Monozygotic

Schizophrenia is not a neurodegenerative disease but there is some general neuropathology. There is also evidence for a genetic influence. In monozygotic twins with... 

MS probably has a genetic component there is a 5% risk for family members of MS patients. Monozygotic twins, who share the same genetic material, are at highest risk, with a 25% to 30% concordance rate.4 However, a straightforward inheritance pattern cannot fully explain the etiology of MS, because only a small proportion of patients have a known family member with MS.4... 

Results of family and twin studies suggest a genetic basis for bipolar disorder.4 The lifetime risk of bipolar disorder in relatives of a bipolar patient is 40% to 70% for a monozygotic twin and 5% to 10% for another first-degree relative. 

Studies conducted in twins show a threefold increased risk of psoriasis in monozygotic twins versus fraternal twins.7 In addition, based on a study in 3,095 families with psoriasis, the calculated lifetime risk of developing psoriasis if no parent, one parent, or both parents have psoriasis was found to be 0.04, 0.28, and 0.65, respectively. If there was already one affected child in the family, the risks were increased to 0.24, 0.51, and 0.83, respectively.7,9 As many as 71% of patients with psoriasis during childhood have some positive family history.1 Similarly, psoriatic arthritis is heritable, with a prevalence 19 times higher in first-degree relatives of patients with psoriatic arthritis than in the general population.7... 

Hammond, BR, Fuld, K, and Currancelentano, J, 1995. Macular pigment density in monozygotic twins. Invest Ophthalmol Vis Sci 36, 2531-2541. 

The concordance rate of mood disorders is 60-80% for monozygotic twins and 14-20% for dizygotic twins. Linkage studies suggest that certain loci on genes and the X chromosome may contribute to genetic susceptibility of bipolar disorder,... 

Figure 1. Path diagrams for (a) parallel form reliability, (b) monozygotic twins reared apart, (c) unrelated individuals reared together, and (d) monozygotic twins reared together.

The correlation is not squared. Figure lb illustrates the correlation for a trait, represented by the boxes, between monozygotic twins reared apart (MZAs). 

Figure Id shows the correlation between monozygotic twins reared together. We have simply added a latent variable to represent common or shared environmental influence (C). This model represents the obvious fact that monozygotic twins reared together (MZTs) can be similar for both genetic and environmental reasons and that the correlation is confounded. Thus the equation ...

Table 5. Intraclass correlations, confidence intervals, samples sizes, and test utilized for IQ in five studies of monozygotic twins reared apart...

Contrary to Staples claim, the evidence for genetic influence on IQ has become much stronger in recent years and a number of important discoveries have been made. I summarize the key findings in a few tables and figures. Table 5 shows the most direct evidence regarding the heritability of IQ, the correlations for monozygotic twins reared apart.2... 

Juel-Nielsen, N. (1980). Individual and Environment Monozygotic twins reared apart (revised edition of 1965 monograph). New York International Universities Press. 

Moloney, D. P., Bouchard, T. J., Jr., Segal, N. L. (1991). A genetic and environmental analysis of the vocational interests of monozygotic and dizygotic twins reared apart. Journal of Vocational Behavior, 39, 76-109. 

Shields, J. (1962). Monozygotic twins Brought up apart and brought up together. London Oxford University Press. 

Concordance rates are compared in monozygotic (identical) and dizygotic (fraternal) twins to assess the contribution of genes to a trait These rates can be used to estimate heritability, the proportion of variation in a trait caused by genes. 

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