region of the MEF2A gene was not associated with IHD in our study group. © 2006 Horan et al; licensee BioMed Central Ltd.